Synthesis of pentaantennary N-glycans with bisecting GlcNAc and core fucose
Synthesis of pentaantennary N-glycans with bisecting GlcNAc and core fucose
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DOI：
10.1002/anie.200604788
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
Unverzagt, Carlo
中科院分区：
文献类型：
--
作者：
Eller, Steffen;Schuberth, Ralf;Unverzagt, Carlo
重组治疗性糖蛋白主要含有天冬酰胺连接的寡糖（N-聚糖），其通常对于糖蛋白的适当功能是必需的。天然糖蛋白中聚糖的异质性是糖生物学领域整个研究的一大障碍，[1]尽管最近在N-聚糖的化学合成方面取得了进展，[2-10]大多数用于生物学研究的N-聚糖仍然是从天然来源分离的。[11]我们已经为最丰富的复杂N-聚糖开发了模块化构建块，[12]在测试该模块化系统的偶然结果之后，允许合成具有最大数量的分支和核心取代的复杂N-聚糖（聚糖F;方案1）。之前，我们已经开发了用于合成具有多达四个天线的复杂N-聚糖的模块化构建块，[12]其含有二等分GlcNAc部分[4，13，14]或核心岩藻糖部分。[15]由于空间位阻，具有三个或四个天线的二等分N-聚糖特别难以获得。[4]受到最近改进的鼓舞[14]，我们研究了复合N-聚糖F（方案1）。在F的Manα1，6 Man β单元发现了特别高的取代模式，其中每个甘露糖含有总共四个糖苷配偶体。五触角N-聚糖存在于卵类粘蛋白、[16]鱼Hyosophorin、[17] CHO细胞和HepG 2细胞中。[19]首先，组装未取代的五触角N-聚糖以降低F的合成复杂性。四糖供体D的合成开始于苄基甘露糖苷（2）经由亚甲锡烷基缩醛的3-O-烯丙基化，得到3（方案2）。[20三醇3与供体1（6当量）的三倍糖基化得到四糖4（77%）。在4的脱烯丙基化之后，醇5的乙酰化需要催化量的DMAP。在催化氢化6以除去苄基后，半缩醛转化为亚氨酸酯D，并与六糖12偶联，在优化后以65%的产率得到十糖13（方案3）。因此，支链三糖B [12]与核心三糖A偶联（方案4）。[15]将所得六糖（80%）乙酰化，并裂解亚苄基缩醛（75%，经2步）。在14的选择性氯乙酰化之后，六糖15与硫代糖苷C偶联[4]，得到平分的七糖16。脱氯乙酰化产生受体17，其与二糖18偶联（77%）。将九糖19脱保护并岩藻糖基化，得到三触角十糖21，产率为93%。
Recombinant therapeutic glycoproteins contain mainly asparagine-linked oligosaccharides (N-glycans), which are often essential for the proper function of the glycoprotein. The heterogeneity of the glycans in natural glycoproteins is a large obstacle for the entire research in the field of glycobiology,[1] and despite recent advances in chemical synthesis of N-glycans,[2–10] the majority of N-glycans for biological studies are still isolated from natural sources.[11] We have developed modular building blocks for the most abundant complex N-glycans,[12] which after fortuitous results from the test of this modular system allowed the synthesis of complex N-glycans with the maximum number of branches and core substitutions (glycan F; Scheme 1). Previously we have developed modular building blocks for the synthesis of complex N-glycans with up to four antennae,[12] which contained a bisecting GlcNAc moiety [4, 13, 14] or a core fucose moiety.[15] As a result of the steric hindrance, bisected N-glycans with three or four antennae are especially difficult to obtain.[4] Encouraged by recent improvements [14] we investigated the complex N-glycan F (Scheme 1). A particularly high substitution pattern is found at the Manα1, 6Manβ unit of F where each mannose contains a total of four glycosidic partners. Pentaantennary N-glycans are found in ovomucoid,[16] fish hyosophorin,[17] CHO cells,[18] and HepG2 cells.[19] First, unsubstituted pentaantennary N-glycans were assembled to reduce the synthetic complexity of F. The synthesis of tetrasaccharide donor D began with the 3-O-allylation of benzylmannoside (2) via a stannylene acetal to give 3 (Scheme 2).[20, 21] Threefold glycosylation of triol 3 with donor 1 (6 equiv) gave the tetrasaccharide 4 (77%). After deallylation of 4, the acetylation of alcohol 5 required catalytic amounts of DMAP. After catalytic hydrogenation of 6 to remove the benzyl group, the hemiacetal was converted into imidate D and coupled with the hexasaccharide 12 to give the decasaccharide 13 in 65% yield after optimization (Scheme 3).The high reactivity of donor D prompted us to incorporate a bisecting GlcNAc moiety and a core fucose residue. Thus, the branched trisaccharide B [12] was coupled to the core trisaccharide A (Scheme 4).[15] The resulting hexasaccharide (80%) was acetylated and the benzylidene acetal was cleaved (75% over 2 steps). After the selective chloroacetylation of 14, the hexasaccharide 15 was coupled with thioglycoside C [4] to give the bisected heptasaccharide 16. Dechloroacetylation yielded the acceptor 17, which was coupled with the disaccharide 18 (77%). The nonasaccharide 19 was deprotected and fucosylated to give the triantennary decasaccharide 21 in 93% yield.