Absolute configuration by vibrational circular dichroism of anti-inflammatory macrolide briarane diterpenoids from the Gorgonian Briareum asbestinum

The four new briarane diterpenoids 2-butyryloxybriarane B-3 ( 2 ), 9-acetylbriarenolide S ( 3 ), briarenolide W ( 4 ), and 12-isobriarenolide P ( 5 ), along with briarane B-3 ( 1 ) and the five known diterpenes 6–10 were isolated from the gorgonian coral Briareum asbestinum collected from the Mexican Caribbean Sea . The structures were elucidated by 1D and 2D NMR and MS measurements. Since the structure of briarane B-3 ( 1 ) was only suggested and published without any spectroscopic support, it was herein confirmed, and the supporting data are now provided. In addition, 1 provided the opportunity to explore the sensitivity of vibrational circular dichroism (VCD) to determine the configuration of a single stereogenic center in the presence of eight other stereogenic centers in a molecule possessing a highly flexible ten-member ring. A single-crystal X-ray diffraction study, in which the Flack and Hooft parameters of 1 were determined, further confirmed that briarane B-3 is (1 S ,2 S ,6 S ,7 R ,8 R ,9 S ,10 S ,11 R ,17 R )- 1 . This paper reports for first time the use of VCD in briarane diterpenes and with the presence of chlorine atoms. Biological evaluation of seven isolated compounds evidenced a moderate anti-inflammatory activity for compounds 6 and 9 but it did not show any cytotoxic, antiviral, antibacterial, and topoisomerase inhibitory activity.