Cytotoxic and antimalarial biflavonoids isolated from the aerial parts of Ochna serrulata (Hochst.) Walp

Abstract

This paper reports the phytochemistry and biological activities (antimalarial and cytotoxicity) of compounds isolated from aerial parts of Ochna serrulata. Silica gel chromatography followed by repeated chromatotron on the stem bark extract of the plant yielded a new dimeric chalcone (5-deoxyurundeuvine C) along with lophirone C, lophirone A, afzelone B, epicatechin, methyl (2 €²,4 €²-dihydroxyphenyl)acetate and a mixture of campylospermone A and isocampylospermone A. From the leaves extract, ochnaflavone, 2 €³,3 €³-dihydroochnaflavone, vitexin-6 €³-O-acetate, 3 €²-methoxyvitexin-6 €³-O-acetate and (2 €²,4 €²-dihydroxyphenyl)acetic acid were isolated and characterized. A cyanoglucoside was isolated from an extract of flowers and fruits of the plant. The proposed structures of the respective new and known compounds were assigned by using 1D and 2D NMR techniques as well as Mass spectrometry. The cytotoxicity activity of the compounds was tested using sulforhodamine B (SRB) assay in three different cancer cell lines namely, UACC62 (melanoma), TK 10 (renal), and MCF7 (breast). Ochnaflavone and 3 €²-methoxyvitexin-6 €³-O-acetate inhibited the growth of UACC62 at TGI (Total Growth Inhibition concentration) 12.91 and 14.11 µM, respectively. The cytotoxic activities of lophirone C were found to be TGI = 35.63, 11.67 and 30.35 µM, against TK, UACC62 and MCF7 cancer cells respectively. Lophirone A exhibited TGI against these cancer cells at 58.96, 26.23 and 40.01 µM, respectively. The rest of the compounds exhibited no significant cytotoxicity against the three cancer cells. Moreover, the compounds were evaluated for antimalarial activity against FCR-3 (chloroquine-resistant Plasmodium falciparum) strains. Ochnaflavone demonstrated the highest activity IC₅₀  = 17.25 µM, followed by lophirone A (29.78 µM), 5-deoxyurundeuvine C (31.07 µM), lophirone C (35.31 µM), afzelone B (39.54 µM), 2 €³,3 €³-dihydroochnaflavone (61.86 µM) and 3 €²-methoxyvitexin-6 €³-O-acetate (106.35 µM). These results concur with the traditional use of the genus in the treatment of various ailments.

Keywords:          5-Deoxyurundeuvine C, Biflavonoid, Cytotoxicity, Antimalarial,  Ochna serrulata