Abstract
In an attempt to explore the bioactive metabolites of the soft coral Sarcophyton cinereum, three new cembranolides, cinerenolides A–C (1–3), and 16 known compounds were isolated and identified from the EtOAc extract. The structures of the new cembranolides were elucidated on the basis of spectroscopic analysis, and the NOE analysis of cinerenolide A (1) was performed with the assistance of the calculated lowest-energy molecular model. The relative configuration of cinerenolide C (3) was determined by the quantum chemical NMR calculation, followed by applying DP4+ analysis. In addition, the cytotoxic assays disclosed that some compounds exhibited moderate to potent activities in the proliferation of P388, DLD-1, HuCCT-1, and CCD966SK cell lines.
Highlights
As part of our continuing search for bioactive structures from marine soft corals [7–12], the chemical constituents from the soft coral Sarcophyton cinereum are investigated in this study
The EtOAc extract from S. cinereum was separated repeatedly by column chromatography and HPLC to afford three new diterpenoids (1–3) and 16 known compounds, which were identified as sarcophytonoxide E (4) [13], sarcomililatins A and B (5 and 6) [14], 2[(E,E,E)-70,80 -epoxy-40,80,120 -trimethylcyclotetradeca-10,30,110 -trienyl]propan-2-ol (7) [15], sarcophytonolide F (8) [16], cherbonolide L (9) [17], (+)-(2S)-isosarcophine (10) [18], (–)-(2R)isosarcophine (11) [19], sarcophytonoxide A (12) [13], sartrolide C (13) [20], ketoemblide
Its NMR data indicated that it is quite similar to the reduction products of sarcophytolide [21,25] (Tables 1 and 2); a secondary hydroxyl group is observed at δC 73.0 (CH) and δH 4.19 (1H, ddd, J = 11.0, 8.0, 4.0 Hz, H-5) for 1, revealing that one of the CH2 group in the cembranolide scaffold should be replaced by a hydroxycontaining methine
Summary
Soft corals of the genus Sarcophyton are a dominant species in many coral reef areas [1–3]. This species is well known to be a prolific producer of structurally unique diterpenes, especially cembranoids. As marine soft corals are a prolific source of bioactive cembranoids, investigations of promising structures with potent bioactivities have been persistently conducted in our laboratory. We report the isolation and structural elucidation of three new cembranolides with an α,β-unsaturated ε-lactone (1–3), as well as 16 related cembranoids (4–19). Their cytotoxicities against a limited panel of cancer cell lines are reported
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