1-Methyl 1′-cyclopropylmethyl (MCPM) as an anomeric protecting group

A pragmatic approach for preparing glycoconjugates of complex oligosaccharides is to prepare the oligosaccharide as a building block with most of its protecting groups exchanged to protecting groups whose cleavage and other manipulations are highly compatible with the functional groups of complex aglycones. For such an approach the reducing end sugar of the building bloc must be protected with a cleavable protecting group during the oligosaccharide synthesis. We demonstrate that the acid labile 1-methyl 1′-cyclopropylmethyl (MCPM) can be effectively used for this purpose. A trisaccharide glycolipid and a disaccharide glycoamino acid are prepared. The absolute chirality of the MCPM in one key acceptor is determined by a combination of NMR NOE measurements, DFT molecular modeling and Noyori catalyst catalyzed asymmetric reduction.