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.
Highlights
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
In the course of our ongoing chemical research on bioactive marine natural products[15,16,17,18], in particular diterpenes from marine sources[19,20,21,22,23,24], and from those collected in the Yucatan peninsula (Mexico)[25], we focused our attention on the soft coral B. asbestinum because it was assumed to be a rich source of briarane diterpenoids
The presence of one chlorine atom became evident from the [M + Na]+ cluster ion peaks at m/z 505/507, in a 3:1 ratio, observed in the Low resolution electrospray mass spectrometry (LRESIMS)
Summary
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 first structural elucidation of briarein A isolated from B. asbestinum in 19778, more than 500 briarane-type secondary metabolites have been reported from Octocorallia Subclass, including Gorgonacea, Pennatulacea, Alcyonacea and Stolonifera Orders. Some of these compounds displayed biological activities such as cytotoxic, antiviral, anti-inflammatory, immunomodulatory, antifouling and ichthyotoxic[9,10,11,12,13,14].
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