| Synthetic methods have been used to assemble carabasugar analogues of methyl alpha-D-arabinofuranoside and methyl beta-D-arabinofuranoside. The synthetic route developed involves the conversion of D-mannose into a protected diene, which is cyclized via olefin metathesis. The resulting cyclopentene was used for the synthesis of both carbasugar monosaccharide analogues as well as the intermediates for the assembly of the disaccharide carbasugar analogues. Through the use of NMR spectroscopy and ab initio molecular orbital and density functional computational methods, we have probed the conformation of these molecules and showed that there are conformational differences between these carbasugars and their glycoside parents.; To gain a better understanding of computational studies on strongly hydrogen bonded systems, we studied all 126 possible conformations of 1,2,3-propanetriol (glycerol) by ab initio molecular orbital and density functional theory calculations at multiple levels of theory and basis set in the gas and aqueous phase. The efficiency of basis set and level of theory in dealing with the issue of intramolecular hydrogen bonding and reproducing the correct energetic and geometrical trends was determined.; We have shown that 2,3-anhydrofuranose thioglycosides and glycosyl sulfoxides, glycosylate alcohols with an exceptionally high degree of stereocontrol as a new method for glycosidic bond formation. The predominant or exclusive product of reactions with these glycosylating agent is the one in which the newly formed glycosidic bond is cis to the epoxide moiety. We also investigated the effect of stereochemistry at the anomeric center in 2,3-anhydro- O-furanosides on the magnitude of the one-bond coupling constant between C1 and H1.; We have also shown that subsequent nucleophilic opening of the epoxide moiety in the 2,3-anhydro-glycosides proceeds under basic conditions to give products in high yield and with good to excellent regioselectivity. The major ring-opened products possess the arabino stereochemistry. In the epoxide ring-opening reactions of glycosides with the 2,3-anhydro-beta- D-lyxo stereochemistry, the addition of (-)-sparteine to the reaction mixture dramatically enhanced the regioselectivity in favor of the arabino product. We have demonstrated the utility of this methodology through the synthesis of an arabinofuranosyl hexasaccharide, which is a key structural motif in two mycobacterial cell wall polysaccharides. (Abstract shortened by UMI.)... |
