Abstract
Five new cembrane-type diterpenoids, lobocrassins A–E (1–5), were isolated from the soft coral Lobophytum crassum. The structures of cembranes 1–5 were established by spectroscopic and chemical methods and by comparison of the spectral data with those of known cembrane analogues. Lobocrassin A (1) is the first cembranoid possessing an α-chloromethyl-α-hydroxy-γ-lactone functionality and is the first chlorinated cembranoid from soft corals belonging to the genus Lobophytum. Lobocrassins B (2) and C (3) were found to be the stereoisomers of the known cembranes, 14-deoxycrassin (6) and pseudoplexaurol (7), respectively. Lobocrassin B (2) exhibited modest cytotoxicity toward K562, CCRF-CEM, Molt4, and HepG2 tumor cells and displayed significant inhibitory effects on the generation of superoxide anion and the release of elastase by human neutrophils.
Highlights
Among the diterpenoids isolated from octocorals, the cembrane-type metabolites are the largest group of compounds [1], and the soft coral Lobophytum crassum has been proven to be a rich source of cembrane-type compounds [2,3,4,5,6,7,8,9,10,11,12,13]
To the best of our knowledge, lobocrassin A (1) is the first cembranoid possessing an α-chloromethyl-α-hydroxy-γ-lactone functionality, and this compound is the first chlorinated cembranoid from soft corals belonging to the genus Lobophytum
After evaporation of excess reagent, the residue was separated by column chromatography on silica gel to give pure lobocrassin D (4) (n-hexane/EtOAc, 20:1, 3.3 mg, 97%); physical (Rf and optical rotational values) and spectral (IR, 1H, and 13C NMR) data were in full agreement with those of natural product 4
Summary
Among the diterpenoids isolated from octocorals, the cembrane-type metabolites are the largest group of compounds [1], and the soft coral Lobophytum crassum (family Alcyoniidae) has been proven to be a rich source of cembrane-type compounds [2,3,4,5,6,7,8,9,10,11,12,13]. In our continuing research on novel substances from the octocorals distributed in the waters of Taiwan at the intersection of the Kuroshio current and the South China Sea surface current, the soft coral L. crassum was studied to determine the properties of its organic extract, which displayed cytotoxicity toward MCF-7 (human breast adenocarcinoma) and HeLa (human cervical carcinoma) cells (IC50 = 10.2 and 8.8 μg/mL, respectively). Lobocrassins A–E (1–5) (Figure 1), were isolated. We report the isolation, structure determination, and bioactivity of cembranes 1–5
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