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Photocatalytic Synthesis of Pipecolic Acid from Lysine on TiO2: Effects of the Structure of Catalysts and Adsorbed Species on Chiral Selectivity
Organic Process Research & Development ( IF 3.4 ) Pub Date : 2018-10-26 00:00:00 , DOI: 10.1021/acs.oprd.8b00299
Yuxin Zhai 1 , Steven S. C. Chuang 1
Affiliation  

A one-step photocatalytic synthesis of l-pipecolic acid (l-PCA) from l-lysine (l-Lys) has been investigated by in situ infrared (IR), circular dichroism, and 1H NMR spectroscopy. Chiral selectivity toward l-Lys was found to be governed by the structure of adsorbed l-Lys and the structure of TiO2. Both anatase and rutile were not able to catalyze the reaction in a solvent-free environment. In situ IR studies revealed that l-Lys adsorbed on these TiO2 in a dicationic form of which the positive −NH3+ functional groups are not able to interact with photogenerated holes. Interestingly, P-25 TiO2, which contains 80 wt % anatase and 20 wt % rutile, adsorbs l-Lys in a zwitterionic form, allowing its hydrogen in the α-amino group to be abstracted by the photogenerated hole, producing racemic PCA. The addition of H2O as a solvent allowed l-Lys to be adsorbed on P-25 in an anionic form, producing l-PCA as a major product. This study demonstrates that the reaction environment has a direct impact on the structure of adsorbed species that controls the selectivity of a chiral synthesis.

中文翻译:

赖氨酸对TiO 2的光催化合成哌考酸:催化剂和吸附物种结构对手性选择性的影响。

已经通过原位红外(IR),圆二色性和1 H NMR光谱研究了从l-赖氨酸(l -Lys)一步合成光催化的1- pipecolic acid(l -PCA)的方法。发现对l -Lys的手性选择性受吸附的l -Lys的结构和TiO 2的结构支配。在无溶剂的环境中,锐钛矿和金红石都不能催化该反应。原位红外研究表明,l -Lys以指示性形式吸附在这些TiO 2上,其正-NH 3 +官能团不能与光生空穴相互作用。有趣的是,含有80 wt%的锐钛矿和20 wt%的金红石的P-25 TiO 2以两性离子形式吸附l- Lys,使得其α-氨基中的氢被光生空穴提取,生成外消旋PCA。加入H 2 O作为溶剂可使1 - Lys以阴离子形式吸附在P-25上,从而产生1- PCA作为主要产物。这项研究表明,反应环境对控制手性合成选择性的吸附物质的结构具有直接影响。
更新日期:2018-10-26
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