Configurational determination and conformational properties of diastereomeric nucleoside-phosphorothioates

Synthesis and structural study of variously oxidized diastereomeric 5'-dimethoxytrityl-thymidine-3'-O-[O-(2-cyanoethyl)-N,N-diisopropyl]-phosphoramidite derivatives. Comparison of the effects of the P=O, P=S, and P=Se functions on the NMR spectral and chromatographic properties

R(P)- and S(P)-diastereomers of 5'-dimethoxytrityl-thymidine-3'-O-[O-(2-cyanoethyl)-N,N-diisopropyl]-phosphoramidite (T-CED) were separated by silica gel chromatography. Oxidation of both isomers with H(2)O(2), elemental sulfur and selenium, respectively, resulted in the corresponding oxidized analogues in nearly quantitative yields. All reactions were found to proceed with retention of P-configuration. This was confirmed by thorough NMR analysis which, in addition, aimed to study the spectral properties of the diastereomers with special respect to differences in the heteroatom effect of the O, S and Se atoms, double-bonded to the phosphorus, on the vicinal carbon-phosphorus couplings. It was found that the changes in the DeltaJ (=(3)J(P,C4') - (3)J(P,C2')) values were basically induced by the electronegativity of the heteroatoms, rather than differences in the rotational preferences about the C3'-O3' bond. The impact of the benzene solvent on the above couplings is also discussed. The effect of these heteroatoms on the chromatographic (normal and reverse phase HPLC) behavior of the compounds was also investigated and the reverse phase HPLC profiles showed an unambiguous correlation between the electronegativity of the heteroatoms and the chromatographic mobility of the analogues.

13C-31P couplings in the study of conformational properties of some diastereomeric nucleoside-3'-thiophosphate derivatives

Synthesis and stereochemical characterization of enantiomerically pure nucleoside-3'-phosphorothioate esters and salts are reported. Vicinal carbon phosphorus couplings reflect different predominance of the epsilon conformation in the isomeric (Rp and Sp) esters, while for the salts the epsilont conformation prevails in both stereoisomers. The influence of solvent and temperature on the conformational preferences is also described.

Solution structure of diastereomeric thymidine 3'-O(N,N-diisopropyl-O-beta-cyanoethyl-phosphoramidothioate)s by NMR spectroscopy

The conformational properties of a diastereomeric nucleoside-phosphorothioate pair is reported as reflected by different NMR parameters. Configurational assessment is based partly on the different NOE (nuclear overhauser enhancement) effects of the individual isomers and on the trends observed in other NMR parameters. Vicinal carbon-phosphorus couplings reflect the predominance of the epsilon(-) conformation for the Sp isomer and the epsilon(t) conformation for the Rp isomer. The effects of solvent and temperature on these vicinal couplings are described and the results are interpreted in terms of conformational shift towards the preferred epsilon(t) conformation.

Synthesis and stereochemical characterization of diastereomeric nucleoside-phosphorothioselenoates by NMR methods

Synthesis and stereochemical characterization of enantiomerically pure nucleoside-phosphorothioselenoates are reported. The effects of solvent and temperature on the vicinal carbon-phosphorus couplings are described and the results are interpreted in terms of conformational changes influenced by stacking interactions between the bases and the phenyl rings.

Conformational properties of diastereomeric 5'-O-DMT-2'deoxythymidine 3'-O-(S-methyl-methanephosphonothiolate)s and -(se-methyl-methanephosphonoselenolate)s in solution as studied by NMR methods

Stereochemical characterization of diastereomerically pure 5'-O-DMT-2'deoxythymidine 3'-O-(S-methyl-methanephosphonothiolate)s and -(Se-methyl-methane-phosphono-selenolate)s by NMR methods are reported. (1)H-(1)H, (1)H-(31)P, and (13)C-(31)P coupling constants and nuclear overhauser enhancement (NOE) connectivities from transverse cross-relaxation experiments in rotating frame (T-ROESY) were measured to correlate the conformational properties of the isomers with the absolute configurations at the phosphorus obtained from X-ray studies of the relatives of S(p) configured isomers. Conformational differences between the stereoisomers were found to be restricted to the different orientation of the C3'-O3'-P bond. The NMR data reflected the preferred epsilon(-) conformation for the S(p) isomers, while in the R(p) isomers the conformational equilibrium was shifted toward the epsilon(t) domain. These results also indicated that for 5'-protected mononucleotides the absolute configuration at the phosphorus atom can be inferred from the NOE experiments and the trends observed in vicinal carbon-phosphorus coupling constants. Copyright 2000 Wiley-Liss, Inc.

Synthesis and NMR characterization of diastereomeric CPSMeG derivatives

Synthesis and stereochemical characterization of enantiomerically pure CPSMeG derivatives by NMR methods are reported. The effect of 5'-dimethoxytrityl on the conformational properties is described. It was found that in P-diastereomers the conformational differences about the C3'-O3' bond, as discernible from the delta J values, are enhanced by the presence of this protecting group.