title: Comparative studies on the O-sialylation with four different α/β-oriented (N-acetyl)-5-N,4-O-carbonyl-protected p-toluenethiosialosides as donors.
abstract: 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)2SO/Tf2O activation conditions, the glycosylations with simple alcohols provided declined α-selectivities and higher yields with increasing the amounts of acceptors from 1.1 equiv to 2.0equiv. However, the outcome of same sialylation was independent of the relative amounts of sugar alcohol acceptors. With NIS/TfOH as promoter, the α-selectivities of the sialylations were significantly improved compared with the cases activated by (p-Tol)2SO/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 α/β sialyl donors (D1 and D3) show complex sialylation profiles with different acceptors.
authors.affiliation: Department of Chemistry, Beijing Normal University, Beijing 100875, China.
authors.forename: Xiao-tai
authors.initials: XT
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Beijing Normal University, Beijing 100875, China.
authors.forename: Zhen-yuan
authors.initials: ZY
authors.lastname: Gu
authors.affiliation: Department of Chemistry, Beijing Normal University, Beijing 100875, China. Electronic address: gwxing@bnu.edu.cn.
authors.forename: Guo-wen
authors.initials: GW
authors.lastname: Xing
mesh_terms: D000107:Acetylation; D006031:Glycosylation; D015394:Molecular Structure; D012794:Sialic Acids / Q000737:chemistry*; D013237:Stereoisomerism; D013402:Sugar Alcohols / Q000737:chemistry; D014050:Toluene / Q000031:analogs & derivatives / Q000737:chemistry*
chemical_list: D012794:Sialic Acids; D013402:Sugar Alcohols; D014050:Toluene
keywords: Promoter; Sialic acid; Sialylation; Stereoselectivity; p-Toluenethiosialoside