Electrophile-promoted addition of hydroxymethylphosphonate to 4′,5′-didehydronucleosides: a way to novel isosteric analogues of 5′-nucleotides

An electrophile-promoted addition of dialkyl-hydroxymethylphosphonate to the protected 4′,5′-didehydronucleosides resulted in an epimeric mixture of 4′-dialkylphosphonomethoxy derivatives of 2′,5′-dideoxynucleosides, novel analogues of 2′-deoxynucleoside 5′-monophosphates. Several types of electrophiles (pyridinium tosylate, NIS, NBS, MCPBA and others) were evaluated in addition reactions with 4′,5′-didehydrothymidine. Out of them, pyridinium tosylate was found to have a practical usefulness in these transformations. Its use has led to the preparation of a series of 4′-phosphonomethoxy derivatives of common 2′-deoxynucleosides. On biological screening, these free phosphonic acids exerted no significant cytostatic or antiviral activity.