Versatile solid-phase thiolytic reduction of azido and N-Dts groups in the synthesis of haemoglobin (67–76) O-glycopeptides and photoaffinity labelled analogues to study glycan T-cell specificity
作者:Ernst Meinjohanns、Morten Meldal、Teis Jensen、Ole Werdelin、Luisa Galli-Stampino、Søren Mouritsen、Klaus Bock
DOI:10.1039/a606725e
日期:——
A series of O-glycosylated peptides and
photoaffinity labelled glycopeptide analogues of the mouse
haemoglobin-derived decapeptide Hb (67â76), VITAFNEGLK, which
binds well to the MHC class II Ek molecule and is
non-immunogenic in CBA/J mice, was synthesized by multiple-column
peptide synthesis employing the glycosylated building blocks 1â4
and 7â21. The non-immunogenic peptide VITAFNEGLK was converted
into an immunogen by introducing different tumour-associated
carbohydrate moieties
[β-D-GlcNAc-O
-Ser/Thr,
α-D-GalNAc-O-Ser/Thr
(TN-antigen) core 1 (T-antigen), core 2, core 3 and core
4] to the central position Asn-72 in the decapeptide.
Previous studies suggest that T cells may be capable of recognizing
epitopes which are partially defined by glycans and may be in direct
contact with the T-cell receptor. In order to study the specificity of
glycan interactions with the T-cell receptor a series of corresponding
glycopeptides labelled with 2-azidobenzamide on the carbohydrate amino
function was synthesized. The glycan structure was varied with respect
to O-GlcNAc, T and TN-antigen moieties and
anomeric configuration. Throughout, efficient reduction of the
N-dithiasuccinyl- and azido-functionality-containing
building blocks 1, 2, 7, 8, 11, 12, 13, 16, 18 and 20 could be achieved
either (i) in solution by utilizing simultaneous in
situ reduction with Zn in THFâHOAcâAc2O
or (ii) on solid-phase upon treatment with diisopropylethylamine and an
excess of dithiothreitol or
α-mercapto-N-methylacetamide. N-Acetylation of
the resin-bound glycopeptides furnished the
O-glycopeptides 24, 25 and 31â36. No further
modification of the carbohydrate moiety on the solid phase was required
when utilizing the N-acetylated building blocks 3, 4, 9, 10, 14, 15, 17,
19 and 21. In addition, comparative studies with solid-phase reduction
were conducted for the syntheses of the O-linked glycopeptides 24, 25
and 31â36 by employing any of the building blocks 1â4 and
7â21. The photoaffinity labelled glycopeptides 39â45 were
synthesized by employing building blocks 1, 2, 7, 8 and 11â13 by
reduction of azido or N-Dts functionalities by
thiolysis with dithiothreitol and subsequent coupling of the activated
photoaffinity label 38 to the glycanamino group of the resin-bound
glycopeptides. The synthesized mucin O-glycopeptides
24, 25 and 31â36 and the photoaffinity labelled analogues
39â45 were fully characterized by 1D and 2D 1H NMR
spectroscopy and by electrospray mass spectrometry.
利用糖基化结构单元 1â4 和 7â21 通过多柱肽合成法合成了一系列 O-糖基化肽和光亲和标记的小鼠血红蛋白衍生十肽 Hb(67â76)的糖肽类似物 VITAFNEGLK,它能很好地与 MHC II 类 Ek 分子结合,并且对 CBA/J 小鼠无免疫原性。通过在十肽的中心位置 Asn-72 引入不同的肿瘤相关碳水化合物分子 [δ-D-GlcNAc-O-Ser/Thr、δ-D-GalNAc-O-Ser/Thr(TN 抗原)核心 1(T 抗原)、核心 2、核心 3 和核心 4],将非免疫原性肽 VITAFNEGLK 转化为免疫原。
以往的研究表明,T 细胞可能能够识别部分由聚糖定义的表位,并可能与 T 细胞受体直接接触。为了研究聚糖与 T 细胞受体相互作用的特异性,我们合成了一系列在碳水化合物氨基功能上用 2- 叠氮苯甲酰胺标记的相应聚糖肽。聚糖结构随 O-GlcNAc、T 和 TN 抗原分子以及异构体构型的不同而变化。自始至终,含 N-二硫代丁二酰基和叠氮官能团的结构单元 1、2、7、8、11、12、13、16、18 和 20 都可以通过以下两种方法实现高效还原:(i) 在溶液中用 Zn 在 THFâHOAcâAc2O 中同时原位还原;或 (ii) 在固相上用二异丙基乙胺和过量的二硫苏糖醇或δ-巯基-N-甲基乙酰胺处理。对树脂结合的糖肽进行 N-乙酰化,可得到 O-糖肽 24、25 和 31â36。在使用 N-乙酰化结构单元 3、4、9、10、14、15、17、19 和 21 时,不需要在固相上进一步修饰碳水化合物分子。此外,在合成 O-连接糖肽 24、25 和 31â36 时,还进行了固相还原比较研究,采用的是 1â4 和 7â21 中的任何一种构建模块。光亲和标记的糖肽 39â45 是通过使用构建模块 1、2、7、8 和 11â13 合成的,方法是用二硫苏糖醇进行硫醇分解还原叠氮或 N-Dts 官能,然后将活化的光亲和标记 38 与树脂结合的糖肽的甘氨酸基偶联。通过一维和二维 1H NMR 光谱以及电喷雾质谱法,对合成的粘蛋白 O 型糖肽 24、25 和 31â36 以及光亲和标记的类似物 39â45 进行了全面鉴定。