Cytotoxicity-guided phytochemical investigation of a methanolic extract of Croton tonkinensis afforded two new kaurane diterpenoids (1, 2) and 10 known ent-kaurane-type diterpenoids (3- 12). The structures of 1 and 2 were based on analysis of spectroscopic and mass spectral data. Compounds 3- 12 were identified by comparison of their spectroscopic and physical data with those reported in the literature. Selected compounds from this plant were examined for cytotoxic and anti-inflammatory activities. Compounds 4 and 9 showed the highest cytotoxic activity against the tested tumor cell lines. Compounds 3, 4, 6, 8, 9, and 11 had IC 50 values less than 5 microM and were more potent than the nonspecific NOS inhibitor L-NAME in inhibiting LPS-induced NO production.

Previous studies on the chemical constituents of sea whip gorgonian corals belonging to the genus Junceella and Ellisella (family Ellisellidae), collected in waters off Taiwan, yielded a series of interesting briarane diterpenoids. Briarane-type natural products are found only in marine organisms and mainly from octocorals. [27][28][29] Compounds of this type are suggested to be originally synthesized by host corals, 4,30) and confirmed to possess various bioactivities. 27-29)We have further isolated a new chlorinated briarane, fragilide J (1), from the sea whip gorgonian coral Junceella fragilis. Furthermore, two chlorinated briaranes, including a new compound, robustolide L (2), and a known metabolite, robustolide H (3), 24) were obtained from the sea whip gorgonian coral Ellisella robusta. In this paper, we describe the isolation, structure determination, and bioactivity of the above briaranes 1-3. Results and DiscussionFragilide J from J. fragilis Fragilide J (1) was isolated as a white powder. The molecular formula of 1 was estab- ). The IR spectrum of 1 showed bands at 3491, 1790, and 1741 cm Ϫ1 , consistent with the presence of hydroxy, g-lactone, and ester carbonyl groups. The 13 C-NMR and distortionless enhancement by polarization transfer (DEPT) spectra of 1 showed that this compound has 26 carbons (Table 1) H correlation spectroscopy (COSY) spectrum of 1, five different structural units, C-2/-3/-4, C-6/-7, C-9/-10, C-12/-13/-14, and C-17/-18, were identified (Table 1), which were assembled with the assistance of a heteronuclear multiple-bond coherence (HMBC) experiment (Table 1). The HMBC correlations between protons and quaternary carbons of 1, such as H-9, H-10, H 3 -15/C-1; H-4/C-5; H-4, H-17, H 3 -18/C-8; H-9, H-10, H 2 -12/C-11; and H-17, H 3 -18/C-19, permitted the elucidation of the carbon skeleton of 1. An exocyclic double bond at C-5 was confirmed by the allylic coupling between H-6 and H 2 -16 in the 1 H-1 H COSY experiment and by the HMBC correlations between H 2 -16/C-4, -6. The ring junction C-15 methyl group was positioned at C-1 A new chlorinated briarane, fragilide J (1), has been isolated from the sea whip gorgonian coral Junceella fragilis. In addition, the sea whip gorgonian coral Ellisella robusta yielded two chlorinated briaranes, including a new compound, robustolide L (2), and a known metabolite, robustolide H (3). The structures of these compounds were determined using spectroscopic methods. The structure, including the absolute configuration of 3, was further confirmed by X-ray data analysis for the first time.