Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/70—Carbohydrates; Sugars; Derivatives thereof
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/70—Carbohydrates; Sugars; Derivatives thereof
  • A61K31/7042—Compounds having saccharide radicals and heterocyclic rings
  • A61K31/7052—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides
  • A61K31/706—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom
  • A61K31/7064—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom containing condensed or non-condensed pyrimidines
  • A61K31/7076—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom containing condensed or non-condensed pyrimidines containing purines, e.g. adenosine, adenylic acid
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P3/00—Drugs for disorders of the metabolism
  • A61P3/08—Drugs for disorders of the metabolism for glucose homeostasis
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P43/00—Drugs for specific purposes, not provided for in groups A61P1/00-A61P41/00
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
  • C07H19/00—Compounds containing a hetero ring sharing one ring hetero atom with a saccharide radical; Nucleosides; Mononucleotides; Anhydro-derivatives thereof
  • C07H19/02—Compounds containing a hetero ring sharing one ring hetero atom with a saccharide radical; Nucleosides; Mononucleotides; Anhydro-derivatives thereof sharing nitrogen
  • C07H19/04—Heterocyclic radicals containing only nitrogen atoms as ring hetero atom
  • C07H19/052—Imidazole radicals

Definitions

• This invention generally relates to ,-purine nucleosides, especially to 1- ⁇ -D-ribofuranosyl-5-aminoimidazole-4-carboxamide ("5-amino-4-imidazolecarboxamide riboside” or "AICA riboside”) prodrugs. It also relates to the preparation, use and administration of these compounds which, when introduced into the body, will metabolize into their active forms. This invention also relates to ischemic syndrome treatments, anticonvulsant therapeutic agents, methods and treatment of seizure and related disorders, and to lowering blood glucose and the treatment of blood glucose-related disorders including diabetes mellitus. Background of the Invention
• the present invention is directed to compounds which act as prodrugs of AICA riboside and certain analogs of it.
• AICA riboside monophosphate is a naturally occurring intermediate in purine biosynthesis.
• AICA riboside is also naturally occurring and is now known to enable adenosine release from cells during net ATP catabolism. By virtue of its adenosine releasing abilities, AICA riboside has many therapeutic uses. However, we have discovered that AICA riboside does not cross the blood-brain barrier well and is inefficiently absorbed from the gastrointes tinal tract; both characteristics decrease its full potential for use as a therapeutic agent.
• AICA riboside, and AICA riboside pro-drugs and analogs can be used to lower blood glucose levels in animals, including rats, rabbits, dogs and man. These compounds are surprisingly efficacious for lowering blood sugar and are believed to be partially causing their effect by decreasing hepatic gluconeogenesis. These compounds will be useful for the treatment of animals for conditions including hyperglycemia, insulin resistance, insulin deficiency, diabetes mellitis, Syndrome X, to control the hyperglycemia and/or hyperlipidemia associated with total parenteral nutrition, or a combination of these effects.
• AICA riboside does not have the enhanced bioavailability as described for those pro-drugs set forth herein as useful for penetrating the gut barrier, it may be nevertheless useful for the above conditions because AICA riboside itself will be present in amounts sufficient to reach the liver, as we have also discovered.
• AICA riboside monophosphate is implicated by our studies to be the causative agent and, accordingly, it and monophosphate forms of prodrug and analog compounds noted herein are within the scope of our invention.
• Adenosine, 9- ⁇ -D-ribofuranosyladenine belongs to the class of biochemicals termed purine nucleosides and is a key biochemical cell regulatory molecule, as described by Fox and Kelly in the Annual Reviews of Biochemistry, Vol. 47, p. 635, 1978.
• Adenosine interacts with a wide variety of cell types and is responsible for a myriad of biological effects.
• Adenosine serves a major role in brain as an inhibitory neuromodulator (see Snyder, S.H., Ann. Rev. Neural Sci. 8:103-124 1985, Marangos, et al., NeuroSci and Biobehav. Rev. 9; 421-430 (1985), Dunwiddie, Int. Rev. Neurobiol., 27:63-130 (1985)). This action is mediated by ectocellular receptors (Londos et al., Regulatory Functions of Adenosine. pp. 17-32 (Berne et al., ed.) (1983)).
• adenosine and its metabolically stable analogs have profound anticonvulsant and sedative effects (Dunwiddie et al., J. Pharmacol, and Exptl. Therapeut.. 220:70-76 (1982); Radulovacki et al., J. Pharmacol. Exptl. Thera., 228:268-274 (1981)) that are effectively reversed by specific adenosine receptor antagonists.
• adenosine has been proposed to serve as a natural anticonvulsant, and agents that alter its extracellular levels are modulators of seizure activity (Dragunow et al., Epilepsia 26:480-487 (1985); Lee et al., Brain Res.. 21:1650-164 (1984)).
• adenosine is a potent vasodilator, an inhibitor of immune cell function, an inhibitor of granulocyte oxygen free radical production, an anti-arrhythmic, and an inhibitory neuromodulator. Given its broad spectrum of biological activity, considerable effort has been aimed at establishing practical therapeutic uses for adenosine and its analogs.
• adenosine Since adenosine is thought to act at the level of the cell plasma membrane by binding to receptors anchored in the membrane, past work has included attempts to increase extracellular levels of adenosine by administering it into the blood stream. Unfortunately, because adenosine is toxic at concentrations that have to be administered to a patient to maintain an efficacious extracellular thera-peutic level, the administration of adenosine alone is of limited therapeutic use. Further, adenosine receptors are subject to negative feedback control following exposure to adenosine, including down-regulation of the receptors.
• Extracellular levels of adenosine can be increased by the use of chemicals that inhibit enzymatic degradation of adenosine.
• Previous work has focused on identifying inhibitors of adenosine deaminase, which participates in the conversion of adenosine to inosine.
• Adenosine deaminase activity is inhibited by coformycin, 2'-deoxycoformycin, and erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride.
• adenosine receptor agonists and antagonists have been generated having structural modifications in the purine ring, alterations in substituent groups attached to the purine ring, and modifications or alterations in the carbohydrate moiety.
• Halogenated adenosine derivatives appear to have been promising as agonists or antagonists and, as described by Wolff et al. in the Journal of Biological Chemistry. Vol. 252, p. 681, 1977, exert biological effects in experimental systems similar to those caused by adenosine.
• Derivatives with N-6 or 5'- substitutions have also shown promise.
• adenosine deaminase inhibitors prevent the degradation of deoxyadenosine which is a potent immunotoxin. (Gruber et al., Ann. New York Acad. Sci. 451:315-318 (1985)).
• Such compounds would also be useful in the prophylactic or affirmative treatment of pathologic states involving increased cellular excitation, such as (1) seizures or epilepsy, (2) arrhythmias (3) inflammation due to, for example, arthritis, autoimmune disease.
• ARDS Adult Respiratory Distress Syndrome
• ARDS Adult Respiratory Distress Syndrome
• membtanes as occurs during dialysis or with heart-lung machines.
• the compounds useful in the invention may be used to accomplish these ends.
• adenosine Compounds which selectively increase extracellular adenosine will also be used in the prophylactic protection of cells in the hippocampus implicated in memory.
• the hippocampus has more adenosine and glutamate receptors than any other area of the brain. Accordingly, as described below, it is most sensitive to stroke or any condition of low blood flow to the brain.
• Some recent studies support the theory that Alzheimer's disease may result from chronic subclinical cerebral ischemia.
• the compounds of the invention will be used for the treatment and/or prevention of both overt stroke and Alzheimer's disease.
• Adenosine has been shown to be a potent inhibitor of glutamate release in brain.
• the CA-1 region of brain is selectively sensitive to post-stroke destruction.
• studies where observations were made at one, three and six days post-stroke the CA-1 area was shown to be progressively destroyed over time.
• cyclohexyladenosine (“CHA"), a global adenosine agonist, was given shortly after the stroke, the CA-1 area was markedly protected.
• CHA cyclohexyladenosine
• That beneficial effect was also seen in the survival rate of the animals. Because of its global effect, however, CHA has non-specific side effects. For example it undesirably will lower blood pressure and could remove blood from the ischemic area, thereby causing further decreased blood flow.
• the compounds of the invention described and claimed herein not only show the beneficial adenosine release (glutamate inhibiting properties) but are both site and event specific, avoiding the unwanted global action of known adenosine agonists. These compounds will also be used in the treatment of neurodegenerative diseases related to the exaggerated action of excitatory amino acids, such as Parkinson's disease.
• AICA riboside prodrugs of this invention may be used for such purposes as well.
• mast cell activation can be down-regulated by immunotherapy (allergy shots) or by mast cell stabilizers such as cromalyn sodium, corticosteroids and aminophylline.
