Undescribed triterpenoid ellagitannins from Castanopsis calathiformis and their potential antiproliferative and hypoglycemic activity.

Triterpenoid ellagitannins containing diphenoyl moiety were endemic to Castanopsis. Nine triterpenoid ellagitannins, namely six undescribed triterpenoid ellagitannins (1-6) and three known analogues 23,24-di-O-galloyl-2α,3β,23,24-tetrahydroxyolean-12-en-28-oic acid 28-O-β-d-glucopyranoside (7), castanopsinin F (8), 3,24-(S)-hexahydroxydiphenoyl-23-O-galloyl-2α,3β,23,24-tetrahydroxyurs-12-en-28-oic acid (9), were isolated from Castanopsis calathiformis (Skan) Rehder & E. H. Wilson in Sarg. Compounds 1-2 and 4 were undescribed triterpenoid ellagitannins containing triphenoyl group instead of diphenoyl group. Compounds 5 and 6 were triterpenoid ellagitannins bearing an unusual tricyclic cage-like structure. Elucidation of their structures was performed through comprehensive spectroscopic analysis, with absolute configurations determined by analysis of electronic circular dichroism spectroscopy data and electronic circular dichroism calculations. Bioactivity evaluation revealed that compounds 1-4, 8 and 9 exhibited potent α-glucosidase inhibitory activity with IC values ranging from 22.8 to 73.3 μM, surpassing that of the positive control acarbose (IC = 1616.0 μM). In addition, The compounds 1, 4 and 6 were evaluated for antiproliferative activity against five human tumor cell lines including A549 (lung cancer), HCT116, HeLa, HepG2 and MCF-7, compound 4 displayed a mild antiproliferative activity against MCF-7 cell line.