Base- and Radical-Mediated Regio- and Stereoselective Additions of Thiols, Thio-Sugars, and Thiol-Containing Peptides to Trisubstituted Activated exo -Glycals
Abstract
A study was performed for the coupling of thiols, thio-sugars, and thiol-containing amino acids and peptides with trisubstituted activated anomeric sugar olefins under basic and radical conditions. The hydrothiolation reaction took place in a regio- and stereospecific manner and occurred at the anomeric center and mainly from an approach to the less crowded face, that is, opposite to the O-4 protecting group. Furano- and pyranoglycosylidenes were valuable substrates for the base-mediated coupling with aromatic and primary thiols, which included 6-thio-sugars, cysteine derivatives, and glutathione. The success of the radical-mediated method depended on the thiol partners as well as the nature of the sugar olefins. Neither of the conditions required the protection of the sugar or the cysteine derivatives.