Ribonucleoside cyclic 3′,5′-phosphoramidates: synthesis, stereochemistry, and conversion into ribonucleoside cyclic 3′,5′-phosphorothioates and -[18O]phosphates

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Abstract
Base- and O2′-protected nucleoside cyclic 3′,5′-phosphates (1) react with aniline in the presence of triphenylphosphine–carbon tetrachloride to give the nucleoside cyclic 3′,5′-phosphoranilidates (2), which after separation into individual diastereoisomers are converted in stereoretentive manner into the corresponding nucleoside cyclic 3′,5′-phosphorothioates (3). Isotopomers of adenosine cyclic 3′,5′-[18O] phosphates (9a) are prepared via two independent routes: (a) reaction of adenosine cyclic 3′,5′-phosphoranilidates (2a) with sodium hydride–[18O]benzaldehyde (retention) or (b) acid-catalysed hydrolysis of adenosine cyclic 3′,5′-N,N-dimethylphosphoramidates (10a)(inversion). Adenosine cyclic 3′,5′-phosphoranilidothioates (Sp)-(23) and (Rp)-(23), prepared via cyclisation of the corresponding 5′-[O-(4-nitrophenyl)phosphoranilidothioates](22), have been converted into P-achiral adenosine cyclic 3′,5′-phosphorodithioate (26).