Antioxidants from Xylocarpus granatum

Abstract

Xylocarpus granatum Koeg. (Meliaceae) is growing in mangrove forests in Southeast Asia, tropical Australia and East Africa The bark has been used in traditional medicine to treat diarrhea, cholera, fever and abdominal troubles, and it is well known for its astringent properties. Chemically, the tree contains a number of xyloccensins (triterpenoids of limonoid type). Content of tannins has also been reported, but their chemical structures appear to be unknown. The aim of this study was to isolate and identify chemical substances from X. granatum and to evaluate the DPPH radical scavenging activity and the inhibitory effect towards 15-lipoxygenase (15-LO). Total phenolic content was quantified by the Folin Ciocalteu method. X. granatum was collected in the Sundarbans mangrove forest in Bangladesh. The 80% methanol extract of the stem bark was suspended in distilled water and successively extracted with chloroform, ethyl acetate and n-butanol. The extracts were fractionated by different chromatographic techniques, compounds were identified by NMR and by degradation with phloroglucinol/HCl. High amounts of procyanidins in addition to the monomeric compounds catechin and epicatechin were isolated. The structures of the procyanidins were procyanidin B1 (epicatechin (4β→8) catechin), epicatechin (4β→8) epicatechin (4β→8) catechin and epicatechin (4β→8) epicatechin (4β→8) epicatechin (4β→8) epicatechin (4β→8) catechin. The limonoids gedunin, xyloccensin O, xyloccensin P and xyloccensin Q were isolated, as well. The procyanidins showed high DPPH radical scavenging and 15-LO inhibitory activities, whereas the limonoids were inactive as radical scavengers and showed only weak inhibition of 15-LO.