Brianthein A, a novel briarane-type diterpene reversing multidrug resistance in human carcinoma cell line, from the gorgonian Briareum excavatum

A novel briarane-type diterpene named brianthein A (1), which has been isolated from the gorgonian Briareum excavatum, reversed multidrug resistance (MDR) in human carcinoma cell lines, KB-C2, overexpressing P-glycoprotein (P-gp). The absolute stereostructure of 1 was elucidated by the detailed 2D-NMR analysis of 1 and the application of the modified Mosherʹs method to the partially deacetylated derivative of 1. Furthermore, novel analogous compounds, briantheins B (8) and C (9), were also isolated from the same gorgonian. From the structure-activity relationship study, each of the 2, 3 and 14-acetoxyl groups and 11,12-olefin in 1 were found to be crucial for the MDR reversing activity.