Diblock oligosaccharides based on renewable resources allow for a range of new but, so far, little explored biomaterials. Coupling of blocks through their reducing ends ensures retention of many of their intrinsic properties that otherwise are perturbed in classical lateral modifications. Chitin is an abundant, biodegradable, bioactive, and self-assembling polysaccharide. However, most coupling protocols relevant for chitin blocks have shortcomings. Here we exploit the highly reactive 2,5-anhydro-d-mannose residue at the reducing end of chitin oligomers obtained by nitrous acid depolymerization. Subsequent activation by dihydrazides or dioxyamines provides precursors for chitin-based diblock oligosaccharides. These reactions are much faster than for other carbohydrates, and only acyclic imines (hydrazones or oximes) are formed (no cyclic N-glycosides). α-Picoline borane and cyanoborohydride are effective reductants of imines, but in contrast to most other carbohydrates, they are not selective for the imines in the present case. This could be circumvented by a simple two-step procedure. Attachment of a second block to hydrazide- or aminooxy-functionalized chitin oligomers turned out to be even faster than the attachment of the first block. The study provides simple protocols for the preparation of chitin-b-chitin and chitin-b-dextran diblock oligosaccharides without involving protection/deprotection strategies.

中文翻译：

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被二氧胺或二酰肼活化为二嵌段低聚糖的前体的2,5-脱水-甘露糖末端官能化几丁质低聚物。

基于可再生资源的二嵌段低聚糖可用于多种新型生物材料，但迄今为止，探索的生物材料很少。块体通过其还原端进行耦合可确保保留其许多固有特性，这些特性否则会在经典的横向修改中受到干扰。几丁质是一种丰富，可生物降解，具有生物活性的自组装多糖。但是，大多数与几丁质嵌段有关的偶联方案都有缺点。这里，我们利用高反应性的2,5-脱水- d亚硝酸解聚得到的几丁质低聚物还原端的-甘露糖残基。随后通过二酰肼或二氧胺的活化提供了基于甲壳质的二嵌段低聚糖的前体。这些反应比其他碳水化合物要快得多，并且仅形成无环亚胺（hydr或肟）（无环氮-糖苷）。α-二十二烷基硼烷和氰基硼氢化物是亚胺的有效还原剂，但与大多数其他碳水化合物相比，在当前情况下它们对亚胺没有选择性。这可以通过简单的两步过程来避免。结果表明，第二个嵌段与酰肼或氨基氧基官能化的几丁质低聚物的连接比第一个嵌段的连接甚至更快。该研究提供了几丁质-b-甲壳质和几丁质-b-右旋糖酐二嵌段寡糖的简单制备方法，而无需涉及保护/去保护策略。