Comparative studies on the O-sialylation with four different α/β-oriented (N-acetyl)-5-N,4-O-carbonyl-protected p-toluenethiosialosides as donors
作者:Xiao-tai Zhang、Zhen-yuan Gu、Guo-wen Xing
DOI:10.1016/j.carres.2014.02.006
日期:2014.3
Four types of 5-N,4-O-carbonyl-protected p-toluenethiosialosides were synthesized and their couplings with different acceptors were thoroughly investigated. The results indicate that the sialyl donor structure, the amount of glycosyl acceptor, and the detailed promotion conditions have great influence on the sialylation stereoselectivties and product yields. Under the (p-Tol)(2)SO/Tf2O activation conditions, the glycosylations with simple alcohols provided declined alpha-selectivities and higher yields with increasing the amounts of acceptors from 1.1 equiv to 2.0 equiv. However, the outcome of same sialylation was independent of the relative amounts of sugar alcohol acceptors. With NIS/TfOH as promoter, the alpha-selectivities of the sialylations were significantly improved compared with the cases activated by (p-Tol)(2)SO/Tf2O. In general, the difference in configuration of N-acetylated sialyl donors (D2 and D4) has little effect on the sialylation yield and stereoselectivity. In contrast, the N-deacetylated alpha/beta sialyl donors (D1 and D3) show complex sialylation profiles with different acceptors. (C) 2014 Elsevier Ltd. All rights reserved.