The trisaccharide–serine conjugate [Gal(β1-3)Gal(β1-4)Xyl(β)-Ser], constituting the linkage region between the glycosaminoglycan and protein in proteoglycan, was synthesized by using enzymatic transglycosylation with a β-d-galactosidase as a key reaction. The yields of transglycosylation were much improved by using galactosyl fluoride as a donor in comparison with those obtained by a conventional p-nitrophenyl (PNP) galactoside. After enzymatic synthesis of Gal(β1-3)Gal(β1-4)Xyl(β)–PNP, cleavage of the PNP group of the fully acetylated trisaccharide, chemical coupling with serine, and final deprotection afforded Gal(β1-3)Gal(β1-4)Xyl(β)–Ser.
三糖-
丝氨酸偶联物[Gal(β1-3)Gal(β1-4)Xyl(β)-Ser],构成蛋白聚糖中糖胺聚糖与蛋白质之间的连接区域,是通过使用β-
D-半乳糖苷酶作为关键反应的酶促转糖苷作用合成的。与传统的对
硝基苯(
PNP)半
乳糖苷作为供体相比,使用半
乳糖氟化物作为供体显著提高了转糖苷作用的产量。在酶促合成了Gal(β1-3)Gal(β1-4)Xyl(β)-
PNP后,完全乙酰化的三糖的
PNP基团的裂解,与
丝氨酸的
化学偶联,以及最终的去保护作用,得到了Gal(β1-3)Gal(β1-4)Xyl(β)-Ser。