First Application of Biopolymers for Chiral Reaction Field of Asymmetric Photoreactions

在这项研究中，作者提出了不对称光化学的新策略或超分子光化学的新概念，即生物分子的手性信息通过手性生物分子主体与前手性客体底物的溶液相超分子相互作用以及随后的UNI，以及由此产生的主客体络合物的双分子光化学反应，转移或倍增到光产物中。以修饰的环糊精、寡核苷酸、DNA、RNA和蛋白质为手性生物分子宿主的所有超分子光致化学方法都成功地以良好的光学产率产生了光学活性的光产物。因此，利用手性生物分子的超分子相互作用进行光化学不对称合成的最初想法已经被证明是一种新的光致手性方法学，并有可能推广到其他超分子体系。主要发现获得了…本论文的主要研究内容可概括如下：在不同温度下，研究了含显色团的环糊精敏化的环辛烯的不对称Z-to-E光异构化反应。事实上，天然b-环糊精中的(Z)-环辛烯在185 nm处直接照射得到的~lt；1%的较差Ee可显著提高到24%。双链DNA以及核苷和(寡聚)核苷酸首次被证明在水溶液中作为有效的手性光敏剂和/或手性光反应场来影响(Z)-环辛烯的对映分化光异构化。(S)-(+)-(E)-环辛烯与脱氧核糖核酸的光敏化最佳ee为15%。用d(T)_t；15&gt；d(A)_(t；15)&gt；作为光敏剂，得到的(R)-(E)-环辛烯的ee高达26%，而其他双链体的光敏化反应几乎得到外消旋的(E)-异构体。因此，碱基的组成和顺序是决定对映体选择性的重要因素，而连续的寡核苷酸序列是实现(Z)-环辛烯高对映体选择性光异构化所必需的。较少

In this study, the author has proposed a new strategy of asymmetric photochemistry or a new concept of supramolecular photochirogenesis, in which the chiral information of biomolecules is transferred to or multiplied in photoproducts through the solution-phase supramolecular interaction of chiral biomolecular hosts with prochiral guest substrates and the subsequent Uni, and bimolecular photochemical reactions of the resulting ,host-guest complexes. All of the examined supramolecular photochirogenic approaches, employing modified cyclodextrins, (oligo) nucleotides, DNA, RNA, and protein as chiral biomolecular hosts, were successful in creating optically active photoproducts in good optical yields. Thus, the original idea of using the supramolecular interactions of chiral biomolecules in photochemical asymmetric synthesis has been demonstrated to be useful as a novel photochirogenic methodology, and is potentially extended to the other supramolecular systems. The major findings obtained … More in this thesis may be summarized as follows.The enantiodifferentiating Z-to-E photoisomerization of cyclooctene included and sensitized by chromophoreappended cyclodextrins was investigated in aqueous solution at varying temperatures. Indeed, the original poor ee of <1 % obtained upon direct irradiation at 185 nm of (Z)-cyclooctene accommodated in native b-cyclodextrin was dramatically enhanced up to 24 % ee.The double stranded DNA, as well as nucleosides and (oligo)nucleotides, have been shown for the first time to function as effective chiral photosensitizers and/or chiral photoreaction field in aqueous solution to effect the enantiodifferentiating photoisomerization of (Z)-cyclooctene. The best ee of the chiral (E)-isomer produced upon, photosensitization with DNA was 15 % in favor of (S)-(+)-(E)-cyclooctene. (R)-(E)-cyclooctene was obtained in an ee as high as 26 % by using d(T)_<15> d(A) _<15> as a photosensitizer, whereas the photosensitizations by the other duplexes gave nearly racemic (E)-isomer. It is concluded therefore that the composition and the sequence of nucleobases are important factors in determinins the enantioselectivity, and the consecutive oligothymidine sequence is essential for realizing the highly enantioselectm photoisomerization of (Z)-cyclooctene. Less