Alternative synthesis of 9-{3-[(diisopropoxyphosphoryl)methoxy]-2-hydroxypropyl}adenine and its free phosphonates substituted at the C-8 position of purine base

Abstract

For its high therapeutic effect, (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine (HPMPA) is an important member of a class of acyclic nucleoside phosphonates (ANPs). Although its constitutional isomer, 9-[2-hydroxy-3-(phosphonomethoxy)propyl]adenine (iso-HPMPA), exhibits no antiviral activity, our general interest in C-8 substituted adenine ANPs led us to prepare certain iso-HPMPA derivatives modified at the C-8 position of adenine. Novel alkylating agent, diisopropyl {[2-(tetrahydro-2-pyranyl)oxy-3-tosyloxypropoxy]methyl}phosphonate (9), was prepared by procedure starting from allyl alcohol (4). 9-{3-[(Diisopropoxyphosphoryl)methoxy]-2-hydroxypropyl}adenine (12) was prepared by alkylation of adenine with the alkylating agent 9 followed by acid hydrolysis, although elimination by-product 9-{3-[(diisopropoxyphosphoryl)methoxy]prop-1-enyl}adenine (11) predominated in the reaction mixture. Bromination of the compound 12 gave 8-bromoadenine derivative 13 quantitatively. Nucleophilic substitutions of the bromine atom of compound 13 with N- and O-nucleophiles, followed by phosphonate deprotection, afforded the free phoshonic acids 15–18.