An efficient synthesis of L-idose and L-iduronic acid thioglycosides and their use for the synthesis of heparin oligosaccharides.

Efficient preparations of thioglycoside derivatives of L-idose and L-iduronic acid are described. The method avoids the tedious chromatographic separations of furanose and pyranose anomeric mixtures, and affords the thioglycosides in a stereoselective manner. The L-idose and L-iduronic acid thioglycosides having combinations of different protecting groups proved to be efficient glycosyl donors in the synthesis of heparin disaccharides.

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.

NMR study of some diastereomeric nucleoside-3'-thiophosphate derivatives in solution.

The conformational properties of diastereomeric P-modified nucleotides are reported as reflected by different NMR parameters. Some conformational trends can be rationalized by consideration of the (3) J(C4',P)()and (3) J(C2',P) coupling values of the isomers and the nature of the substituent on the phosphorus. Configurational assessment of the phosphorus is inferred from NOE experiments. The effects of temperature, solvent and size of substituents are presented.

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 of vinca alkaloids and related compounds. 100. Stereoselective oxidation reactions of compounds with the aspidospermane and quebrachamine ring system. First synthesis of some alkaloids containing the epoxy ring.

The first syntheses of the alkaloids (-)-mehranine (3), (+)-voaphylline/conoflorine (4), (+)-N(a)-methylvoaphylline/hecubine (5), and (-)-lochnericine (2) were achieved by stereoselective epoxidation starting from (-)-tabersonine (1), through intermediates with the aspidospermane and quebrachamine skeleton.