Flavonoids from the root of Muntingia calabura with inhibitory activity on superoxide generation and elastase release by neutrophils

Muntingia calabura L. (Tiliaceae) is an evergreen tree, distributed in tropical America and introduced in southern Taiwan as a cultivated plant. M. calabura is commercially used as healthcare products for the improvement of hypertension, myocardial infarction, spasm, and inflammatory conditions. Its fruits can be processed into jam and the leaves can be used for making tea. This plant is rich in flavonoids with flavones, flavanones, flavans, and biflavans as the major constituents, some of which have demonstrated cytotoxic and anti-platelet aggregation activities. In our studies on the anti-inflammatory constituents of Formosan plants, many species have been screened for in vitro inhibitory activity on neutrophil pro-inflammatory responses, and M. calabura has been found to be an active species. Two new biflavans, (M),(2S),(2′′S)-,(P),(2S),(2′′S)-8,8′′-dihydroxy-7,3′,4′,5′,7′′,3′′′,4′′′,5′′′-octamethoxy-5,5′′-biflavan (1) and (M),(2S),(2′′S)-,(P),(2S),(2′′S)-7,8,3′,4′,5′,7′′,8′′, 3′′′,4′′′,5′′′-decamethoxy-5,5′′-biflavan (2), and a new flavone, 4′-hydroxy-7,8,3′,5′-tetramethoxyflavone (3) have been isolated from the root of M. calabura, together with 9 known compounds. The structures of these new compounds were determined through spectroscopic and MS analyses. Among the isolated compounds, 7-hydroxyflavanone exhibited potent inhibition with IC₅₀ value of 4.92 ± 1.71µM against fMLP-induced superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP).

Acknowledgement: This research was supported by grants from the National Science Council (NSC, Taiwan) (No. NSC 98 – 2320-B-127 – 001-MY3 and NSC 101 – 2320-B-127 – 001-MY3), awarded to Prof. J.-J. Chen.