Synthesis of Lacto-N-neohexaose and Lacto-N-neooctaose Using the Dimethylmaleoyl Moiety as an Amino Protective Group

The N-DMM-Protected lactosamine derivative 2 was readily transformed into the corresponding glycosyl donor 4 and into acceptor 5. A TMSOTf-catalyzed glycosidation afforded the derived tetrasaccharide 6 which led to glycosyl donor 9. Reaction of 9 with lactose derivative 10 as acceptor gave the desired hexasaccharide 11. Cleavage of all protective groups and N-acetylation afforded the target molecule 1b (lacto-N-neohexaose). Glycosylation of acceptor 10 with donor 4 furnished tetrasaccharide 16 which, employing standard procedures, gave acceptor 18. Glycosylation of 18 with donor 9 furnished, under standard conditions, octasaccharide 19. Cleavage of all protective groups and N-acetylation afforded the target molecule 1c (lacto-N-neooctaose). Both 1b and 1c were obtained in good overall yields.