O-Glycosylation of serine derivatives carried out with N-urethane protected glucosamine yields O-glycopeptides which are regio-and stereoselectively galactosylated with the aid of ~-1,4-galactosyltranaferase (EC 2.4.1.22 ).
Chemical syntheses of glycopeptides require a complex methodology of multi-step procedures, in order to protect and selectively deproteet the various functionalities. Especially, the regio-and stereoselective formation of the intersaccharidie bond poses great synthetic demands. In this context the use of giycosyltransferases promises a number of advantages. Characteristically, these enzymes catalyze reactions in a mild and stereoselective way and accept a broad range of substrates. Among these biocatalysts, the commercially available [3-1,4-galactosyltransferase (EC 2.4.1.22) is most thoroughly investigated. Its preparative value was successfully proven by galactosylations of oligosaccharides 1) and N-giycopeptides.2, 3) We here report on the preparative enzymatic galactosylation of O-glycopeptides derived from glucosarnine. Glycoproteins which contain this linkage region widely occur in subeellular fractions of vertebrates. 4) For this reason, the chemical synthesis of the required substrates, i.e. 13-N-aeetylglucosamine serine and threonine conjugates, was another matter of interest.