• mast cell stabilizers such as cromalyn sodium, corticosteroids and aminophylline.
• agents which interfere with the products of mast cells such as anti-histamines and adrenergic agents.
• the mechanism of action of mast cell stabilization is not clearly understood.
• aminophylline it is possible that it acts as an adenosine receptor antagonist.
• agents such as cromalyn sodium and the corticosteroids are not as well understood.
• AICA riboside and prodrugs of AICA riboside as antiviral agents and for increasing the antiviral activity of AZT is disclosed in commonly-assigned U.S. Patent Application Serial No. 301,454, "Antivirals and Methods for Increasing the Antiviral Activity of AZT", filed January 24, 1989, the disclosure of which is incorporated herein by reference.
• AICA riboside Certain derivatives of AICA riboside have been prepared and used as intermediates in the synthesis of nucleosides such as adenosine or nucleoside analogs such as 3'-deoxy-thio-AICA riboside. See, e.g., U.S. Patent No. 3,450,693 to Suzuki et al.; Miyoshi et al., Chem. Pharm. Bull. 24.(9): 2089-2093 (1976); Chambers et al., Nucleosides & Nucleotides 2(3) : 339-346 (1988); Srivastava, J. Org. Chem. 40(20) : 2920-2924 (1975).
• Hyperglycemia has been reported to be associatectwith a poor prognosis for stroke. (Helgason, Stroke 19(8): 1049-1053 (1988). In addition, mild hypoglycemia induced by insulin treatment has been shown to improve survival and morbidity from experimentally induced infarct. (Le May et al., Stroke 19(11) : 1411-1419 (1988)).
• AICA riboside and the prodrugs of the present Invention will be useful to help protect against ischemic injury to the central nervous system (CNS) at least partly by their ability to lower blood glucose.
• Hyperglycemia and related diabetic conditions are generally divided into “type I” or severe (typically insulin requiring) and “type II” or mild (typically controlled by oral hypoglycemic agents and/or diet and exercise).
• Type I diabetic patients have severe insulin deficiency with complications typically including hyperglycemia and ketoacidosis.
• Type II diabetic patients typically have milder insulin deficiency or decreased insulin sensitivity associated with hyperglycemia predominantly from acceler- ated hepatic gluconeogenesis. Both forms of diabetic conditions are associated with atherosclerosis and ischemic organ injury.
• Oral hypoglycemic agents that are currently available clinically include sulfonylureas (e.g., tolbutamide, tolazamide, acetohexamide, chlorpropamide, glyburide, glipizide) and biguanides (e.g. phenformin and metformin)-.
• sulfonylureas e.g., tolbutamide, tolazamide, acetohexamide, chlorpropamide, glyburide, glipizide
• biguanides e.g. phenformin and metformin
• the sulfonylurea class of drugs are not ideal hypoglycemic agents for a variety of reasons; moreover, they have been associated with increased risk of cardiovascular disease and can be of insufficient efficacy for many Type II diabetes patients.
• the biguanide class of drugs reduce blood sugar by increasing peripheral utilization of glucose and by decreasing hepatic glucose production, both effects presumably caused by inhibiting oxidative phosphorylation.
• the biguanides have been associated with fatal lactic acidosis and, for that reason, are at present not available clinically in the United States.
• Fructose diphosphatase has been suggested as an ideal target for new hypoglycemic agents, since it is one of two control steps in gluconeogenesis. (See, Sherratt, supra 1981) However, therapeutic agents which lower its activ- ity are not presently clinically available. Fructose diphosphatase is inhibited by AMP and activated by ATP, being responsive to the cellular energy charge. Pyruvate carboxylase, the other major regulatory step in gluconeogenesis, is the first committed step towards glucose production and is regulated by the availability of acetyl CoA; however, its inhibition would result in interruption of mitochondrial function.
• the present invention is directed to purine prodrugs and analogs which exhibit and, in some cases improve upon, the positive biological effects of AICA riboside and other adenosine releasing compounds without the negative effects of systemic adenosine.
• the compounds herein defined may be used as prodrugs.
• the novel compounds typically exhibit one or more of the following improvements over
• AICA riboside 1) more potent adenosine releasing effects; 2) increased half-lives; 3) increased brain penetration; 4) increased oral bioavailability; 5) increased myocardial targeting; 6) in some cases efficacy improvements over AICA riboside itself.
• the AICA riboside prodrugs of this invention may be used in treatment and prevention of a number of disorders, some of which already have been mentioned.
• the present invention is directed to prodrugs of AICA riboside.
• AICA riboside has very limited oral bioavailability. Accordingly, we have found that when AICA riboside is given orally, very little or none of it reaches the tissue(s) which comprise its site(s) of action.
• the present invention is based on our finding that oral administration of prodrugs of AICA riboside result in enhanced levels of AICA riboside in the blood and other tissues, as compared with oral administration of AICA riboside itself.
• Use of prodrugs of AICA riboside allow for delivery of therapeutically effective amounts of AICA riboside to the tissue (s) to be treated.
• AICA riboside has less than full gastrointestinal tract penetration and relatively low blood brain-barrier penetration.
• Derivatization of adenosine releasing agents, including AICA riboside has been undertaken with the goals of increasing penetration of AICA riboside into the brain and through the gut by delivering it as a brain and/or gut permeable form that avoids first pass metabo lism and, while reaching the target regenerates into the parent compound (a prodrug strategy).
• the present invention is directed to compounds which act as prodrugs of AICA riboside and their use as prodrugs in therapies as described below.
• These prodrug compounds comprise a modified AICA riboside having an AICA ribosyl moiety and at least one hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety per equivalent weight of AICA ribosyl moiety.
• AICA riboside may be chemically modified to yield an AICA riboside prodrug wherein one or more of the hydroxyl oxygens of the ribosyl moiety (i.e. 2'-, 3'- or 5'-) is substituted with a hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety.
• the prodrug compounds of the present invention are useful in treating a variety of clinical conditions where increasing extracellular levels of adenosine would be beneficial. Accordingly, the present invention is directed to the prophylactic and affirmative treatment of such conditions as stroke, Alzheimer's disease, homocys- teineuria, skin flap and reconstructive surgery, post- ischemic syndrome and other seizure-related conditions, spinal cord ischemia, intraoperative ischemia especially during heart/lung bypass procedures, cardioplegia, diabetes mellitus, hyperglycemic conditions including that associated with total parenteral nutrition, and myocardial ischemia, including angina and infarct, using these prodrug compounds.
• prodrugs are useful in treating other indications where AICA riboside has exhibited activity and where oral administration is preferred or would be advantageous. Thus, they are useful in delivering AICA riboside in an orally bioavailable form.
• This invention is also directed to pharmaceutical compositions comprising an effective amount of a prodrug compound of the present invention in a pharmaceutically acceptable carrier.
• Preferred prodrug compounds include those where at least one of the hydroxyl oxygens of the ribosyl moiety is substituted with a hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety.
• One preferred class of compounds' are those wherein at least one hydroxyl oxygen is substituted with a hydrocarbyloxycarbonyl moiety.
• One preferred class of prodrug compounds comprises compounds wherein either of the 3'- or 5'- hydroxyl oxygens, or both, of the ribosyl moiety is substituted with a hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety.
• preferred prodrug compounds include those substituted with 1 to 3 short chain acyl ester groups.
• compounds having a 5'-pivaloyl or isobutyryl substitution or having a 2',3',5'- triacetyl substitution have shown enhanced bioavailability when given orally.
• compounds having a 5'-butyfyl or 3',5'-diacetyl substitutions are also showing enhanced oral bioavailability.
• Another preferred group of compounds include those having a 3'-hydrocarbyloxycarbonyl substitution, especially those having an isobutoxycarbonyl or neopentoxycarbonyl substitution.
• the present invention is directed to a class of novel prodrug compounds.
• these compounds comprise a modified AICA riboside having an AICA ribosyl moiety and at least one hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety, or combinations thereof, per equivalent weight of AICA ribosyl moiety, provided that said prodrug does not have three acetyl, propionyl or benzoyl moieties per equivalent weight of AICA ribosyl moiety and that it is not dibenzoyl-substituted or monoacetyl substituted at the 5'- position of the ribosyl moiety.
• a particularly preferred group of compounds includes those mono- or di- substituted with a short chain acyl ester group. Such compounds include those having a 5'- acyl ester substitution or a 3',5'-diacyl substitution.
• Preferred diacyl substituted compounds include the 3',5'- diacetyl substituted compound and the 5'-n-butyryl substituted compound.
• Especially preferred compounds include those having either a 5'-pivalyl or 5'-isobutyryl substitution.
• Another aspect of the present invention provides prodrugs of carbocyclic AICA riboside.
• alkyl refers to saturated aliphatic groups, including straight, branched and carbocyclic groups.
