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

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.

A Holistic Approach to Determining Stereochemistry of Potential Pharmaceuticals by Circular Dichroism with β-Lactams as Test Cases

“…In recent times CD, in its electronic and vibrational ranges (ECD and VCD, respectively), is becoming an increasingly important and productive research tool because it effectively determines the absolute configuration, conformation, and optical purity of chiral molecules. This is evidenced by, for example, the constantly growing number of literature reports on its practical and successful use, such as these few newest links indicated here [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

Marine natural products

“…575 Four new examples of briarane-type diterpenoids, 2-butyryloxybriarane B-3 1336, 9-acetylbriarenolide S 1337, briarenolide W 1338 and 12-isobriarenolide P 1339, were isolated from a Yucatan Peninsula collection of Briareum asbestinum. 576 In addition, the previously reported MNP briarane B-3 was also isolated, with the authors using a combination of VCD, which is the rst reported use of this technique to study this class of NP, and XRD to provide further conrmation of the absolute conguration recently determined using 1 H NMR residual chemical shi anisotropy. 577 Collections of B. stechei (synonymous with B. excavatum) afforded a range of structurally-related diterpenes including briarenols L 1340 (Ie Island), 578 O 1341, P 1342 (aquaculture), 579 U 1343, V 1344 (Ie island), 580 W 1345, X 1346, Y 1347 and Z 1348 (aquaculture) 581 and briastecholides A-C 1349-1351 (Ie Island).…”

A Survey of Recently Discovered Naturally Occurring Organohalogen Compounds

“…In addition, the previously suggested briarane-3 (120) structure has now been confirmed. 47 A South China Sea collection of Ellisella sp. led to the discovery of 12 briaranes, including two new chlorine-containing metabolites, ellisellolides B (121) and H (122).…”

“…A specimen of Briareum asbestinum from the Mexican Caribbean Sea contains the new chlorinated briarane diterpenoids 117 – 119 . In addition, the previously suggested briarane-3 ( 120 ) structure has now been confirmed . A South China Sea collection of Ellisella sp.…”