The first potent, specific, and cell-penetrable AMP deaminase (AMPDA) inhibitors were discovered through an investigation of 3-substituted 3,6,7,8-tetrahydroimidazo[4,5-d][1,3]diazepin-8-ol analogues. Inhibition constants for the most potent inhibitors were 105-fold lower than the K M for the substrate AMP. High affinity required the presence of both the 8-hydroxyl and the 3-substituent and is postulated to arise from a cooperative interaction that reduces binding entropy costs and enables the diazepine base to adopt a binding conformation that mimics the transition-state (TS) structure. The high specificity of the inhibitor series for AMPDA relative to other AMP-binding enzymes (>105) is attributed in part to the diazepine base which favors interactions with residues used to stabilize the TS structure and precludes interactions typically used by AMP-binding enzymes to bind AMP. In contrast, discrimination between AMPDA and adenosine deaminase (ADA), two enzymes postulated to stabilize a similar TS structure, is highly dependent on the 3-substituent. Replacement of the ribose group in the potent ADA inhibitor coformycin (K i (ADA) = 10-11 M vs K i (AMPDA) = 3 × 10-6 M) with 3-carboxy-4-bromo-5,6,7,8-tetrahydronaphthylethyl led to a >1010-fold change in specificity (K i (ADA) > 10-3 M vs K i (AMPDA) = 2 × 10-9 M). Inhibitors from the series readily penetrate cells and inhibit intracellular AMPDA activity. Incubation of isolated rat hepatocytes with AMPDA inhibitors had no effect on secondary metabolite levels during normoxic conditions but led to increased adenosine production and adenylate sparing under conditions that induce net ATP breakdown. These results suggest that inhibitors of AMPDA may represent site- and event-specific drugs that could prevent or attenuate ischemic tissue damage resulting from a stroke or a heart attack.

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A series of N3-substituted coformycin aglycon analogues are described that inhibit adenosine 5'-monophosphate deaminase (AMPDA) or adenosine deaminase (ADA). The key steps involved in the preparation of these compounds are (1) treating the sodium salt of 6, 7-dihydroimidazo[4,5-d][1,3]diazepin-8(3H)-one (4) with an alkyl bromide or an alkyl mesylate to generate the N3-alkylated compound 5 and (2) reducing 5 with NaBH(4). Selective inhibition of AMPDA was realized when the N3-substituent contained a carboxylic acid moiety. For example, compound 7b which has a hexanoic acid side chain inhibited AMPDA with a K(i) = 4.2 microM and ADA with a K(i) = 280 microM. Substitution of large lipophilic groups alpha to the carboxylate provided a moderate potency increase with maintained selectivity as exemplified by the alpha-benzyl analogue 7j (AMPDA K(i) = 0.41 microM and ADA K(i) > 1000 microM). These compounds, as well as others described in this series of papers, are the first compounds suitable for testing whether selective inhibition of AMPDA can protect tissue from ischemic damage by increasing local adenosine concentrations at the site of injury and/or by minimizing adenylate loss.

4-(Phenylamino)-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine 1 and related compounds known as "diaryltubercidin" analogues are potent inhibitors of adenosine kinase (AK) and are orally active in animal models of pain such as the rat formalin paw model (GP3269 ED50= 6.4 mg/kg). However, the utility of this compound class is limited by poor water solubility that can be attributed to the high energy of crystallization caused by stacking of the parallel C4 and C5 aryl rings in the solid state (compound 1 and GP3269 each with pH 7.4 solubility <0.05 microg/mL). To increase water solubility, the hydrophobic C4-phenylamino substituent was replaced with a more hydrophilic group, glycinamide. This modification resulted in improved water solubility while retaining AK inhibition potency. Analogues were studied where changes in the glycinamide moiety were combined with changes to the base and sugar. A lead compound, 4-N-(N-cyclopropylcarbamoylmethyl)amino-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (16c) (IC50= 3 nM and water solubility = 32 +/- 9 microg/mL at pH 7.4), was further characterized in biological assays. Compound 16c exhibited strong oral efficacy in the rat formalin paw model (ED50 of 2.5 mg/kg). In the most advanced assay, 16c was found to inhibit bradykinin-induced licking in marmoset monkeys with an ED50 estimated at 0.9 mg/kg without producing evidence of side effects such as ataxia, sedation, and emesis at this dose. However, lethal toxicity in the rat formalin paw model occurred with high doses of 16c, and further work on this series was discontinued.

Alkylation of 4-methoxy-1 H-pyrazolo[3,4- d]pyrimidine (1b) with iodomethane in THF using NaHMDS as base selectively provided N2-methyl product 4-methoxy-2-methyl-2 H-pyrazolo[3,4- d]pyrimidine (3b) in an 8/1 ratio over N1-methyl product (2b). Interestingly, conducting the reaction in DMSO reversed selectivity to provide a 4/1 ratio of N1/N2 methylated products. Crystal structures of product 3b with N1 and N7 coordinated to sodium indicated a potential role for the latter reinforcing the N2-selectivity. Limits of selectivity were tested with 26 heterocycles which revealed that N7 was a controlling element directing alkylations to favor N2 for pyrazolo- and N3 for imidazo- and triazolo-fused ring heterocycles when conducted in THF. Use of H-detected pulsed field gradient-stimulated echo (PFG-STE) NMR defined the molecular weights of ionic reactive complexes. This data and DFT charge distribution calculations suggest close ion pairs (CIPs) or tight ion pairs (TIPs) control alkylation selectivity in THF and solvent-separated ion pairs (SIPs) are the reactive species in DMSO.