Efficient O - and S -glycosylation with ortho -2,2-dimethoxycarbonylcyclopropylbenzyl thioglycoside donors by catalytic strain-release.

We herein present a strain-release glycosylation method employing a rationally designed ortho -2,2-dimethoxycarbonylcyclopropylbenzyl (CCPB) thioglycoside donor. The donor is activated through the nucleophilic ring-opening of a remotely activable donor-acceptor cyclopropane (DAC) catalyzed by mild Sc(OTf) 3 . Our new glycosylation method efficiently synthesizes O -, N -, and S -glycosides, providing facile chemical access to the challenging S -glycosides. Because the activation conditions of conventional glycosyl donors and our CCPB thioglycoside are orthogonal, our novel donor is amenable to controlled one-pot glycosylation reactions with conventional donors for expeditious access to complex glycans. The strain-release glycosylation is applied to the assembly of a tetrasaccharide of O -polysaccharide of Escherichia coli O-33 in one pot and the synthesis of a 1,1'-S-linked glycoside oral galectin-3 (Gal-3) inhibitor, TD139, to demonstrate the versatility and effectiveness of the novel method for constructing both O - and S -glycosides.