A number of esters and amides of the anti-HIV nucleotide analogue 9-[2-(phosphonomethoxy)-ethoxy]adenine (1) have been synthesized as potential prodrugs and evaluated for oral bioavailability in mice. Dialkyl esters 17-20 were prepared via a Mitsunobu coupling of alcohols 8-11 with 9-hydroxypurine 12 whereas (acyloxy)alkyl esters 25-33 and bis-[(alkoxycarbonyl)methyl] and bis(amidomethyl) esters 34-39 were obtained by reaction of 1 with a suitable alkylating agent. Phosphonodichloridate chemistry was employed for the preparation of dialkyl and diaryl esters 42-65, and bis(phosphonoamidates) 66 and 67. Following oral administration to mice, most of the dialkyl esters 17-20 were well-absorbed and then converted to the corresponding monoesters, but minimal further metabolism to 1 occurred. Bis[(pivaloyloxy)methyl] ester 25 displayed an oral bioavailability of 30% that was 15-fold higher than the bioavailability observed after dosing of 1. Methyl substitution at the alpha carbon of the bis[(pivaloyloxy)methyl] ester 25 (33) increased the oral bioavailability of 1 to 74%. Some of the diaryl esters also showed improved absorption properties in comparison with that of 1. In particular, the crystalline hydrochloride salt of diphenyl ester 55 was well-absorbed and efficiently converted to the parent compound with an oral bioavailability of 50%. On the basis of these results as well as the physicochemical properties of the prodrugs and their stability in mouse duodenal contents, the hydrochloride salt of diphenyl ester 55 was identified as the preferred prodrug of 1.

SummaryAcyclic acetal derivatives of the selective antiherpesvirus agent 9-(3-hydroxypropoxy) guanine (BRL44385) and of its 2-aminopurine congener (BRL46720) have been prepared and evaluated in mice for oral delivery of BRLh4385. Guanine derivatives (6 a-c) were prepared~. Mitsunobu condensation of an alcohol with a 9-hydroxy-6-methoxypurine . Synthesis of derivatives of 2-aminopurine (tOa-d) was achieved by hydrogenolysis of 9-alkoxy-6-chloropurines, which were obtained either by reaction of an alkoxyamine with 4,6-dichloro-2,5-diformamidopyrimidine and subsequent ring closure or by Mitsunobu condensation of an alcohol with a 6-chloro-9-hydroxypurine. Following oral administration, 2-amino-9-[3-(isopropoxymethyl)propoxy]-purine (tob, BRL 55792) was very well absorbed and provided high and prolonged concentrations of BRL44385 in the blood. In a cutaneous HSV-1 infection in the ear pinna of mice, orally dosed BRL55792 was at least 3-fold more potent than both BRL44385 and Acyclovir in reduction of lesion severity.