Flavane Dimers From Psychotria calocarpa and Their Enzyme Inhibition Activities

Eight dimeric flavanes were isolated from the plant Psychotria calocarpa (Rubiaceae), including four stereoisomeric flavan-flavan-3-ol dimers (1-4) and four stereoisomeric flavan-3-ol-flavan-3-ol dimers (5-8). Among them, compounds 1-3 are newly identified flavan-(4→8)-flavan-3-ol dimers, named psychodiflavanols A-C, respectively. Their structures were elucidated by a comprehensive spectroscopic analysis combined with the quantum chemical calculations of electronic circular dichroism spectra. Compounds 4-8 were determined to be known flavan- (4→8)-flavan-3-ol dimer or flavan-3-ol-(4→8)-flavan-3-ol dimers based on comparison with literature data. All isolates were evaluated for their inhibitory activities against acetylcholinesterase, butyrylcholinesterase (BChE), α-glucosidase, and α-amylase. The results demonstrated that psychodiflavanol A (1) had potent and selective inhibition of BChE, with a half-maximal inhibitory concentration (IC₅₀) value of 11.47 ± 2.12 µM. In addition, psychodiflavanol B showed a notable α-glucosidase inhibitory effect with an IC₅₀ value of 10.15 ± 1.17 µM. These findings suggest that the flavane dimers from P. calocarpa might possess promising potential as lead compounds for developing therapeutic agents that target neurodegenerative and metabolic disorders.