Wada Takehiko, Nishijima Masaki, Fujisawa Tai, Sugahara Norimitsu, Mori Tadashi, Nakamura Asao, Inoue Yoshihisa
Department of Molecular Chemistry, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan.
J Am Chem Soc. 2003 Jun 25;125(25):7492-3. doi: 10.1021/ja034641g.
Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxyalate (AC) was performed at 25 degrees C in aqueous buffer solution (pH 7) in the presence of bovine-serum albumin (BSA) to afford four [4 + 4] cyclodimers, i.e., anti- and syn-head-to-tail (HT) (1 and 2) and anti- and syn-head-to-head (HH) dimers (3 and 4), of which only 2 and 3 are chiral. We found that (1) BSA possesses four sets of binding sites for AC of different affinities, stoichiometries, and chiral environment for photoreaction, which bind 1, 3, 2, and 3 AC molecules with binding constants of 5.3 x 107, 1.3 x 105, 1.4 x 104, and 3.0 x 103 M-1, respectively, (2) the regioselectivity of photodimerization is switched from HT to HH by adding BSA (the HH/HT ratio varies from 0.28 to 4.3), (3) BSA-mediated photodimerization of AC affords optically active products 2 and 3 of up to 29% and 41% ee, respectively. It is emphasized that the selective excitation of bound substrate, utilizing the spectral shift upon complexation with BSA, is not a prerequisite for efficient photochirogenesis using biomolecules.
在25℃下，于pH 7的水性缓冲溶液中，在牛血清白蛋白（BSA）存在的条件下，对2-蒽甲酸酯（AC）进行对映体选择性光环二聚反应，得到四种[4 + 4]环二聚体，即反式和顺式头对尾（HT）（1和2）以及反式和顺式头对头（HH）二聚体（3和4），其中只有2和3是手性的。我们发现：（1）BSA具有四组对AC具有不同亲和力、化学计量比和光反应手性环境的结合位点，它们分别以5.3×10⁷、1.3×10⁵、1.4×10⁴和3.0×10³ M⁻¹的结合常数结合1、3、2和3个AC分子；（2）通过添加BSA，光二聚反应的区域选择性从HT切换为HH（HH/HT比值从0.28变化到4.3）；（3）BSA介导的AC光二聚反应分别得到高达29%和41% ee的光学活性产物2和3。需要强调的是，利用与BSA络合时的光谱位移对结合底物进行选择性激发，并非使用生物分子进行高效光致手性生成的先决条件。