• alkynyl refers to unsaturated groups having at least one triple bond [e.g. CH 3 C ⁇ C(CH 2 ) 2 -] and includes both straight chain and branched-chain groups.
• aryl refers to aromatic hydrocarbyl and heteroaromatic groups which have at least one aromatic ring.
• alkylene refers to straight and branched-chain alkylene groups which are biradicals, and includes, for example, groups such as ethylene, propylene, 2-methyl- propylene (e.g. 3-methylpentylene and
• hydrocarbyl denotes an organic radical composed of carbon and hydrogen which may be aliphatic (including alkyl, alkenyl, and alkynyl groups and groups which have a mixture of saturated and unsaturated bonds), alicyclic (carbocyclic), aryl (aromatic) or combinations thereof; and may refer to straight-chained, branched- chain, or cyclic structures or to radicals having a combination thereof, as well as to radicals substituted with halogen atom(s) or heteroatoms, such as nitrogen, oxygen, and sulfur and their functional groups (such as amino, alkoxy, aryloxy, carboxyl, ester, amide, carbamate or lactone groups, and the like), which are commonly found in organic compounds and radicals.
• hydrocarbyloxycarbonyl refers to the group wherein R' is a hydrocarbyl group.
• hydrocarbylcarbonyl refers to the group wherein R' is a hydrocarbyl group.
• esters refers to a group having a linkage, and includes both acyl ester groups and carbonate ester groups.
• halo or halogen refers to fluorine, chlorine, bromine and iodine.
• carbonate ester refers to the group wherein R' is hydrocarbyl or to compounds having at least one such group.
• acyl ester refers to the group wherein R' is hydrocarbyl or to compounds having at least one such group.
• mixed ester refers to compounds having at least one carbonate ester group and at least one acyl ester group or to compounds having combinations of different acyl ester or carbonate ester groups.
• carbocyclic AICA riboside refers to an analog of AICA riboside wherein the oxygen atom of the ribosyl ring has been replaced by a carbon atom. Accordingly, carbocyclic AICA riboside has the following structure and the following conventional number system for the rings, as noted, is used:
• prodrug refers to compounds which are derivatives of a parent compound (such as AICA riboside) which have been derivativized to assist the parent compound in getting to the desired locus of action. The derivitized portion of the prodrug is cleaved (metabol- ized) or activated to give the parent compound either in transit or at the desired locus. Typically a prodrug may allow the parent compound to cross or better cross a biological barrier such as the gut epithelium or the blood-brain barrier, at which point it is cleaved to giva the parent compound.
• oral bioavailability refers to the quantity of drug reaching the bloodstream after oral administration. Accordingly, an “orally bioavailable” drug is one which is well absorbed from the gut and reaches the blood stream when administered orally.
• FIG. 1 depicts the activities of AICA riboside and Prodrug A in preventing homocysteine thiolactone-induced seizures in mice.
• FIG. 2 depicts the activities of AICA riboside and Prodrug A in inducing adenosine production in ischemic rat heart tissue.
• FIG. 3 depicts the effects of oral administration of AICA riboside and Prodrug A on ZMP concentration in rat heart tissue.
• FIG. 4 depicts the effect of Prodrug A and AICA riboside on adenosine release in cell culture.
• FIGS. 5A and 5B depict the effects of oral administration of AICA riboside and Prodrug A on ZMP concentration in rat liver.
• FIG. 6 depicts the activities of equimolar doses of ribose and AICA riboside in lowering blood glucose in fasted mice.
• FIG. 7 depicts the effect of AICA riboside on plasma glucose in fasted and non-fasted rats.
• FIG. 8 depicts the effect of AICA riboside on serum glucose in humans.
• FIG. 9 depicts the effects of AICA riboside on liver glycogen.
• FIGS. 10A to 10D depict the effects of AICA riboside on serum lactate and pyruvate in rats.
• FIGS. 11A and 11B depict the effect of AICA riboside on blood glucose levels in conjunction with liver ZMP levels.
• FIG. 12 depicts the activities of AICA riboside, ZMP and AMP in inhibiting fructose 1,6-diphosphatase in rabbit liver.
• FIGS. 13A and 13B depict insulin levels in human plasma after administration of a 50 mg/kg dose of AICA riboside.
• FIG. 14 depicts hypoglycemic effects of equimolar oral doses of some of the prodrugs of the present invention.
• FIG. 15 depicts the effects of inhibition of adeno- sine kinase on the PTZ induced seizures.
• FIG. 16 depicts the effect of ZMP and carbocyclic ZMP as inhibitors of fructose 1,6-diphosphatase.
• FIG. 17 depicts the effect of chronic AICA riboside administration on triglyceride levels in diabetic rats.
• FIG. 18 depicts plasma concentrations of AICA riboside in dogs after oral administration.
• FIGs. 19A and 19B depict adenosine and AMP levels of AICA riboside and certain 3'-carbonate esters of AICA riboside in ischemic rat heart.
• FIG. 20 depicts plasma concentration of AICA riboside in dog-following oral administration of a prodrug of AICA riboside (3,5-diacetyl AICA riboside).
• FIG. 21 depicts the effect of AICA riboside on serum glucose levels in streptozotocin-induced diabetic mice.
• FIG. 22 depicts the effect of chronic AICA riboside treatment in streptozotocin-induced diabetic rats.
• FIG. 23 depicts the effect of chronic AICA riboside treatment on water consumption by streptozotocin-induced diabetic rats.
• FIG. 24 depicts the effects of chronic AICA riboside treatment on hepatic fructose 1,6-diphosphatase activity in streptozotocin-induced diabetic rats.
• FIG. 25 depicts the effect of AICA riboside on hepatic fructose 1,6-diphosphate levels in mice.
• FIG. 26 depicts a comparison of the effects, of the hypoglycemic agent glyburide and AICA riboside in fasted and non-fasted mice.
• FIG. 27 depicts the effect of AICA riboside on serum glucose levels in streptozotocin-induced diabetic rats.
• Preferred prodrug compounds of the present invention comprise a modified AICA riboside having an AICA ribosyl moiety and at least one hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety per equivalent weight of AICA ribosyl moiety.
• AICA riboside prodrugs of the formula:
• X 1 , X 2 and X 3 are independently (a) hydrogen, (b) wherein R
• R 1 is independently hydrocarbyl or independently mono- or dihydrocarbylamino and R 2 is independently hydrocarbyl, or (c) two of X 1 , X 2 and X 3 taken together form a cyclic carbonate ring, provided that at least one of X 1 , X 2 and X 3 is not hydrogen.
• prodrugs where one or more of X 1 , X 2 and X 3 comprises a short chain hydrocarbylcarbonyl group are preferred.
• prodrugs where X 1 is isobutyryl or pivaloyl and X 2 and X 3 are both hydrogen (compounds 10 and 11 of Table I) and where X 1 , X 2 and X 3 are acetyl (compound Cl of Table I).
• prodrugs where X 1 is n-butyryl and X 2 and X 3 are both hydrogen, and where X 1 and X 3 are both acetyl and X 2 is hydrogen.
• certain prodrug compounds which have been isolated in an advantageous crystalline form, in particular 2',3',5'-triacetyl AICA riboside (Compound C1 of Table I) , 3',5'-diacetyl AICA riboside (Compound 22 of Table I) and 3'-neopentoxycarbonyl (Compound 17 of Table I).
• the leaving groups comprise acetate which is advantageously relatively pharmacologically silent.
• the preferred novel prodrug compounds of the present invention include those having the following formula: (I)
• X 1 , X 2 , and X 3 are independently (a) hydrogen, or (b) wherein R 1 is independently hydrocarbyl preferably of from 1 to about 24 carbon atoms or mono- or di-hydrocarbylamino, R 2 is independently hydrocarbyl preferably of form 1 to about 24 carbon atoms or (c) two of X 1 , X 2 and X 3 taken together form a cyclic carbonate group; with the proviso that not all of X 1 , X 2 and X 3 are hydrogen, acetyl, propionyl or benzoyl, or if one bf X 11 X 2 and X 3 is hydrogen, the other two are not both benzoyl, or if X 2 and X 3 are hydrogen, then X, is not acetyl.
• Preferred R 1 and R 2 groups include lower alkyl groups.
• One preferred class of lower alkyl groups are those having at least one secondary or tertiary carbon atom.
• Another preferred class of lower alkyl groups are those having up to about 6 carbon atoms and optionally having a secondary or tertiary carbon atom.
• Hydrocarbyl groups having more than 24 carbon atoms may be used and are considered to be within the scope of the present invention.
• Preferred compounds include those having one or two ester groups. Especially preferred are compounds having an ester group at either the 3'- or 5' - position of both positions of the ribosyl ring.
