PROTON MAGNETIC-RESONANCE STUDY OF THE CONFORMATIONS OF 3',5'-O-(DI-TERT-BUTYLSILANEDIYL) NUCLEOSIDES

The solution conformations of nine 3',5'-O-(di-tert-butylsilanediyl) n ucleosides, new sila analogues of cyclic nucleotides, were studied by proton NMR spectroscopy. The furanose rings of all the compounds studi ed are forced to take on the C-3'-endo conformation by the 3',5'-cycli zation. The conformations at the glycosidic bond of the adenosine and deoxyadenosine derivatives were determined as mixtures of syn and anti conformations by the DESERT method; the fractions of anti conformatio n for these derivatives were 0.58 and 0.41, respectively.