An expeditious and efficient synthesis of β- d-galactopyranosyl-(1→3)- d- N-acetylglucosamine (lacto- N-biose) using a glycosynthase from Thermus thermophilus as a catalyst

Abstract

Mutant glycosynthases or transglycosidases obtained from a Thermus thermophilus β- d-glycosidase (TtbGly) efficiently catalyzed the synthesis of β-(1→3)-disaccharides. Unfortunately, this regioselectivity was changed to the β-(1→4) one when N-acetylglucosamine derivatives were used as acceptors, thus precluding the possibility of synthesizing d-Gal p-β-(1→3)- d-Glc pNAc (lacto- N-biose) or d-Glc p-β-(1→3)- d-Glc pNAc, which are useful synthons for the synthesis of antigen determinants. In contrast, we show in this work that, in the presence of phenyl 2-amino-1-thio-β- d-glucopyranoside, the ‘normal’ β-(1→3) regioselectivity of E338G TtbGly glycosynthase takes place. Thus, transglycosylations using α-galactosyl or α-glucosyl fluorides gave the corresponding phenyl β- d-glycopyranosyl-(1→3)-2-amino-2-deoxy-1-thio-β- d-glucopyranosides in high yields (88–97%). Subsequent selective N-acylation followed by NBS/water deprotection of the thiophenyl group afforded lacto- N-biose in high overall yields.