• One preferred class of compounds comprises carbonate esters. Particularly preferred carbonate esters include compounds wherein X 1 or X 3 is especially preferred
• X 2 is hydrogen.
• One such preferred group of compounds are those having a 3'-carbonate ester group.
• Especially preferred carbonate ester compounds include those where X 1 and X 2 are both hydrogen and X 3 is isobutoxycarbonyl (compound No. 1 of Table I) or ne ⁇ pentoxycarbonyl (Compound No. 17 of Table I).
• Other preferred 3'- substituted carbonate esters include compounds Nos. 4, 3, and 7 of Table I.
• prodrug compounds include compounds which have, enhanced water solubility. Such compounds are believed to exhibit enhanced bioavailability when given orally due to improved absorption from the gastrointestinal tract. For this reason, it is believed that prodrug compounds having one or two acyl ester groups are particularly advantageous. Especially preferred are short chain ester groups having less than about 6 carbon atoms. In particular, we have found compounds having an acyl ester at the 5' position or both the 3 » and 5* positions of the ribosyl ring to be preferred. In particular, we have found compounds No. 10 (where X 1 is isobutyryl and X 2 and X 3 are both hydrogen), and No.
• Reaction (1) is carried out by combining II, AICA riboside, and III, the appropriate acid chloride, acid anhydride or chloroformate, in solvents.
• the acid chloride may be conveniently prepared by conventional procedures such as reaction of the corresponding acid with thionyl chloride. Some acid chlorides and acid anhydrides are commercially available. Many chloroformates are commercially available; also, the chloroformates may be conveniently prepared by conventional procedures known to those skilled in the art by the reaction of phosgene with the appropriate alcohol.
• Reaction (1) is conducted at a temperature of from about -10oC to about 5oC, preferably from about -5oC to about 0oC and is generally complete within about 2 to about 4 hours. For ease of handling. the reaction is carried out in solvents.
• Suitable solvents include dimethylformamide (DMF), pyridine, methylene chloride and the like.
• DMF dimethylformamide
• pyridine pyridine
• methylene chloride methylene chloride
• the reaction is carried out at ambient pressure.
• the reaction product(s) are isolated by conventional procedures such as column chromatography, crystallization and the like.
• the reaction may result in a mixture of products, mono, di, and tri-esters at the 2'-, 3'- and/or 5'- positions of the ribosyl moiety.
• the product esters may be separated by conventional procedures such as thin layer chromatography (TLC) , high pressure liquid chromatography (HPLC), column chromatography, crystallization, and the like which are well known to those skilled in the art.
• the 5'-monoesters may be conveniently prepared according to the following reaction scheme to give an intermediate blocked at the 2' and 3' positions:
• X 1a is and DbAg is a deblocking agent.
• Reaction (2) is conducted by combining II, IV, V and
• Reaction (3) is the reaction of intermediate VII with the appropriate acid chloride, acid anhydride or chloroformate and is carried out as described in connection with Reaction (1).
• Reaction (4) is an optional step to remove, if desired, the cyclic blocking group from the 2' and 3' positions. It is carried out by reacting with IX, the appropriate deblocking agent. Suitable deblocking agents include H + resin in water/ acetone, tetraethyl-amm ⁇ nium fluoride/THF, acetic acid/water, formic acid/water and the like. Such deblocking reactions are conventional and well known to those skilled in the art.
• Mixed ester compounds may be conveniently prepared by first reacting AICA riboside with the appropriate acid chloride or acid anhydride according to Reaction (1) to add the acyl ester group and then reacting the acyl ester- substituted compound with the appropriate chloroformate according to Reaction (1) to obtain the mixed ester.
• mixed ester compounds may be prepared by first converting AICA riboside to a monoacyl ester according to Reaction (1) or Reaction (2) and then reacting the purified monoacylated product with the appropriate chloroformate according to Reaction (1) .
• some mixed esters are prepared by first converting AICA riboside to a mono-alkoxycarbonate according to Reaction (1) or (2) and then reacting the purified carbonate ester with an appropriate acid chloride or acid anhydride according to Reaction (1).
• Carbocyclic AICA Riboside Compounds are prepared by first converting AICA riboside to a mono-alkoxycarbonate according to Reaction (1) or (2) and then reacting the purified carbonate ester with an appropriate acid chloride or acid anhydride according to Reaction (1).
• carbocyclic AICA riboside has adenosine releasing agent properties.
• the present invention also provides a novel class of prodrugs of carbocyclic AICA riboside, and the use of carbocyclic AICA riboside and its prodrugs as adenosine releasing agents. These prodrugs are also useful as antiviral agents.
• prodrug compounds comprise a modified carbocyclic AICA riboside having a carbocyclic AICA ribosyl moiety which comprises an AICA moiety and a cyclopentyl moiety (where a carbon has replaced the oxygen in the ribosyl ring), and at least one hydrocarbyloxycarbonyl or hydrocarbylcarbonyl moiety per equivalent weight of carbocyclic AICA ribosyl moiety.
• the carbocyclic AICA riboside and its prodrug compounds are useful in treating a variety of clinical conditions where increasing extracellular levels and release of adenosine would be beneficial.
• This invention is also directed to pharmaceutical compositions comprising an effective amount of carbocyclic AICA riboside or a prodrug compound thereof in a pharmaceutically acceptable carrier.
• carbocyclic AICA riboside prodrugs may be conveniently prepared by methods similar to those used in the preparation of the AICA riboside prodrugs described herein, substituting carbocyclic AICA riboside for AICA riboside as a starting material.
• the prodrug compounds of the present invention are useful in treating a variety of clinical conditions where increased extracellular levels (and/or release) of adenosine are beneficial.
• these compounds are useful in stroke therapy, either by prophylactic treatment or by treatment soon after the cerebral vascular event. These compounds are useful in mitigating the effects of other post- ischemic syndromes in the central nervous system, including the brain and spinal chord.
• EAA's appear to be the major factor involved in post-stroke cell damage, blockade of EAA release in brain with adenosine might be beneficial in stroke therapy.
• Known glutamate receptor blockers have however been shown to lack specificity and produce many undesirable side effects, and the undesirable effects of adenosine administration have been noted.
• low doses of adenosine or an adenosine agonist with a high A 1 to A 2 affinity ratio or co-administration of a centrally acting agonist with an antagonist that cannot enter the central nervous system might avoid cardiovascular side effects and bind the A. receptors in the hippocampal regions thereby preventing or reducing EAA release.
• AICA-riboside has been shown to protect against cellular degeneration that results after experimentally induced brain ischemia in two different animal model systems.
• the claimed prodrugs, by delivering AICA riboside should provide similar efficacy.
• AICA-riboside prevented the degeneration of hippocampal CA-1 cells, which in the control animals (non AICA-riboside treated) were virtually completely destroyed.
• Both intracerebroventricular (ICV) and IP administration of AICA riboside was effective in the gerbil model.
• two different rat models of focal ischemia were also used to evaluate AICA-riboside.
• One model employed partial reperfusion and the second total reperfusion. Both protocols showed a highly significant reduction in infarct size when a 800 mg/kg dose of AICA-riboside was given IP.
• These compounds are also useful in treating other ischemic conditions, particularly those involving myocardial ischemia such as heart attacks and angina pectoris.
• adenosine is normally released and assists in maintaining the patency of ischemic vessels through vasodilation and inhibition of granulocyte free radical production and concomitant microvascular plugging, as described below.
• the prodrug compounds of the present invention enhance adenosine release and, therefore enhance the normal protective effect of adenosine during such an ischemic event.
• Adenosine levels are not altered significantly throughout the patient because alterations of adenosine production only occur in areas of, and at the time of, net ATP use and because adenosine is rapidly degraded. Thus, there will be a localized increased level of extracellular adenosine instead of a systemic or generalized adenosine enhancement.
• the prodrugs of the present invention should be present at the earliest possible moment. Accordingly, prophylactic use of these prodrugs may slow or interrupt the damaging process early enough to prevent any permanent damage. For example, the increased micro- vascular blood flow from vasodilation and decreased white cell sticking could maintain microvascular patency as well as in a sense wash away clots, clot promoting matter, or other deleterious agents from the proximal atherosclerotic regions.
• prodrugs of the present invention when taken prophylactically would enhance adenosine release during an ischemic event, a heart attack patient undergoing such treatment would have a greater chance of not dying of a sudden arrhythmia before entry to the hospital.
• a prophylactic therapeutic regimen would protect the microvascular system and allow a longer time frame in which to institute thrombolytic therapy.
• prodrugs of the present invention will also be useful in combination with thrombolytic agents such tissue plasminogen activator, streptokinase, and the like and also with other agents which are either free radical scavengers or agents which prevent the production of free radicals.
• the prodrugs of the present invention are useful in treating reduced blood flow caused by myocardial arrhythmia.
