Pradefovir: a prodrug that targets adefovir to the liver for the treatment of hepatitis B.

Adefovir dipivoxil, a marketed drug for the treatment of hepatitis B, is dosed at submaximally efficacious doses because of renal toxicity. In an effort to improve the therapeutic index of adefovir, 1-aryl-1,3-propanyl prodrugs were synthesized with the rationale that this selectively liver-activated prodrug class would enhance liver levels of the active metabolite adefovir diphosphate (ADV-DP) and/or decrease kidney exposure. The lead prodrug (14, MB06866, pradefovir), identified from a variety of in vitro and in vivo assays, exhibited good oral bioavailability (F = 42%, mesylate salt, rat) and rate of prodrug conversion to ADV-DP. Tissue distribution studies in the rat using radiolabeled materials showed that cyclic 1-aryl-1,3-propanyl prodrugs enhance the delivery of adefovir and its metabolites to the liver, with pradefovir exhibiting a 12-fold improvement in the liver/kidney ratio over adefovir dipivoxil.

Adenosine kinase inhibitors. 4. 6,8-Disubstituted purine nucleoside derivatives. Synthesis, conformation, and enzyme inhibition.

6,8-Disubstituted purine nucleosides were synthesized and evaluated as adenosine kinase inhibitors (AKIs). A method was developed to selectively substitute arylamines for halogens at C6 and C8 which utilizes alkali salts of arylamino anions. Regioselectivity was found to be counterion dependent. Potassium and sodium salts add selectively to C6 of 6-chloro-8-iodo-9-(2,3,5-tris-O-tert-butyldimethylsilyl-beta-d-ribofuranosyl)purine (7a) while lithium salts add to C6 and C8 positions. Differential 6,8-bisarylamin-N,N'-diylpurine nucleosides such as 8-anilin-N-yl-6-indolin-N-yl-9-(beta-d-ribofuranosyl)purine (10b) can be prepared by employing stepwise reactions of potassium and then lithium salts of different arylamino anions followed by fluoride ion-induced desilylation. Other C8-substituted compounds were prepared by way of either C8 lithiation chemistry or palladium cross-coupling reactions. Several of these compounds were potent AKIs (e.g. 10b, AK IC(50) = 0.019 microM) and are more potent than the previous best purine-based AKI 5'-deoxy-5'-aminoadenosine (AK IC(50) = 0.170 microM). AK inhibitory potency was greatest for those compounds with (1)H NMR evidence of a predominant anti glycosyl bond conformation, whereas most analogues adopt a syn conformation because of steric repulsions between the C8 substituent and the ribose group. The inhibitors are proposed to bind in the anti conformation with the hydrophobic C6 and C8 substituents contributing to AK affinity in a manner similar to the C4 and C5 aryl substituents of the potent diaryltubercidin nucleoside inhibitor series.

Adenosine kinase inhibitors. 5. Synthesis, enzyme inhibition, and analgesic activity of diaryl-erythro-furanosyltubercidin analogues.

Adenosine is an endogenous neuromodulator that when produced in the central and the peripheral nervous systems has anticonvulsant, anti-inflammatory, and analgesic properties. However, efforts to use adenosine receptor agonists are plagued by dose-limiting cardiovascular side effects. As an alternative, we explored the use of adenosine kinase inhibitors (AKIs) as potential antiseizure agents and demonstrated an adenosine receptor mediated therapeutic effect in the absence of overt cardiovascular side effects. These activities were associated with elevation of extracellular adenosine concentrations due to inhibition of AK in a site and event specific manner. Several tubercidin based AKIs, including the ribo- and lyxo-furanosyltubercidin analogues as well as the newly discovered erythro-furanosyltubercidin analogues, designed to prevent 5'-O-phosphorylation and associated toxicities, were tested for their analgesic activity in the rat formalin paw model. Described herein are the synthesis, enzyme inhibition structure-activity relationships (SARs) of erythro-furanosyltubercidin analogues, and SARs of analgesic activity of various classes of AKIs. Also reported is the characterization of a lead AKI, 19d (GP3966), an orally bioavailable compound (F% = 60% in dog) which exhibits broad-spectrum analgesic activities (ED50 < or = 4 mg/kg, per os) that are reversible with an adenosine receptor antagonist (theophylline).