Boranophosphorothioate, 3 ,5 -cyclic

Example 35 Li and Shaw [69] in their synthesis of nucleoside 3, 5 -cyclic boranophosphorothioate have used 3, 5 cyclic phosphoroamidite. 

Shaw has reported the first syntheses of thymidine- and 2 -deoxy-5-fluorouridine - 3, 5 - cyclic boranophosphorothioate (103a,b). These analogues, displaying increased lipophilicity, were prepared from a key intermediate, a cyclic phosphoramidite obtained by heating a thoroughly degassed HMPA solution of the nucleoside. This phosphoramidite was then converted to a cyclic phosphite triester in the presence of 4-nitrophenol and 5-ethylthio-lH-tetrazole, and converted to the boranated complex in situ. The cyclic boranophosphite was then converted to the 3, 5 -cyclic boranophosphorothioate. ... 

Shaw reported the synthesis of P-tyrosinyl-(P-0)-5-P-nucleosidyl boranophos-phates (190a,b) obtained in a one-pot synthetic procedure via a phosphoramidite and that of the nucleoside 3, 5 -cyclic boranophosphorothioates (191a,b) prepared from a cyclophosphoramidite intermediate. The cyclophosphoramidite, obtained by heating the nucleoside with HMPA was transformed to the phosphite triester by reaction with 4-nitrophenol in the presence of 5-ethylthio-l//-tetrazole. The boranophosphite was oxidized with Li2S after boronation with BH3.SMe2. 

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See also in sourсe #XX -- [ ]

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