Department of Life Sciences and Chemistry, Jacobs University Bremen GmbH, Campus Ring 1, 28759, Bremen, Germany.
Department of Biochemical Engineering, Graduate School of Science and Technology, Yamagata University, Yonezawa, Yamagata, 992-8510, Japan.
ChemistryOpen. 2020 Jan 29;9(1):93-96. doi: 10.1002/open.201900343. eCollection 2020 Jan.
Four differently substituted chiral Ni(II)-complexes of dehydroalanine Schiff base were prepared and reacted with BrCFCOOEt/Cu under the standard reaction conditions. The observed diastereoselectivity was found to depend on the degree and pattern of chlorine substitution for hydrogen in the structure of the dehydroalanine complexes. The unsubstituted complex gave the ratio of diastereomers ()(2)/()(2) of 66/34. On the other hand, introduction of chlorine atoms in the strategic positions on the chiral ligands allowed to achieve a practically attractive diastereoselectivity of (∼98.5/1.5). Diastereomerically pure major product was disassembled to prepare 9-fluorenylmethyloxycarbonyl (Fmoc) derivative of ()-4,4-difluoroglutamic acid.
四种不同取代的手性 Ni(II)-去氢丙氨酸席夫碱配合物被制备出来，并在标准反应条件下与 BrCFCOOEt/Cu 反应。观察到的非对映选择性取决于去氢丙氨酸配合物中氢的氯取代程度和模式。未取代的配合物给出了非对映异构体 ()(2)/()(2)的比例为 66/34。另一方面，在手性配体的战略位置上引入氯原子，使得实现了具有实际吸引力的非对映选择性（约为 98.5/1.5）。非对映异构体纯的主要产物被拆开，以制备 ()-4,4-二氟谷氨酸的 9-芴甲氧羰基（Fmoc）衍生物。
