Synthesis and Evaluation of 2-Amino-9-(3-hydroxymethyl-4-alkoxycarbonyloxybut-1-yl)purines as Potential Prodrugs of Penciclovir

A series of 2-amino-9-(3-hydroxymethyl-4-alkoxycarbonyloxybut-1-yl)purines (4−10) and 2-amino-9-(2-(2-oxo-1,3-dioxan-5-yl)ethyl)purine (1) were synthesized as potential prodrugs of penciclovir and evaluated for their oral penciclovir bioavailability in mice and rats. Treatment of 2-(2-benzyloxyethyl)propane-1,3-diol (11) with 1,1‘-carbonyldiimidazole in THF followed by hydrogenolytic removal of the benzyl group of the resulting cyclic carbonate 12 gave 5-(2-hydroxyethyl)-1,3-dioxan-2-one (13). Mesylation of the alcohol 13 and then a coupling reaction of the resulting mesylate 14 with 2-amino-6-chloropurine using anhydrous Cs2CO3 in DMF afforded 2-amino-6-chloro-9-(2-(2-oxo-1,3-dioxan-5-yl)ethyl)purine (16) after purification by flash column chromatography on silica gel using EtOAc/MeCN/Et3N as eluent. Hydrogenation of the 6-chloro cyclic carbonate 16 followed by a ring-opening reaction of the 6-deoxy cyclic carbonate 1 in a mixture of an appropriate alcohol and CHCl3 using activated SiO2 as a Lewis acid a...