Development Of Chiral Pyridoxal/pyridoxamine Quaternary Ammonium Salt Catalysts And Their Applications In Biomimetic Catalysis

Vitamin B6 is an important coenzyme for many enzymes and it has exerted powerful catalysis capability in biological system.For example,Vitamin B6 can catalyze transamination for synthesis of chiral amino acids and it also catalyzes aldol addition of glycine to aldehydes for synthesis chiral ?-hydroxy-?-amino acids.Considering the exclusive catalysis power shown by Vitamin B6 in biological system,imitation of Vitamin-B6-based enzymes for asymmetric catalysis is potentially attractive and also is a big challenge in organic synthesis.In this thesis,we focused on development chiral N-quaternized pyridoxals/pyridoxamines and their application in biomimetic asymmetric catalysis.The work includes the following two parts.(1)We developed a variety of N-quaternized chiral pyridoxamines with biary backbone.The N-quaternized chiral pyridoxamines display high catalytic activity(1-2 mol% catalyst loading)and excellent enantioselectivity in biomimetic asymmetric transamination of ?-keto acids,to give various chiral ?-amino acids in 80-99 yields with 84-96% ee's.(2)We developed a class of new large steric hinderance branch N-quaternized chiral pyridoxals with biary backbone.Studies indicate that the N-quaternized chiral pyridoxals can catalyze asymmetric Mannich addition of glycine ester to Ts-imines to give ?,?-diaminoacid esters in moderate yields with up to 93% ee.The reaction has imitates the enzyme-catalyzed asymmetric aldol addition of glycine to aldehydes in biological system.