!Two new C-benzylated dihydrochalcone derivatives, 4,2′,4′-trihydroxy-6′-methoxy-3′(2′′-hydroxybenzyl)dihydrochalcone(1) and 2′,4′-dihydroxy-4,6′-dimethoxy-3′(2′′-hydroxybenzyl)dihydrochalcone (2), along with six known flavonoid derivatives (3-8), a known dihydrochalcone dimer (9), three known aromatic esters (10-12), and one known aromatic amide (13), were isolated from the leaves of Melodorum siamensis. The structures of the compounds were elucidated by spectroscopic analysis, mainly 1D and 2D NMR techniques ( 1 H,
13C, COSY, HMQC, and HMBC), as well as by comparison with literature data. The isolated compounds with a sufficient amount for biological assays were evaluated for their antimalarial, antimycobactirial, and cytotoxic activities. Compounds 1, 2, and 13 exhibited strong cytotoxicity against human tumor cell lines KB and NCI-H187, with IC 50 values in the range of 0.66-7.16 µg/mL.
Key wordsMelodorum siamensis · Annonaceae · antimycobacterial activity · antimalarial activity · cytotoxic activity Supporting information available online at http://www.thieme-connect.de/ejournals/toc/plantamedica The genus Melodorum (Annonaceae) comprises 55 species, which grow in tropical Asia [1]. Two species have been phytochemically investigated. The aporphine alkaloids were isolated from a mixed sample of M. punctulatum leaves and bark [2]. Several cytotoxic butenolides were isolated from the leaves of M. fructicosum [3,4] and two oxidized heptanes were found in the flowers of the same plant [5]. In the course of our continuing search for bioactive constituents from Thai medicinal plants, a preliminary screening of the ethyl acetate extract of the leaves of Melodorum siamensis (Scheff.) Ban revealed cytotoxicity against human epimermoid carcinoma (KB), human breast cancer (MCF7), and human small cell lung cancer (NCI-H187) cell lines with IC 50 values of 1
