Cristina De Meo

Semi-orthogonality of O-pentenyl and S-ethyl glycosides: application for the oligosaccharide synthesis

Abstract Novel semi-orthogonal glycosylation strategy with the use of O -pentenyl and thioglycosides has been developed. According to this technique both armed and disarmed thioglycosides can be selectively activated with MeOTf in the presence of either armed or disarmed O -pentenyl glycosides. The applicability of this novel strategy for the synthesis of a trans – cis glycosylation pattern, not accessible via conventional armed–disarmed approach, has been demonstrated for the synthesis of a linear tetrasaccharide derivative.

How O-substitution of sialyl donors affects their stereoselectivity.

The profound effect of substituents at C-5 of glycosyl sialosides on their stereoselectivity is well-known although the exact nature of this effect is somewhat less understood. Presented herein is a comparative study of a range of novel sialyl donors with various O-substituents. It is demonstrated that O-substituents at C-4 and C-7 may also have a significant effect on the reactivity of sialyl donors and on the stereoselectivity of chemical sialylation.

Combined Effect of the Picoloyl Protecting Group and Triflic Acid in Sialylation

The stereoselective synthesis of sialosides is still one of the major challenges in carbohydrate chemistry. The synthesis and glycosidation of novel sialyl donors bearing a picoloyl substituent at C-4 are reported. High stereoselectivities and faster reactions were observed in the presence of an excess of triflic acid. The acid excess does not have the same effect on conventional sialyl donors, which suggests a possible synergistic effect of the picoloyl substituent and the triflic acid.

Synthesis and Elimination of C-3-Labeled Thiosialosides

The synthesis of C-3-labeled phenylthio sialic acid derivatives and an investigation of stereoselectivity in elimination reactions for the synthesis of 2,3-dehydro derivatives (glycals) is described. The experimental results are consistent with the existence of a conformational change and may be indicative of the intermediacy of an all-axial oxacarbenium ion.