Higher Oligomers of ppp(A2′p)n together with (A2′p)nA, (A2′p)2A3′OCH3, (A2′p)2A2′,3′CH2, (A2′p)2dA, (dA2′p)2dA, their 5′‐monophosphates and 5′‐S‐methylphorothioates have been investigated for relative stability and biological activity in mouse and human cells and mouse, human, and rabbit cell‐free systems. The oligomers from trimer to heptamer inhibited protein and DNA synthesis when introduced into intace mouse cells and activated the ppp(A2′p)n A‐dependent RNase at below nanomolar concentrations in mouse cell extracts.
The 5′‐diphosphates pp(A2′p)2A and corresponding analogues were active both in cell‐free systems and on introduction into intact cells. The exception to this was the all 3′‐deoxyadenosine analogue pp(dA2′p)2 dA which failed to activate the ppp(A2′p)nA‐dependent nuclease in the mouse L and human (Daudi and HeLa) cell extracts tested. Of the active analogues the 3′‐OCH3 appeared to be the most stable in the cells and systems employed. On the other hand the non‐phosphorylated ‘core’ (A2′p)2A and its 3′‐sunstituted analogues were inactive in mouse L and Ehrlich acites tumours cell‐free systems and had to effect on intact (non‐permeabilised) 3T3 cells.
The 5′‐monophoshate, p(A2′p)2A, can act as an inhibitor of ppp(A2′p)nA in mouse cell‐free systems [Torrence, Imai and Johnston (1981) Proc. Natl Acad. Sci. USA, 78, 5993‐59997]. Here in intact mouse L cells or extracts from interferon‐treated human (Daudi) cells, however, it mimicked the action of ppp(A2′p)2A, possibly through conversion to the 5′‐diphosphate or 5′‐S‐methylphosphorothioate derivatives of the 3′‐substituted analogues are both more stable to exonucleolytic cleavage and unlikely to be converted to the 5′‐diphosphated or 5′‐triphosphates. They are analogue inhibitors of ppp(A2′p)nA in mouse L cell extracts. How widely they will be effective in a variety of cell‐free systems and intact cells remains to be established.
The 5′‐diphosphate pp(A2′p)2A and corresponding analogues were not equally active, nor was the CH3Sp(A2′p)2A2′,3′CH2 equally effective as an analogue inhibitor, in different cell‐free systems. This emphasises the apparent differences in the properdties of the ppp(A2′p)nA‐dependent RNases from different sources. Accordingly, in looking for a generally effective analogue inhibitor of ppp(A2′p)2A its activity in a variety of extracts should be tested and in any search for further analogues for potential clincial use human cells and extracts should be employed.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.