2-O-N-Benzylcarbamoyl as a Protecting Group To Promote β-Selective Glycosylation and Its Applications in the Stereoselective Synthesis of Oligosaccharides

Abstract

This study examines the utility of the N-benzylcarbamoyl (BnCar) protecting group in glycosylation reactions of the parent O-2 protected carbohydrate donor. It was found that the BnCar group imparted exclusively β-selectivity with primary and secondary alcohols. A mechanistic study revealed the activated intermediate to be the glycosyl triflate in a skew conformation, which results in β-selective glycosylation via an SN2-like pathway. The BnCar group can be readily cleaved using tetrabutylammonium nitrite, without affecting ester and ether protecting groups. Taken together, these results show BnCar to be useful for the synthesis of complex oligosaccharides, an undertaking that requires delicate chemical differentiation of various protecting groups.

Biological and Pharmacological Effects of Synthetic Saponins

“…The synthetic methods of saponins have been well reviewed, providing complete information on the organic synthesis to perform SAR optimization [6,7]. Based on the research experiences on carbohydrate [8,9] and medicinal [10][11][12][13][14][15][16][17][18][19][20][21][22] chemistry in our lab, we summarize the biological effects and preliminary SAR results of synthetic saponins over the last five years to serve as a bridge between chemistry and biology, providing an insight for further structure optimization and mechanism studies, finally facilitating the development of saponin-based bioactive compounds.…”

Advances in Protecting Groups for Oligosaccharide Synthesis

“…N-benzylcarbamoyl (BnCar) protecting group has also provedt og ive exclusive b-selectivity when installed at the 2positiono ft he donor substrate in glycosylation. [31] The reason behind its exclusive stereoselectivity is the formationo fa ctivated intermediate which is glycosyl triflate in the skew conformation. For the protection of BnCar group into the sugar alco-hol, benzyli socyanate was treated with the sugar substrate in the presence of copper(I) iodide while the deprotection was conducted with tetra butyl ammonium nitrite withouta ffecting the ester and ether protecting groups.…”

“…N ‐benzylcarbamoyl (BnCar) protecting group has also proved to give exclusive β‐selectivity when installed at the 2‐position of the donor substrate in glycosylation . The reason behind its exclusive stereoselectivity is the formation of activated intermediate which is glycosyl triflate in the skew conformation.…”