• Prophylactic treatment with AICA riboside has been shown to result in decreased numbers of premature ventricular depolarizations and ventricular tachycardia episodes in animals and, more recently, decreased fatal ventricular fibrillation.
• the prodrugs of the present invention may be useful in treating other conditions in which administration of AICA riboside has been beneficial.
• these include conditions such as treatment of autoimmune and inflammatory diseases and neurodegenerative diseases, conditions potentially associated with chronically low adenosine (including autism, insomnia, cerebral palsy, schizophrenia and other neuropsychiatric conditions), conditions associated with hyperglycemia (including diabetes mellitus and/or resulting from total pare ⁇ teral nutrition), allergic conditions (especially by preventing the release of pharmacologically active substances by mast cells), and viral conditions, especially those associated with the human immunodeficiency disease.
• AICA riboside is inef- ficiently absorbed from the gut and is poor in crossing the blood-brain barrier to penetrate the affected foci in the brain.
• the advantageous features of more efficient absorption from the GI tract and better crossing of the blood brain barrier of the prodrug compounds of the present invention should give them increased efficacity and improved therapeutic effect as compared to AICA-riboside itself.
• prodrug compounds of the present invention are useful as anticonvulsants and in preventing seizures in individuals with epilepsy including patients with homocysteineuria.
• AICA riboside and some of these prodrug compounds have been shown to be active in preventing homocysteine-induced seizures in laboratory animals.
• AICA riboside and the prodrugs of the present invention should be efficacious in reducing ischemic injury to the CNS.
• the enhanced localized adenosine should cause local vasodilation, decreased granulocyte activation and trapping, and decreased glutamate release and excitatory neurotoxicity.
• the mild hypoglycemia resulting from administration of these compounds is also protective.
• AICA riboside can cause hypoglycemia in rats, rabbits, dogs and man. This hypoglycemic effect may contribute to the anti-ischemic properties of the molecule. Ribose is known to lower blood glucose in several animal species, including man, in relatively high doses (on the order of about 1000 mg/kg) by an unknown mechanism, possibly by inhibition of phosphoglucomutase. Accordingly, in theory, AICA riboside could cause hypoglycemia at extremely high doses (approximately 3 gm/kg) due to its ability to deliver ribose phosphate to cells.
• ribose-1-phosphate which is converted ribose-5-phosphate
• ribose-5-phosphate may also lower blood sugar.
• AICA riboside to lower blood glucose in rabbits at doses an order of magnitude lower than those effective for ribose, as low as about 200 mg/kg (see Table VI) .
• hypoglycemic seizures and death were induced in rabbits and mice.
• rats We have found rats to also be sensitive to the hypoglycemic effects of AICA riboside.
• AICA riboside is potent in lowering blood glucose. (See e.g., Figure 6). In fasted mice AICA riboside may cause seizures at doses of 500 mg/Kg and above. In fasted mice (2 hours) a dose of 500 mg/Kg of AICA riboside reduced plasma glucose levels for 2-3 hours. In fasted mice (16 hours) a dose of 250 mg/Kg reduced glucose levels by 50% (p ⁇ .01) and 60% at doses of 500 and 750 mg/Kg (p ⁇ .01). Fasting therefore appears to potentiate the hypoglycemic effect of AICA riboside.
• AICA riboside as a hypoglycemic agent may be potentiated in a diabetic state.
• tolerance to the chronic administration of AICA riboside does not develop. Repeated administration of the drug for 6 days continues to yield a significant hypoglycemic response.
• AICA riboside induced hypoglycemia This leads to investigation of the mechanism of AICA riboside induced hypoglycemia. It appears that adenosine is not involved in the mechanisms of AICA riboside induced hypoglycemia, since adenosine and adenosine receptor agonists such as cyclohexyladenosine (CHA) and N-ethylcarboxamide adenosine (NECA) do not result in hypoglycemia but in fact produce a profound hyperglycemia (200-300% increases in plasma glucose, p ⁇ .01) when administered I.P. in either rats or mice.
• adenosine and adenosine receptor agonists such as cyclohexyladenosine (CHA) and N-ethylcarboxamide adenosine (NECA) do not result in hypoglycemia but in fact produce a profound hyperglycemia (200-300% increases in plasma glucose, p
• AICA riboside-induced hyperglycemia is reversed by adenosine receptor antagonists (theophylline and sulphophenyltheophylline). Additionally, the AICA riboside-induced hypoglycemia is not blocked by theophylline. It is therefore concluded that the AICA riboside effect on plasma glucose is not mediated by adenosine.
• high doses of AICA riboside suppress blood insulin levels even at early time points after administration of the dose.
• human subjects exhibit significant elevations of serum insulin levels with administration of AICA riboside which precede the drop in blood glucose levels. (See Figure 13) .
• a dose of 750 mg/Kg in mice was shown to increase liver glycogen by 55% (p ⁇ .0l) suggesting that the drug inhibits liver glycogenolysis or activates glycogen synthesis and, thereby, contributes to the lowered plasma glucose levels.
• Rats exhibit an elevation of liver glycogen and of serum lactate and pyruvate; however, the lactate to pyruvate ratio is not changed. The lactate elevation suggests an interruption in gluconeogenesis, while the lack of change in the lactate to pyruvate ratio suggests no effect on mitochondrial function.
• the glucose lowering effects of AICA riboside are related temporally to the generation and maintenance of liver ZMP levels in rats. (See Figures 11A and 11B). In studies employing rabbit liver, ZMP, but not AICA riboside, has been found to inhibit fructose diphosphatase ("FDPase”) with a K i of about 40 ⁇ M (see Figure 12).
• FDPase fructose diphosphatase
• Inhibition of pyruvate carboxylase, PEP carboxykinase or oxidative phosphorylation can interrupt mitochondrial function.
• AICA riboside does not interrupt mitochondrial function; the mild lactate build-up which occurs after administration of AICA riboside is not associated with a change in redox potential or a reduction in ATP pools. The mild lactate build up represents a minor interruption of the Cori cycle and should not, in itself, have detrimental effects. Doses of AICA riboside substantially higher than those causing elevation in lactate levels have been shown safe in toxicological studies.
• AICA riboside may be phosphorylated by adenosine kinase to give AICA riboside-5'-monophosphate ("ZMP").
• ZMP AICA riboside-5'-monophosphate
• fructose diphosphatase probably results from ZMP binding to the AMP inhibitory site of the enzyme.
• the enzyme falsely interprets a reduction in energy charge by the build-up in "false AMP", namely ZMP.
• ZMP can also cause an elevation of AMP levels (AMP is also an inhibitor of FDPase) via its inhibition of AMP deaminase.
• AMP is also an inhibitor of FDPase
• fructose diphosphatase may be inhibited using other ZMP analogs, including carbocyclic AICA riboside monophosphate.
• agents which cause or result in a build-up in ZMP include precursors in the de novo purine synthesis pathway or nucleosides, bases or prodrugs of such precursors. (See Lehninger, Biochemistry. p. 569 (1970)). Endogeneous ZMP levels may also be increased by agents which directly or indirectly inhibit AICA ribotide transformylase (thereby inhibiting folate metabolism), the enzyme which converts ZMP to 5'-formamido-imidazole-4-carboxamide ribonucleotide (precursor to inosinic acid).
• blood glucose levels may be decreased by administering agents which increase ZMP, either by increasing its synthesis or decreasing its conversion by AICA ribotide transformylase.
• Increased ZMP levels result in decreased FDPase activity and thus lower blood glucose levels.
• concomitant administration of one of these prodrugs of AICA riboside with an inhibitor of AICA ribotide transformylase may give enhanced hypoglycemic effects.
• Administration of any of the de novo purine synthesis intermediates (after the first committed step for purine synthesis, or their nucleosides or bases or their prodrugs, may similarly result in lowered blood glucose levels as mediated by ZMP.
• AMP deaminase inhibitors can also be used to raise AMP concentration and inhibit FDPase, and thereby treat hyperglycemic conditions such as diabetes mellitis.
• AICA riboside lowers blood glucose levels by at least three mechanisms.
• AICA riboside causes (1) an early elevation of serum insulin levels, probably due to increased pancreatic release of insulin.
• AICA riboside administration causes (2) increased glycogen storage related to increased synthesis and/or decreased breakdown of glycogen.
• the glycogen storage effects of AICA riboside are probably only partially contributory to its hypoglycemic effects, since surprisingly, in glycogen depleted states such as prolonged fasting, profound hypoglycemia is induced more readily, i.e. at lower AICA riboside doses.
• AICA riboside appears to lower blood glucose (3) by inhibiting gluconeogenesis at the level of fructose diphosphatase; an ideal mechanism of therapy for type II diabetic patients who exhibit a ⁇ celer- ated hepatic gluconeogluesis.
