Cyclized 9,11-secosterol enol-ethers from the gorgonian Pseudopterogorgia americana

•Three new 9,11-secosterols 1-3 were isolated from Pseudopterogorgia americana.•Compounds 1 and 2 are sterols bearing a seven-membered cyclic enol-ether in ring C.•Compounds 3 is the first 9,11-secosterol containing a C-24(28) double bond.•The results presented can be used for further synthetic and pharmacological studies.

Chemical investigation of the MeOH extract from the gorgonian Pseudopterogorgia americana afforded two rare sterols, ameristerenol A (1) and B (2), both 9,11-secosterols possesses a seven-membered cyclic enol-ether in ring C, and ameristerol A (3) is the first example of a naturally occurring 9,11-secosterol containing a gorgosterol side chain with a C-24(28) double bond. Ameristerenol A (1) was converted to the sterol derivatives 4-6 to provide additional chemical diversity and comparison for biological screening. The structures of compounds 1-6, along with three related known analogues 7-9, were determined on the basis of extensive spectroscopic analysis and by comparison with literature data. Compound 6 exhibited slight cytotoxicity activity against human breast cancer cell line MDA-MB-231.

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