Rademann J, Schmidt R R
Fakultät für Chemie, Universität Konstanz, Germany.
Carbohydr Res. 1995 Apr 19;269(2):217-25. doi: 10.1016/0008-6215(94)00364-l.
A hexapeptide containing a beta-D-Gal p-(1-->3)-alpha-D-Gal pNAc-(1-->O)-L-threonine unit was synthesized using glycosylated pentafluorophenyl esters in an Fmoc-based strategy. In all of the glycosylation reactions, trichloroacetimidates were successfully employed. The disaccharide moiety was prepared from tetra-O-acetyl-alpha-D-galactopyranosyl trichloroacetimidate and tert-butyldimethylsilyl 2-azido-6-O-benzoyl-2-deoxy-beta-E-galactopyranoside with boron trifluoride etherate as a catalyst. The glycosylated active esters were obtained in the reaction of alpha and beta 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl-(1-->3)-4-O-acetyl-2-azid o-6- O-benzoyl-2-deoxy-D-galactopyranosyl trichloroacetimidates with Fmoc-protected pentafluorophenyl esters of L-serine and L-threonine in the presence of trimethylsilyl trifluoromethanesulfonate as Lewis acid. The glycosylated pentafluorophenyl ester of L-threonine was transformed into glycopeptides via a solid-phase synthesis. Azide reduction and N-acetylation were performed on the solid phase with a thioacetic acid-pyridine mixture. The glycopeptide was then cleaved from the resin with strong acid, also removing the acid-labile protecting groups of the peptide chain. Finally, the acyl groups used for sugar protection were cleaved with sodium methoxide, affording the completely deprotected N-acetyl-L-leucyl-L-glutamyl-O-[beta-D-galactopyranosyl-(1-->3)-2- acetamido-2-deoxy-alpha-D-galactopyranosyl]-L-threonyl-L-seryl-L-threony l- glycinamide (1) in high purity.
采用基于Fmoc的策略，使用糖基化五氟苯基酯合成了一种含有β-D-半乳糖p-(1→3)-α-D-半乳糖胺基-(1→O)-L-苏氨酸单元的六肽。在所有糖基化反应中，均成功使用了三氯乙酰亚胺酯。二糖部分由四-O-乙酰基-α-D-吡喃半乳糖基三氯乙酰亚胺酯和叔丁基二甲基甲硅烷基2-叠氮基-6-O-苯甲酰基-2-脱氧-β-E-吡喃半乳糖苷在三氟化硼乙醚作为催化剂的条件下制备。α和β 2,3,4,6-四-O-乙酰基-β-D-吡喃半乳糖基-(1→3)-4-O-乙酰基-2-叠氮基-6-O-苯甲酰基-2-脱氧-D-吡喃半乳糖基三氯乙酰亚胺酯与Fmoc保护的L-丝氨酸和L-苏氨酸的五氟苯基酯在三甲基甲硅烷基三氟甲磺酸酯作为路易斯酸的存在下反应，得到糖基化活性酯。L-苏氨酸的糖基化五氟苯基酯通过固相合成转化为糖肽。在固相上用硫代乙酸-吡啶混合物进行叠氮还原和N-乙酰化。然后用强酸将糖肽从树脂上裂解下来，同时除去肽链上对酸不稳定的保护基团。最后，用甲醇钠裂解用于糖保护的酰基，得到高纯度的完全脱保护的N-乙酰-L-亮氨酰-L-谷氨酰-O-[β-D-吡喃半乳糖基-(1→3)-2-乙酰氨基-2-脱氧-α-D-吡喃半乳糖基]-L-苏氨酰-L-丝氨酰-L-苏氨酰-甘氨酰胺(1)。
