Enantioselective synthesis and antimicrobial activities of tetrahydro-β-carboline diketopiperazines.

A series of single isomers tetrahydro-β-carboline diketopiperazines were stereoselectively synthesized starting from l-tryptophan methyl ester hydrochloride and six aldehydes through a four-step reaction including Pictet-Spengler reaction, crystallization-induced asymmetric transformations (CIAT), Schotten-Baumann reaction, and intramolecular ester amidation. The chemical structures were characterized by nuclear magnetic resonance (NMR) and elemental analysis, among which two compounds were determined by x-ray single crystal diffraction. Moreover, antimicrobial activities of all the compounds were also tested.