Highly Aromatic Flavan-3-ol Derivatives from Palaeotropical Buch.-Ham Possess Radical Scavenging and Antiproliferative Properties.

Phytochemical investigation of leaves and stembark of collected in Thailand resulted in three yet undescribed isomeric flavan-3-ol derivatives (-), the four known compounds gambircatechol (), (+)-catechin (), (+)-afzelechin () and the stilbene oxyresveratrol (). Compounds to feature 6/6/5/6/5/6 core structures. All structures were deduced by NMR and MS, while density functional theory (DFT) calculations on B3LYP theory level were performed of compounds to to support the stereochemistry in positions 2 and 3 in the C-ring. Possible biosynthetic pathways leading to are discussed. The DPPH assay revealed high radical scavenging activities for (EC = 9.4 ± 1.0 µmol mL), (12.2 ± 1.1), (10.0 ± 1.5) and (19.0 ± 2.6), remarkably lower than ascorbic acid (EC = 34.9) and α-tocopherol (EC = 48.6). A cytotoxicity assay revealed moderate but consistent antiproliferative properties of in CH1/PA-1 (ovarian teratocarcinoma) and SW480 (colon carcinoma) cells, with IC values of 25 ± 6 and 34 ± 4 µM, respectively, whereas effects in A549 (non-small cell lung cancer) cells were rather negligible. The performed DCFH-DA assay of in the former cell lines confirmed potent antioxidative effects even in the cellular environment.