• Control of gluconeogenesis by inhibition of fructose diphosphatase is a preferred site of action in the gluconeogenesis pathway because fructose diphosphatase is specific for the synthesis of glucose; several other enzymes are used in both the synthesis and degradation pathways of glucose. Additionally, inhibition of fructose diphosphatase does not interfere with mitochondrial function.
• the combined effects from AICA riboside treatment namely, increased insulin release, direct inhibition of gluconeogenesis and decreased glycogen utilization provide a profound, yet safe, reduction in blood glucose levels.
• prodrugs of AICA riboside useful for increased delivery of the drug to the pancreas and liver after oral admihistration.
• AICA riboside itself is not well absorbed when given orally, administration of prodrugs of AICA riboside of the present invention, including acyl and carbonate esters, result in enhanced levels of serum AICA riboside and heart and liver ZMP.
• AICA riboside prodrugs of the present invention are useful in therapies for diabetes and related conditions.
• AICA riboside and these prodrugs are useful as a supplement to total parenteral nutrition as an agent to control hyperglycemia and/or hyperlipidemia.
• adenosine releasing agents such as AICA riboside prevent or reduce (ischemic) injury associated with atherosclerosis. Since ischemic injury to heart, brain, eyes, kidneys, skin and nerves constitute significant long term complications associated with both type I and type II diabetes, the anti-ischemic properties of AICA riboside, its prodrugs and related analogs, will thereby confer added therapeutic benefits to diabetic patients.
• AICA riboside lowers serum triglycerides in streptozotocin-induced diabetes in rats. (See Figure 17). Elevated triglycerides are associated with accelerated atherosclerosis and their normalization in those with diabetic conditions by the present invention should provide additional therapeutic utility in the treatment of diabetes.
• S-AICA ribosyl homocysteine is formed from AICA riboside and homocysteine utilizing the enzyme S-adenosyl homocysteine hydrolase. This compound is a prodrug of AICA riboside.
• AICA riboside is a weak inhibitor of adenosine kinase and that S-AICA riboside homocysteine is more potent. Inhibition of adenosine kinase by either AICA riboside or S-AICA ribosyl homocysteine can lead to increased adenosine release from cells undergoing net ATP catabolism.
• AMP 5'-nucleotidase is a highly regulated enzyme which has a regulatory protein which, when bound to the enzyme, inhibits its activity.
• AICA riboside or a metabo lite thereof may activate AMP 5'-nucleotidase by preventing the binding of the regulatory protein to the enzyme.
• AICA riboside has now been shown to be generated from ZMP during ischemia.
• the localized dephosphorylation of ZMP in a region of net ATP catabolism results in selectively high concentrations of AICA riboside and, therefore, ischemic selective effects of the molecule.
• adenosine kinase and adenosine deaminase (ADA) would be only slightly inhibited by a dose of up to 500 mg/kg AICA riboside, but during tissue ischemia, the localized build-up of AICA riboside should cause increased inhibition of adenosine kinase and ADA. This ischemia-specific effect would avoid the deleterious effects of systemic ADA inhibition.
• these AICA riboside prodrugs are useful as antiviral agents. They may be used to treat viral infec- tions such as that caused by HIV. These prodrugs may also be used in. combination with other antiviral agents, and when used in combination, may result in enhanced antiviral activity allowing lower doses and, thus, potentially decreased side effects resulting from those other anti-viral agents.
• prodrugs of AICA riboside having advantageous therapeutic properties.
• the structures of some of these prodrug compounds are depicted in Table I.
• Additonal compounds proposed to be useful as prodrug are depicted in Tables II and III. These prodrug compounds should improve penetration of the blood-brain barrier in comparison with AICA riboside itself because of their longer plasma half-life.
• a prodrug of AICA riboside with the assigned structure: 3'-isobutoxycarbonyl-AICA riboside which appears as Compound 1 of Table 1 ("5-amino-3'-(2-methyl-l-propoxy-carbonyl)-1- ⁇ -D-ribofuranosyl-imidazole-4-carboxamide" or "Prodrug A”) has been found to be particularly good for prolonging the half-life of AICA riboside and in penetrating the gut barrier. It has improved anticonvulsant activity against HTL-induced seizures when compared to AICA riboside. ( Figure l).
• Prodrug A also led to less AICA riboside and, therefore, less ZMP accumulation in the heart than an equimolar dose of AICA riboside and yet had more adenosine production indicating it may have intrinsic (analog) activity.
• 3'-isobutoxycarbonyl-AICA riboside has demonstrated improved. enhancement of adenosine production as compared with the AICA riboside itself. It h ⁇ s an increased half-life as evidenced by the fact that it is cleared and phosphorylated more slowly than AICA riboside. Also, the maximum therapeutic effect of the compound appears to be greater than AICA riboside on a molar basis. This compound, furthermore, exhibits anti-seizure activity in the homocysteine-induced seizure model and increases adenosine production in the myocardial ischemia model. This compound also crosses the gut better than AICA riboside, as there is 5 times more ZMP accumulation in the liver after an equimolar gavage.
• Carbonate esters of AICA riboside are prepared according to the following procedure:
• a 70 mmol portion of AICA riboside is suspended in a mixture of 50/ml N, N-dimethylformamide and 50/ml pyridine and then cooled in an ice-salt bath.
• the appropriate chloroformate 94 mmol, a 20 percent excess
• the reaction mixture is allowed to warm to room temperature over about 1 to 2 hours.
• the progress of the reaction is monitored by TLC on silica gel, eluting with 6:1 methylene chloride:- methanol. Disappearance of AICA riboside indicates completion of the reaction.
• the solvents are removed by evaporation under high vacuum (bath temperature less than 40oC).
• the residue is chromatographed on a silica gel column packed with methylene chloride and is eluted initially with methylene chloride and then with methylene chloride: methanol 95:5. Fractions showing identical (TLC) patterns are pooled and then the eluate is evaporated to give a foam.
• the foam is dried overnight under high vacuum at room temperature.
• the yield of the product carbonate esters is about 45 to 65%. Although the primary product is the 3'-carbonate ester, other product esters are formed.
• a solution of AICA riboside (18.06 g, 70 mmol) in a mixture of pyridine (50/ml) and N,N-dimethylformamide (50/ml) was cooled in an ice-salt mixture.
• an isobutyl chloroformate 11.47g, 94 mmol
• the initial red color of the reaction turned pale yellow in about 40 minutes.
• Methanol (2ml) was added to neutralize unreacted reagents.
• AICA-riboside (12.9 g) was added to a mixture of dry HCl gas (9.0 g) dissolved in dry acetone (115 ml) and absolute ethanol (138 ml). The mixture was stirred at room temperature for two hours. Completion of the reaction was monitored by TLC. The reaction 1 mixture was stirred an additional two hours at room temperature at which time TLC indicated that the reaction was complete. The reaction mixture was poured slowly into an ice-cold mixture of ammonium hydroxide (18 ml) and water (168 ml). The pH of the solution was adjusted to about 8 by adding a few ml of ammonium hydroxide. The reaction was concentrated to 100 ml. The ammonium chloride precipitate was removed by filtration.
• the product was dissolved in about 100 ml methylene chloride and extracted with water (2 ⁇ 100 ml). The organic layer was dried over sodium sulfate and evaporated to obtain a syrup-like product which was carried into the following step for deblocking of isopropylidene group.
• This compound was prepared according to the method described by for the preparation of 2', 3', 5'-tri-o-acetyl-AICA-riboside. (Reference: Suzuki and Kumashiro,
• the yield was 70% and the product had a melting point of 97-100oC.
• the syrupy product was dissolved in 25 ml of a 60% formic acid solution. The resulting mixture was stirred at room temperature for 48 hours. At the end of that time TLC indicated hat the reaction was complete. The reaction mixture was concentrated under high vacuum to give a thick syrup. The syrupy residue was coevaporated with water (2 ⁇ 20 ml) and ethanol (2 ⁇ 25 ml). The product was crystallized from 25 ml ethanol:water (9:1) to give 900 mg of the above-identified compound, melting point 180-181o ⁇ j.
• IR(KBr)cm -1 3000-4000 (NH 2 , OH, etc.), 1725 (v, 1 H-NMR (DMSO-d 6 ), ⁇ ppm: 0.9-1.15 (2t, 6H, 2CH 3 of the two ethyl groups), 2.5 (m, 4H, -CO-CH 2 CH 2 -CO-), 3.1-3.4 (m, 4H, -H 2C C-N-CH 2 -), 4.0 (m, 2H, 5' -CH 2 ), 4.15-4.35 (m, 3H, 2'-CH, 3'-CH and 4'-CH), 5.35 (d, 1H, 1'-CH), 5.5 (2d, 2H, 2'-OH and 3'-OH), 5.8 (br, 2H, 5-NH 2 ), 6.6-6.9 (br.d, 2H, CONH 2 ), and 7.3 (s, 1H, 2-CH).
