Activity-guided isolation of the chemical constituents of Muntingia calabura using a quinone reductase induction assay

Activity-guided fractionation of an EtOAc-soluble extract of the leaves of Muntingia calabura collected in Peru, using an in vitro quinone reductase induction assay with cultured Hepa 1c1c7 (mouse hepatoma) cells, resulted in the isolation of a flavanone with an unsubstituted B-ring, (2 R,3 R)-7-methoxy-3,5,8-trihydroxyflavanone ( 5), as well as 24 known compounds, which were mainly flavanones and flavones. The structure including absolute stereochemistry of compound 5 was determined by spectroscopic (HRMS, 1D and 2D NMR, and CD spectra) methods. Of the isolates obtained, in addition to 5, (2 S)-5-hydroxy-7-methoxyflavanone, 2′,4′-dihydroxychalcone, 4,2′,4′-trihydroxychalcone, 7-hydroxyisoflavone and 7,3′,4′-trimethoxyisoflavone were found to induce quinone reductase activity. A flavanone with an unsubstituted B ring, (2 R,3 R)-7-methoxy-3,5,8-trihydroxyflavanone, as well as 24 known compounds, were isolated from an EtOAc-soluble extract of the leaves of Multingia calabura. All isolates were evaluated for their potential cancer chemopreventive properties using a quinone reductase induction assay.