[Abstract] 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 (1S,2S,6S,7R,8R,9S,10S,11R,17R)-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.This work was supported by Grants RTI2018-093634-B-C22 (AEI/FEDER, EU) from the State Agency for Research (AEI) of Spain, co-funded by the FEDER Programme from the European Union. We thank to Xunta de Galicia for the support of Grants GRC2018/039 and ED431E 2018/03 for CICA-INIBIC strategic group and BLUEBIOLAB (o474_BLUEBIOLAB_1_E, Programme INTERREG V A of Spain-Portugal (POCTEP). JR, CJ, and D.P.-P. acknowledge CESGA for the use of the computational facilities. PJ-N acknowledges partial financial support from CONACYT-Mexico Grant No. 284194. D.P.-P. received a postdoctoral fellowship from the National Council of Science and Technology (CONACYT) of Mexico. The work was also supported by UIDB/50006/2020 with funding from FCT/MCTES through national fundsXunta de Galicia; GRC2018/039Xunta de Galicia; ED431E 2018/03México. Consejo Nacional de Ciencia y Tecnología; 284194Portugal. Fundação para a Ciência e a Tecnologia; UIDB/50006/202
