Enzymic synthesis of lacto-N-triose II and its positional analogues

摘要

N-acetylhexosaminidase fromNocardia orientaliscatalysed the synthesis of lacto-N-triose II glycoside (β-d-GlcNAc-(1-3)-β-d-Gal-(1-4)-β-d-Glc-OMe,3) with its isomers β-d-GlcNAc-(1-6)-β-d-Gal-(1-4)-β-d-Glc-OMe (4) and β-d-Gal-(1-4)-β-d-GlcNAc-(1-6)-β-d-Glc-OMe (5) throughN-acetylglucosaminyl transfer fromN,N′-diacetylchitobiose (GlcNAc2) to methyl β-lactoside. The enzyme formed the mixture of trisac-charides3, 4and5in 17 overall yield based on GlcNAc2, in a ratio of 20:21:59. Withp-nitrophenyl β-lactoside as an acceptor, the enzyme also producedp-nitrophenyl β-lacto-N-trioside II (β-d-GlcNAc-(1-3)-β-d-Gal-(1-4)-β-d-Glc-OC6H4NO2-p,6) with its isomers β-d-GlcNAc-(1-6)-β-d-Gal-(1-4)-β-d-Glc-OC6H4NO2-p(7) and β-d-Gal-(1-4)-β-d-GlcNAc-(1-6)-β-d-Glc-OC6H4NO2-p(8). In this case, when an inclusion complex ofp-nitrophenyl lactoside acceptor with β-cyclodextrin was used, the regioselectivity of glycosidase-catalysed formation of trisaccharide glycoside was substantially changed. It resulted not only in a significant increase of the overall yield of transfer products, but also in the proportion o