New cassane butenolide hemiketal diterpenes from the marine creeper Caesalpinia bonduc and their antiproliferative activity

Two new cassane butenolides, caesalpinolide A (1) and B (2), epimeric at the hemiketal position were isolated from the marine creeper Caesalpinia bonduc. The structures were elucidated by the analysis of spectroscopic data and relative stereochemistry was assigned on the basis of ROESY correlations. Compounds 1 and 2 were found to inhibit MCF-7 breast cancer cell lines with IC50 values of (μM) 12.8 and 6.1, respectively, along with the inhibition of endometrial and cervical cancer cell lines.