Methyl 4-O-Acetyl-3-azido- and 3-Azido-4-O-methylsulfonyl-2,3,6,-trideoxyhex-5- enopyranosides in DFT-Level Conformational Studies

Geometry optimizations at the B3LYP level of density functional theory (DFT) are reported for methyl 4-O-acetyl-3-azido- and 3-azido-4-O-methylsulfonyl-2,3,6-trideoxy-alpha,beta-d-threo- and -beta-d-erythro-hex-5-enopyranosides. The most stable conformers for each compound are presented, along with the corresponding enthalpies and Gibbs free energies. The influence of the exocyclic double bond on the chair conformation is discussed. Conformations of the 1-OMe, 3-N3, and 4-OAc groups were examined, and delocalization in the OAc and N3 groups was demonstrated. The contributions of particular conformers to the total number of structures found for each hex-5-enopyranoside were calculated. The theoretical results are compared with assignments based on 1H NMR studies.

Synthesis and conformational studies on methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-hex-5-enopyranosides of the l series

Methyl 3-azido-2,3-dideoxy-alpha-D-xylo-, -alpha-D-lyxo-, and -beta-D-xylo-hexopyranosides were converted into 4-O-acetyl-3-azido-6-iodo-2,3,6-trideoxy analogues via 6-O-p-tolylsulfonyl compounds. The elimination of hydrogen iodide from 6-iodo glycosides yielded methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-beta-L-erythro-, -alpha-L-threo-, and -beta-L-threo-hex-5-enopyranosides. The configuration and conformation of all products are evaluated in depth on the basis of (1)H and (13)C NMR data. Factors determining conformational energy in 4-O-protected-3-azido-2,3,6,-trideoxy-hex-5-enopyranosides are discussed.