Cytotoxic Components from the Bark of Stauranthus perforatus from Monteverde, Costa Rica

Bark samples from several individuals of the understory tree, Stauranthus perforatus Liebm. (Rutaceae) [1], were collected (May, 1997) from lower montane moist forest at ca. 1350 m a.s.l. at Monteverde, Costa Rica (10°18′N, 84°48′W). A voucher specimen has been deposited with the Museo Nacional de Costa Rica and the Missouri Botanical Garden (William Haber collection number 4922). The stem bark (1.698 kg) was macerated and extracted with dichloromethane (4 h) to give 11.31 g extract. The crude extract showed in-vitro cytotoxic activity against Hep-G2 (human hepatocellular carcinoma) [2] and MDA-MB-231 (human mammary adenocarcinoma) [3] cells (Table [1]). The extract (9.53 g) was subjected to bioactivity-directed flash chromatography; silica gel (230 - 400 mesh), 82 cm L × 5 cm D, hexane/ethyl acetate step gradient (hexane, 9 : 1 hexane/EtOAc, 4 : 1 hexane/EtOAc, 1 : 1 hexane/EtOAc, EtOAc; Fig. [1]), detection of eluates by TLC. The cytotoxic compounds proved to be the quinoline alkaloids skimmianine (424.6 mg) [4] and veprisine (44.9 mg) [5], and the furocoumarin heraclenin (80.2 mg) [6] (Table [1]). The structure of skimmianine was determined by single-crystal X-ray diffraction [4]. Other compounds isolated: β-sitosterol (106 mg) [7], isopimpinellin (118.6 mg) [8], and xanthotoxin (32.3 mg) [9]. Structures of these compounds were determined by comparison of ¹H-NMR with those reported in the literature. Information in detail on the work-up procedure and X-ray crystal structure are obtainable from the author of correspondence.

Skimmianine is apparently a ubiquitious alkaloid in the Rutaceae. It has been isolated from many members of the family including Skimmia japonica, Fagara spp., Glycosmis pentaphylla, and Ruta graveolens [10]. Skimmianine has shown anti-leishmanial activity [11], anti-platelet aggregation activity [12], and is a serotonin antagonist [11]. Unfortunately, this compound is also mutagenic [13].

Fig. 1Chromatographic separation of Stauranthus perforatus bark extract.

Table 1Cytotoxic activity of Stauranthus perforatus bark and components. Cytotoxicity (LC50) Material Hep-G2 MDA-MB-231 S. perforatus crude bark extract 91.84 (± 1.81) % kill at 250 μg/mL 100 % kill at 250 μg/mL Skimmianine 38.7 (± 3.1) μM 146 (± 55) μM Veprisine 130 (± 55) μM 203 (± 19) μM Heraclenin 60.1 (± 31.0) μM 184 (± 51) μM Isopimpinellin 537 (± 451) μM > 1000 Xanthotoxin 439 (± 8) μM > 1000 β-Sitosterol > 600 > 600 Paclitaxel 58.7 (± 24.0) μM 20.1 (± 7.7) μM Vinblastine 1.19 (± 0.67) μM 9.23 (± 7.89) μM

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