• the above-identified compound was prepared according to the procedure described in Example 2 for the preparation of 3'-isobutoxycarbonyl-AICA riboside, substituting neopentyl chloroformate for isobutylchloroformate.
• the product was crystallized from hot water to give 8.1 g (yield about 30%) of the above- identified compound as a crystalline solid, melting point 119-121oC.
• IR(KBr)cm -1 3000-4000 (broad peaks, NH 2 , CONH 2 ), 1740-1775 (v -OCOCH 3 and O-COO-neopentyl).
• the above-identified compound was prepared according to the procedure described in Example 14 substituting t-butylisocyanate for n-butylisocyanate in the reaction mixture.
• the above-identified compound was isolated by chromatography using a silica gel column to cjive a yield of approximately 8%.
• the resulting mixture was seeded with a few crystals of 2', 3', 5'-triacetyl AICA riboside.
• the crystalline product formed after 24 hours and was collected by filtration, washed with ice cold ethanol and dried under vacuum (40oC) to give 65.0 g of the aboveidentified product, melting point 128°-130oC.
• the syrupy product obtained after evaporation of the solvent was stirred in hot toluene.
• the toluene was decanted and the product was ground with 150 ml hexane.
• the solid product formed and was collected by filtration, washed and hexane and dried under vacuum to give 11.5 g of the above-identified product.
• the reaction mixture was treated with 5 ml methanol and evaporated under high vacuum.
• the residue was coevaporated twice with 50 ml N,N-dimethylformamide.
• the resulting product was dissolved in 120 ml of 60% formic acid and then allowed to stand at room temperature for 48 hours. Water and formic acid were removed by evaporation under high vacuum.
• the residue was chromatographed on a silica gel column using methylene chloride:- methanol (9:1) as the solvent phase.
• the sticky product obtained after evaporation of solvent was triturated with hot toluene.
• the toluene was decanted.
• the product was ground with hexane.
• the amorphous powder which formed was collected by filtration, washed with hexane, and dried under high vacuum to give 2.7g of the above-identified product.
• mice used were male Swiss Webster mice weighing 21-30 grams (Charles River Breeding Labs, Wilmington, MA). All animals were adapted to the laboratory for at least 5 days prior to use.
• HTL-HCl Thiolactone - HCl
• PTZ Pentylenetetrazol
• Prodrug compounds or AICA riboside when used alone was dissolved in distilled water. All solutions containing Mioflazine (Janssen Pharmaceuticals) were prepared at a final DMSO concentration of 10-15% as were the Dipyridamole (Sigma) solutions. N-ethylcarboxamide adenosine, NECA (Sigma) and Flunitrazepam (Hoffman La Roche) injections were prepared in a final ethanol concentration of 0.2%.
• carrier control solutions of carrier were injected that were matched for both tonicity and solvents to the test solutions. All test and control solutions were injected via a bolus, I.P., using a 27 gauge needle. HTL and PTZ were injected subcutaneously in the upper back of the animal.
• mice were preinjected with either control solution containing only carrier or test solution containing candidate compound (prodrug or AICA riboside) and carrier in groups of 6-8 per test solution or control.
• the seizure inducing composition solution was injected at a specific time interval thereafter (ranging from 15 minutes to several hours, most experiments utilized a 30 minute interval).
• After injection of the seizure inducing composition animals were isolated in separate cages and observed for the onset of a seizure. In most experiments animals were scored as being fully protected from a seizure if they failed to seize for a period 2-3 hours following homocysteine thiolactone (HTL) injections (carrier control latency about 20 minutes) and 1 hour after PTZ administration (carrier control seizure latency of 4 minutes) .
• HTL homocysteine thiolactone
• Seizures noted were either clonic or clonic-tonic in nature and varied in severity from forelimb clonus to full tonic extension of hind limbs and forelimbs. In all experiments the seizure latency was also noted as was the mortality rate in animals having seizures. The overt character of both the PTZ and HTL seizures were quite similar, although the latency of the former was markedly shorter.
• Prodrug compounds of the present invention and AICA riboside were tested for their activity in enhancing the production of adenosine and increasing production of AICA riboside from ZMP in ischemic heart tissue in rats.
• Samples of heart tissue after ischemia were analyzed for nucleoside and nucleotide levels. Samples were measured for adenosine, AICA riboside and ZMP concentrations by HPLC.
• a comparison of adenosine production induced by saline, AICA riboside and Prodrug A (Compound 1 of Table I) is shown in Figure 2.
• the fall in ZMP and quantitatively equivalent rise in AICA riboside level is shown in Figure 3.
• the enhancement of adenosine production by Prodrug A as compared with an equimolar dose of AICA riboside without a corresponding high AICA-riboside"level is tabulated in Table IV.
• Prodrug compounds of the present invention and AICA riboside were tested for their activity in increasing adenosine release in cell culture.
• a human splenic lymphoblast cell line (WI-L2) was used to demonstrate the effect of AICA riboside and prodrugs of the present invention on adenosine release.
• the history and properties of the cell line have been described by Hershfield et al. in Science, Vol. 197, p. 1284, 1977.
• the cell line was maintained in RPMI 1640 cell culture media supplemented with 10% fetal calf serum and 2 mM glutamine and equimolar concentrations of prodrug or AICA riboside and grown for 36 hours in an atmosphere of 5% carbon dioxide in air.
• Fetal bovine serum contains purines and purine metabolizing enzymes; however, and to establish the effect of AICA riboside or prodrug during 2-deoxyglucose exposure, the WI-L2 cells were incubated in RPMI 1640 glucose-deficient medium supplemented with 10% heat-inactivated, dialyzed fetal bovine serum, 2mM glutamine, and 1 ⁇ M deoxycoformycin.
• Catabolism of cellular ATP stores was stimulated by adding 2-deoxyglucose to a final concentration of 10 mM.
• the amount of adenosine released by the cells into the supernatant was determined by mixing 30 microliters of chilled 4.4N perchloric acid with 300 microliters of supernatant and centrifuging the mixtures at 500 ⁇ G for 10 minutes at 4oC.
• Adenosine was evaluated isocratically on a C-18 microBondapak reverse" phase column equilibrated with 4 millimolar potassium phosphate, pH 3.4 :acetonitrile 60% in water (95:5 v/v) buffer-Adenosine elutes at 8-10 minutes and its identity was confirmed by its sensitivity to adenosine deaminase and by spiking with adenosine standards. Continuous monit ⁇ ring was performed by absorbance at 254 and 280 nm. peaks were quantitated by comparison with high pressure liquid chromatography analysis of suitable standards.
• Figure 4 shows the effect of 36 hour pretreatment with AICA riboside or Prodrug A on enhancement of adenosine release from lymphoblasts.
• AICA riboside was administered to Sprague-Dawley rats at a dose of 250 mg/kg or 500 mg/kg, prodrug compounds of the present invention were administered at an equal molar dose.
• the tissue samples obtained were liver, heart, .brain and whole blood. After initial freezing in liquid nitrogen, the tissue samples were extracted with trichl ⁇ roacetic acid and neutralized with alamine freon. The t ⁇ !ssue samples were evaluated by HPLC on a Whatman Paatsil-10 (SAX) column for nucleosides and bases as described in Example 6.
• SAX Whatman Paatsil-10
• Figures 5(a) and (b) show ZMP concentrations in rat liver at doses of a molar equivalent of 250 mg/kg and 500 mg/kg AICA riboside.
• mice Male mice (Swiss-Webster) were injected IP with the indicated treatment. The mice were fasted for 120 minutes before treatment. Ribose and AICA riboside were formulated in saline. Glucose levels were measured on serum (heparinized blood centrifuged at 10,000 ⁇ g for ten minutes). Glucose levels were measured one hour after AICA riboside administration. Results are reported in Figure 6.
• AICA riboside either 2 ml/kg (100 mg/kg) or 4 ml/kg (200 mg/kg). Blood was obtained by venipuncture before AICA riboside administration and two hours post-administration.
• AICA Riboside Effect of AICA Riboside on Plasma Glucose Levels in Humans Healthy male volunteers were given a 30-minute intravenous infusion of AICA riboside at doses of 25 mg/kg, 50 mg/kg or 100 mg/kg.
• Plasma glucose levels were monitored over a four hour period during and following the 30 minute infusion. Plasma glucose was measured by clinical chemistry autoanalyzer. The onset of the serum glucose lowering effect was evident by the end of the AICA riboside infusion period and plasma glucose reached a nadir approximately 30 minutes after the AICA riboside infusion was stopped. Recovery to euglycemic levels was complete by about three hours. Results are shown in Figure 8.
