Synthesis, in Vitro Biological Evaluation and Oral Bioavailability of 9-[2-(Phosphonomethoxy)Propyl]Adenine (PMPA) Prodrugs

Abstract

Potentially orally bioavailable prodrugs of the antiretroviral agent 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) were evaluated. Alkyl methyl carbamates were synthesized by alkylation of PMPA with the corresponding alkyl chloromethyl carbonate and N-alkyl chloromethyl carbamate reagents. The prodrugs were evaluated for in vitro antiviral activity in addition to chemical and enzymic stability. The inhibition of human immunodeficiency virus type 1 (HIV-1) strain IIIB replication in MT-2 cells by the carbonate prodrugs was found to be 2.5-500-fold increased compared to PMPA. The alkyl methyl carbonates, except t-butyl methyl carbonate, had reasonable chemical stability at pH 2.2 and 7.4, but were rapidly converted to the corresponding monoester of PMPA in the presence of dog plasma. The alkyl methyl carbamate prodrugs such as N-t-butyl methyl carbamate were found to have high stability in vitro. Based on its chemical stability and good oral bioavailability, bis(POC)PMPA (isopropyl methyl carbonate) was chosen as a clinical candidate.