B Type and Complex A/B Type Epicatechin Trimers Isolated from Litchi pericarp Aqueous Extract Show High Antioxidant and Anticancer Activity.
Int J Mol Sci. 2018 Jan 19 ;19(1). Epub 2018 Jan 19. PMID: 29351247
Litchi (Sonn.) fruit is known for its rich source of phenolics.contains high levels of epicatechin that may form oligomers of various lengths. Except for several A or B type epicatechin dimers, other soluble oligomers have rarely been identified in the pericarp. Here, bioassay-guided column fractionation was applied to isolate bioactive phenolics from aqueous pericarp extract. A fraction (S3) was obtained by two rounds of Sephadex LH-20 column chromatography, and showed higher antioxidant activity and inhibition on the proliferation of human lung cancer cells (A549) than. S3 was further separated to isolate fractions P1-P4, which all showed higher antioxidant activity than vitamin C. P3 showed 32.9% inhibition on A549 cells at 30μg/mL, higher than other fractions and-Dichlorodiamineplatinum (DDP, 0.5μg/mL), but not as high as the combination of the four fractions. Using HPLC-Q-TOF-MS/MS, one B-type and complex A/B type epicatechin trimers were identified in P3; another B-type and two A/B-type trimers were identified in P4. P1 and P2, containing epicatechin and proanthocyanidin B2, respectively, showed no cell inhibition at 30 μg/mL. It is the first time that the two B type trimers of epicatechins (Litchitannin B1 and B2), have been found in Litchi species. The identified proanthocyanidins were detected in the pericarp of the young fruit, and the levels of the compounds decreased as thefruit developed, correlating to the decreasing patterns of the expression ofand, two key genes in the catechin biosynthesis pathway.