Porwal Mayuri K, Reddi Yernaidu, Saxon Derek J, Cramer Christopher J, Ellison Christopher J, Reineke Theresa M
Department of Chemical Engineering and Materials Science, University of Minnesota Minneapolis Minnesota 55455 USA
Department of Chemistry, University of Minnesota Minneapolis Minnesota 55455 USA
Chem Sci. 2022 Mar 17;13(16):4512-4522. doi: 10.1039/d2sc00146b. eCollection 2022 Apr 20.
We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality, which can be synthetically modified to install a variety of pendant groups for tailored properties. We have employed biocompatible and recyclable metal triflate catalysts - scandium and bismuth triflate - for green cROP of levoglucosan derivatives, even at very low catalyst loadings of 0.5 mol%. Combined experimental and computational studies provided key kinetic, thermodynamic, and mechanistic insights into the cROP of these derivatives with metal triflates. Computational studies reveal that ring-opening of levoglucosan derivatives is preferred at the 1,6 anhydro linkage and cROP proceeds in a regio- and stereo-specific manner to form 1,6-α glycosidic linkages. DFT calculations also show that biocompatible metal triflates efficiently coordinate with levoglucosan derivatives as compared to the highly toxic PF used previously. Post-polymerization modification of levoglucosan-based polysaccharides is readily performed UV-initiated thiol-ene click reactions. The reported levoglucosan based polymers exhibit good thermal stability ( > 250 °C) and a wide glass transition temperature ( ) window (<-150 °C to 32 °C) that is accessible with thioglycerol and lauryl mercaptan pendant groups. This work demonstrates the utility of levoglucosan as a renewably-derived scaffold, enabling facile access to tailored polysaccharides that could be important in many applications ranging from sustainable materials to biologically active polymers.
我们报道了通过生物质衍生的左旋葡聚糖阳离子开环聚合（cROP）实现1,6-α连接的功能性立构规整多糖的简便合成与表征。左旋葡聚糖是一种具有丰富羟基官能团的双环缩醛，可通过合成修饰来引入各种侧基以实现定制性能。我们采用了生物相容性且可回收的金属三氟甲磺酸盐催化剂——三氟甲磺酸钪和三氟甲磺酸铋——用于左旋葡聚糖衍生物的绿色cROP，即使在低至0.5 mol%的催化剂负载量下也能实现。结合实验和计算研究，为这些衍生物与金属三氟甲磺酸盐的cROP提供了关键的动力学、热力学和机理见解。计算研究表明，左旋葡聚糖衍生物在1,6-脱水键处开环更有利，且cROP以区域和立体特异性方式进行，形成1,6-α糖苷键。密度泛函理论（DFT）计算还表明，与先前使用的剧毒PF相比，生物相容性金属三氟甲磺酸盐能更有效地与左旋葡聚糖衍生物配位。基于左旋葡聚糖的多糖的后聚合修饰可通过紫外光引发的硫醇-烯点击反应轻松实现。所报道的基于左旋葡聚糖的聚合物表现出良好的热稳定性（>250°C）和较宽的玻璃化转变温度范围（<-150°C至32°C），通过硫代甘油和月桂基硫醇侧基可实现该温度范围。这项工作证明了左旋葡聚糖作为可再生来源支架的实用性，能够轻松获得定制的多糖，这在从可持续材料到生物活性聚合物等许多应用中可能都很重要。
