Homonucleoside phosphonic acid-I: Ageneral synthesis of isosteric phosphonate analogs of nucleoside 3'-phosphates

A general synthetic route to 3'-deoxy-3'-dihydroxyphosphinylmethyl ribonucleosides 3 the isosteric phosphonate analogs of nucleoside 3'-phosphates, is described. This involved alkylation of 1,2;5,6-di-O-isopropylidene-α-D-ribo-hexofuranose-3-ulose 7) with tetraethyl methylenediphosphonate 6, followed by stereoselective catalytic reduction and cleavage of C₆ to generate 3-deoxy-3-diethoxyphosphinylmethyl-1,2-O-isopropylidene-α-D 12a. Benzoylation followed by acetolysis then generated the key crystalline intermediate 1,2-di-O-acetyl-5-O-benzoyl-3-deoxy-3-diethoxyphosphinylmethyl-β-D-ribofuranose 13, This compound, or the related glycosyl chloride, was condensed with several purine and pyrimidine bases and all protecting groups were removed by mild alkaline treatment via a series of intramolecular cyclizations and hydrolysis. In this manner the phosphonate analogs of nucleoside 3'-phosphates derived from adenine, 6-dimethylaminopurine, uracil, thymine, and cytosine were prepared.