Tengerensine (1), isolated as a racemate and constituted from a pair of bis-benzopyrroloisoquinoline enantiomers, and tengechlorenine (2), purified as a scalemic mixture and constituted from a pair of chlorinated phenanthroindolizidine enantiomers, were isolated from the leaves of Ficus fistulosa var. tengerensis, along with three other known alkaloids. The structures of 1 and 2 were determined by spectroscopic data interpretation and X-ray diffraction analysis. The enantiomers of 1 were separated by chiral-phase HPLC, and the absolute configurations of (+)-1 and (-)-1 were established via experimental and calculated ECD data. Compound 1 is notable in being a rare unsymmetrical cyclobutane adduct and is the first example of a dimeric benzopyrroloisoquinoline alkaloid, while compound 2 represents the first naturally occurring halogenated phenanthroindolizidine alkaloid. Compound (+)-1 displayed a selective in vitro cytotoxic effect against MDA-MB-468 cells (IC 7.4 μM), while compound 2 showed pronounced in vitro cytotoxic activity against all three breast cancer cell lines tested (MDA-MB-468, MDA-MB-231, and MCF7; IC values of 0.038-0.91 μM).

Two new monoterpenoid indole alkaloids, alstoscholactine (1) and alstolaxepine (2), were isolated from Alstonia scholaris. Compound 1 represents a rearranged stemmadenine alkaloid with an unprecedented C-6–C-19 connectivity, whereas compound 2 represents a 6,7-seco-angustilobine B-type alkaloid incorporating a rare γ-lactone-bridged oxepane ring system. Their structures and absolute configurations were determined by spectroscopic analyses. Compound 1 was successfully semisynthesized from 19E-vallesamine. Compound 2 induced marked vasorelaxation in rat isolated aortic rings precontracted with phenylephrine.

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Schwarzinicines A−G (1−7), representing the first examples of 1,4-diarylbutanoid−phenethylamine conjugates, were isolated from the leaves of Ficus schwarzii. The structures of these compounds were determined by detailed analysis of their MS, 1D and 2D NMR data. Compounds 1−4 exhibited pronounced vasorelaxant effects in the rat isolated aorta (E max 106−120%; EC 50 0.96−2.10 μM). However, compounds 1 and 2 showed no cytotoxic effects against A549, MCF-7, and HCT 116 human cancer cells (IC 50 > 10 μM).T he genus Ficus, belonging to the Ficeae tribe of the family Moraceae, comprises more than 750 species distributed in the tropical and subtropical regions of the world, with about 100 of the species occurring in Malaysia. 1 A number of Ficus species were reported to possess multiple ethnomedicinal uses including for the treatment of diarrhea, dysentery, skin diseases, diabetes, inflammation, ulcers, and cancer-related diseases. 2 To date, only eight Ficus species have been reported for their alkaloidal content, namely, F. hispida, 3−6 F. f istulosa, 7−9 F. f istulosa var. tengerensis, 10 F. septica, 11−14 F. nota, 15 F. hirta, 16 F. pachyrhachis, 17 and F. pantoniana, 18 suggesting that plants of this genus are still largely underinvestigated. This prompted us to explore Ficus species that occur in Peninsular Malaysia for alkaloids that possess interesting structures and/or useful biological activities. In addition to our previous investigations into the alkaloidal contents of F. hispida, 3 F. f istulosa, 7 and F. fistulosa var. tengerensis, 10 we also investigated Ficus schwarzii Koord., a tree that can grow up to 15 m in height and is widely distributed in southern Myanmar, Thailand, Peninsular Malaysia, Sumatra, and Borneo. 19 Herein, we report the isolation and structure elucidation of seven new 1,4-diarylbutanoid−phenethylamine conjugates, namely, schwarzinicines A−G (1−7) (Figure 1), from the leaves of F. schwarzii. The vasorelaxant effects of schwarzinicines A−D (1−4) in rat isolated aorta and cytotoxic effects of schwarzinicines A and B (1 and 4) against three human cancer cell lines are also reported.

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