• mice were treated with saline (as a control) or 750 mg/kg of AICA riboside administered intra- peritoneally, six animals per group. The mice were sacrificed one hour post-administration. The livers were removed and extracted. Liver glycogen was determined by the method of Dubois, et al., Anal. Chem. 28:350-356 (1956). Glucose was measured by the hexokinase method (See Example K). Results are reported in Figure 9.
• AICA riboside 100, 250 or 500 mg/kg or saline (as a control) was administered intraperitoneally to rats. Sixty minutes after AICA riboside administration, the rats were sacrificed by cervical dislocation. Blood glucose was determined spectrophotometrically measuring O.D. at 340 nm by the hexokinase method using the glucose SR Reagent (Medical Analysis Systems, Inc.) Blood lactate and pyruvate were determined spectrophotometrically measuring O.D. at 340 nm using lactate dehydrogenase in the presence of excess NAD or NADH, respectively. Values were expressed as mean + S.E.M. Results are reported in Figures 10A to 10D.
• AICA riboside-induced reduction in blood glucose with hepatic ZMP in the mouse was investigated.
• AICA riboside (either 100 or 500 mg/kg) was administered intravenously by tail vein injection to mice which had been fasted for four hours. At a time of 2, 5, 10, 30 or 120 minutes post-administration, the mice were sacri- ficed by cervical dislocation. Blood glucose was measured spectrophotometrically, measuring O.D. at 340 nm, by the hexokinase method using the glucose SR Reagent (Medical Analysis Systems, Inc.).
• liver Portions of liver (0.2 to 0.3 g) were freeze clamped in situ, homogenized and, following centrifugation, the neutralized supernatant was analyzed by ion-exchange HPLC. Values were expressed as means + S.E.M. Results are reported in Table 11.
• mice Male mice (Swiss Webster) were given equimolar amounts of either saline, AICA riboside, or compounds C1 or 10 of Table I orally. Blood glucose levels were measured one hour after administration by the glucose strip method (Chemstrip B.G.). Results are reported in Figure 14.
• mice were given the indicated dose (100, 200 or 400 mg/kg) of the adenosine kinase inhibitor, 5'-amino-5'-deoxyadenosme, or saline (as a control) intraperitoneally.
• adenosine kinase inhibitor 100, 200 or 400 mg/kg
• 5'-amino-5'-deoxyadenosme or saline (as a control) intraperitoneally.
• saline as a control mice were given a 75 mg/kg dose of pentylenetetrazole (PTZ) and the seizure frequency observed. Results are reported in Figure 15.
• PTZ pentylenetetrazole
• Rats were made diabetic by treatment with streptozocin (50 mg/kg IV) and then treated with either saline or
• AICA riboside 500 mg/kg, twice a day for 22 days.
• Plasma triglyceride levels were analyzed 18 hours after the last injection of AICA riboside using the Sigma Procedure #334 Assay Kit (coupled assay employing lipase, glycerokinase, pyruvate kinase and lactate dehydrogenase) which measures decreases in OD 340 over time (NADH disappearance).
• Sigma Procedure #334 Assay Kit coupled assay employing lipase, glycerokinase, pyruvate kinase and lactate dehydrogenase
• Plasma concentrations of AICA riboside in dogs were determined by HPLC following oral administration of 50 mg/kg AICA riboside and the (molar) equivalent amount of 50 mg/kg AICA riboside or one of two prodrugs, compounds 10 and 17 of Table I. The compounds were administered in solution in PEG 400:water (1:1). Results are shown in Figure 18. A different prodrug. Compound 22 of Table I, was administered in solid form in a capsule (50 mg/kg). Results are shown in Figure 20. Plasma concentration of AICA riboside was determined according to: Dixon, R., et al., "AICA riboside: Direct quantitation in ultra-filtrate of plasma by HPLC," Res. Commun. Chem. Path. Pharm., in press (1989).
• mice were made diabetic by low dose Streptozotocin treatment (40 mg/kg/day for 5 days followed by a 10-day incubation period). These diabetic mice, 11 per group, were treated with the indicated dose of AICA riboside or saline in an IP bolus of 1 ml/100 g body weight. The animals were exsanguinated 1.5 hours post-administration (of AICA riboside or saline). The plasma was isolated by centrifugation and analyzed for glucose by the hexokinase/glucose-6-phosphate dehydrogenase spectrophoto-metric method (see Example K). Normoglycemic levels were determined from saline-treated nondiabetic mice by the same protocol. Values were expressed as mean ⁇ sem. Results are reported in Figure 21. Example U
• Rats made diabetic with Streptozotocin 60 mg/kg, 5 days post-treatment), 9 per group, were treated twice daily with 500 mg/kg AICA riboside or with physiological saline via injection IP, except for days 6, 13 and 20 when a single 750 mg/kg dose was administered and except for days 7, 14 and 21 when no treatment was given.
• Blood was drawn by tail bleeds, two hours post-injection, on the days indicated, analyzed for glucose using Chemstrip bG glucose reagent strips and an Accuchek II blood glucose monitor (both from Boehringer Manheim). Data was calculated as percent of pretreated levels and expressed as mean ⁇ sem. Results are reported in Figure 22.
• Rats made diabetic with Streptozotocin (60 mg/kg, 5 days post treatment) were treated with either 2 ⁇ 500 mg/kg/day AICA riboside or 0.9% saline twice a day for three weeks. Eighteen hours after the last treatment the livers were removed. Livers from the treated rats and from native rats were homogenized in 20 ⁇ M potassium phosphate buffer (pH 7.4) with 100 ⁇ M EDTA and 100 ⁇ M dithiothreitol and then centrifuged for 20 minutes at 45,000 ⁇ g.
• FDPase activity was assayed both in this native form and following passage of the supernatant over a sephadex G25 column by the method of Marcus et al (Methods in Enzymology 9J): 352-356 (1982)). Protein concentrations were determined by the Bradford method (Anal. Biochem. 72.:248 (1976); Anal. Biochem. 86:142 (1978)). Enzyme activity per mg protein was expressed as mean ⁇ sem. Results are shown in Figure 24.
• Liver samples (from the indicated species) were homogenized in 20 mM potassium phosphate buffer (pH 7.4) with 100 ⁇ M EDTA and 100 ⁇ M dithiothreitol .
• the liver homogenates were centrifuged at 45,000 x/g.
• the supernatants were passed over a sephadex G25 column and assayed for FDPase activity by the method of Marcus et al (Methods in Enzymology 9j0: 352-356 (1982)) in the presence of ZMP over a range of concentration and in the absence of ZMP.
• the IC50 value was defined as the concentration of ZMP, which inhibited 50 percent of the baseline FDPase activity under the assay conditions. Results are shown in Table VII.
• mice which had been fasted for 6 hours were given either an IP injection of 500 mg/kg AICA riboside or 0.9% saline.
• the animals were sacrificed 1.5 hours post- injection; their livers were removed and extracted into iced perchloric acid.
• the extracts were neutralized and analyzed for fructose 1,6-diphosphate by the method of Shrinivas et al (Biochem J. 262: 721-725 (1989)). Results are shown in Figure 25.
• mice were treated either with vehicle, 5 mg/kg glyburide (an oral hyperglycemic agent) administered orally or 600 mg/kg AICA riboside adminis tered IP. Either three hours post-administration or at the time of hypoglycemic seizure, whichever came first, blood was taken. The serum was isolated by centrifugation and analyzed for glucose levels by the hexokinase/glucose- 6-phosphate dehydrogenase spectrophotometric assay (see Example K) . Drug group values were expressed as percent of vehicle levels. Results are shown in Figure 26.
• Sprague-Dawley rats (200g each) made diabetic with Streptozotocin (55 mg/kg, 4 days post-treatment) were anesthetized with diethyl ether. After anesthetizing, an incision was made and a cannula of silastic medical grade tubing (0.020 inch I.D/0.037 inch O.D.) was inserted into the right jugular 5 mm rostral to the clavicle and extended 20 mm toward the heart. The cannula was anchored and exteriorized through the back of the neck, filled with heparized saline (500 U/ml) and tied off.
• silastic medical grade tubing 0.020 inch I.D/0.037 inch O.D.
• AICA riboside after oral administration of either AICA riboside or one of the AICA riboside prodrugs of the present invention was evaluated in dogs. Plasma concentrations of AICA riboside and intact prodrug were measured using HPLC. (See Dixon, R., et al., Res. Commun. Chem. Path. Pharm. 65:405-408 (1989)). Bioavailability of AICA riboside was evaluated in terms of the time required to reach maximum plasma concentration (Tmax), the maximum concentration achieved
• AICA riboside i.v. - - 8.3 100 AICA riboside (oral) 0.75 1.1 0.9 11 Cl * ( 2', 3', 5'-Triacetyl-

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