Exploring Photoredox Catalytic Reactions as an Entry to Glycosyl-α-amino Acids

Abstract

The synthesis of glycosyl-α-amino acids presents a significant challenge due to the need for precise glycosidic linkages connecting carbohydrate moieties to amino acids while maintaining stereo- and regiochemical fidelity. Classical methods relying on ionic intermediates (2e^–) often involve intricate synthetic procedures, particularly when dealing with 2-N-acetamido-2-deoxyglycosides linked to α-amino acids─a crucial class of glycoconjugates that play important biological roles. Considering the growing prominence of photocatalysis, this study explores various photoredox catalytic approaches to achieving glycosylation reactions. Our focus lies on the notoriously difficult case of 2-N-acetamido-2-deoxyglycosyl-α-amino acids, which could be obtained efficiently by two methodologies that involved, on the one hand, photoredox Giese reactions using a chiral dehydroalanine (Dha) as an electron density-deficient alkene in these radical 1,4-additions and, on the other hand, photoredox glycosylations using selenoglycosides as glycosyl donors and hydroxyl groups of protected amino acids as acceptors.