Design And Synthesis Of A Novel Chiral Pyridoxal / Pyridoxine Catalyst And Its Application In Asymmetric Trans

Optically active α-amino acids are a class of very important molecules. They are basic units of proteins and also broadly present in many natural products. In addition, α-amino acids also have been widely used as key chiral control elements in organic synthesis and asymmetric catalysis. Therefore development of new methods for the synthesis of α-amino acids is still an important and active topic in organic chemistry.In biological systems, enzymatic transamination of α-keto acids is the main process to sythesize various chiral amino acids. Vitamin B₆, i.e. the coenzyme of transaminases, serves as the catalysis center of biological transamination. The vitamin B₆ family includes pyridoxamine（PM）, pyridoxal（PL）, and the corresponding phosphates（PMP and PLP）. Development of asymmetric biomimetic transamination by using chiral pyridoxamines or pyridoxals as the catalyst may provide a new and efficient strategy for the synthesis of optically active amino acids.The studies include the following three parts:（1） A series of novel chiral pyridoxals and pyridoxamines have been developed by introducing a chiral five-membered ring to the pyridine skeleton. The catalysts are characterized with rigid backbone and short distantance between the catalysis center and the chiral center.（2） The chiral pyridoxamines/pyridoxals displayed good activity and high enantioselectivity in biomimetic transamination of α-keto acids to give a variety of optically active α-amino acids in 47-90% yields with up to 86% ee’s at room temperature in aqueous medium. The reaction exhibits some atrractive advantages such as higly mild conditions and easy operation.（3） A plausible mechanistic pathway has been proposed for the transamination and a reasonable transition state model has also been suggested for understanding the origin of the chirality.