以葡萄糖为极性头基的表面活性剂的合成及苯基酮在手性胶束中的不对称还原

Synthesis of Glucoside Surfactants and Asymmetric Reduction of Phenylalkylketones in Chiral Micelles

合成了三种长链烷基葡萄糖苷即1-O-十二烷基-β-D-葡萄糖(β-DG)、1-O-十二烷基-α-D-葡萄糖(α-DG)以及1-O-十二烷基-β-D-葡萄糖醛酸钠(Sβ-DGU)、三种化合物在水中均能形成胶束.在上述胶束中,用硼氢化钠对一系列苯基烷基甲酮进行了还原.在β-DG和α-DG胶束中所得到的还原产物苯基烷基甲醇均具有不同程度的光学活性.其中苯基乙基甲酮在β-DG胶束中的还原可达到98％e.e.的立体选择性.根据高疏水性受物不能被还原以及在阴离子胶束(Sβ-DGU)中受物难以被还原的实验结果.得出还原反应在靠近胶束极性头基层的内侧进行,并提出了二分子糖苷与BH_4^-形成的分子间负氢离子配合物是不对称还原得以产生的关键.上述推论被加入适量的非手性阳离子表面活性剂(CTAB)与β-DG所形成的混合胶束可充分抑制还原反应的立体选择性这一实验事实所证实.

Three glucosides with long alkyl group, dodecyl-β-D-glueopyranoside(β-DG); dodecyl-α-D-glucopyranoside(α-DG) and sodium 1-β-D-dodecyl glucopyranouranate(Sβ-DGU) were synthesized. All these glucosides form micelles in aqueous solution when the concentration is above the individual critical micellar concentration(cmc). Reduction of a variety of phenylalkylketones which were solubilized in the micelles formed from above glucoside were performed by sodium borohydride. In the micelles of β-DG or α-DG, a different level of optical yield were achieved, one of the most interesting example is for phenylethylketone in β-DG, the e. e. value is as high as 98%.It can be rationalized that the reduction takes place at interior side of polar layer of micelle by these experimental facts: no reduction for much hydrophobic substrates in any micelle and almost no reduction for all substrates in anionic micelle(β-DGU). An intermolecular negative hydrogen complex from BH_4 and two adjacent glucose moieties of glucoside surfactant was proposed in action of asymmetric reduction based on the result that the optical yield for β-DG micelle is completely inhibited by addition of a non-ligand surfactant, cetyl trimethylammonium bromide, CTAB.