The briarellins, new eunicellin-based diterpenoids from a Caribbean gorgonian, Briareum asbestinum

seco-Briarellinone and Briarellin S, Two New Eunicellin-Based Diterpenoids from the Panamanian Octocoral Briareum asbestinum

“…Therefore the assignment of the planar structure of compound 1 was established as a novel seco -briarellin diterpene depicted in Figure 1. Comparison of the NMR data of compound 1 with previously reported seco -briarellins [1,4,7] evidenced the presence of the keto group at C-12 as a unique structural feature for compound 1 .…”

“…The spin system comprised by H-4, H-5, H-6 was confirmed by crossed correlations observed in correlation spectroscopy (COSY) experiments (Figure 2). The geometry of the C-4/C-5 double bond was assigned as trans on the basis of the coupling constant observed for protons H-4 and H-5 ( J H4,H5 = 15.6 Hz) [1]. …”

“…The briarellins are a family of tetracyclic diterpenes structurally derived from the eunicellin skeleton [1,2,3,4,5,6,7]. To date about 27 briarellins have been isolated and described from octocorals of the genus Briareum and Pachyclavularia .…”

“…To date about 27 briarellins have been isolated and described from octocorals of the genus Briareum and Pachyclavularia . A smaller group of eunicellin-related diterpenoids, composed by only three members, is known as seco -briarellins [1,4,7]. seco -Briarellins have a nine atom heterocycle across C-2/C-9 open at the C-6/C-7 bond as a main difference to the briarellin skeleton.…”

Bioactive (3Z,5E)-11,20-Epoxybriara-3,5-dien-7,18-olide Diterpenoids from the South China Sea Gorgonian Dichotella gemmacea

“…The C-2 glycoloyl group of 2 (δ H 4.15, d, J = 16.9 Hz and 4.03, d, J = 16.9 Hz; δ C 172.2, s, 61.1, t) was distinct from the analogously positioned acetoxy group of 7 (δ H 1.96, s; δ C 168.7, s and 21.3, q). In addition, the upfield-shifted C-16 signal of 2 (δ C 44.5) in the 13 C-NMR spectrum compared to that of 7 (δ C 72.2) together with the absence of the methoxy group (δ H 3.46, δ C 58.5) indicated the position of a chlorine atom at C-16 [32]. The location of the glycoloyl group at C-2 was confirmed by the HMBC correlations of both H-2′ and H-2 with C-1′.…”