Uncommon Capnosane Diterpenes with Neuroprotective Potential from South China Sea Soft Coral Sarcophyton boettgeri

Abstract

The first investigation of the South China Sea soft coral Sarcophyton boettgeri afforded five new capnosane diterpenes, sarboettgerins A–E (1–5), together with one known related compound, pavidolide D (6). Their structures, including absolute configurations, were elucidated by the extensive spectroscopic analysis, 13C NMR calculations, and X-ray diffraction. Among them, new compounds 1–5 were featured by the rarely encountered Z-geometry double bond Δ1 within the 5/11-fused bicyclic capnosane carbon framework. Plausible biogenetic relationships of all isolates were proposed, and they might give an insight into future biomimetic synthesis of these novel compounds. In an in vitro bioassay, compound 5 displayed potent anti-neuroinflammatory activity against LPS-induced NO release in BV-2 microglial cells, which might be developed as a new type of potential neuroprotective agent in future.

Two New Cembranoids from the Chinese Soft Coral Sarcophyton boettgeri**

“…It is interesting to note that the uncommon capnosane diterpenes, biogenetically derived from cembranoids through transannular cyclization or ring rearrangement, presented in our previous collection in Weizhou Island [6] but did not be found in the present study. Based on the discrepancy, further research should be conducted to understand the different metabolic formation patterns among diverse metabolites and their actual ecological roles in the life cycle of soft corals.…”

“…[4,5] To our knowledge, among all of the reported species of Sarcophyton, there have been no reports regarding the chemical constituents of the title soft coral Sarcophyton boettgeri, except for our two studies in 2022. It is interesting to note that we discovered five uncommon capnosane diterpenes with neuroprotective potency from the title animal collected off the Weizhou Island, Guangxi Zhuang Autonomous Region, China, [6] whereas four new polyoxygenated cembranoids not present in Guangxi collection were obtained from the same species in Ximao Island, Hainan Province, China. [7] Recently, we have encountered S. boettgeri in Weizhou Island.…”

Structurally Diverse Diterpenes from the South China Sea Soft Coral Sarcophyton trocheliophorum

“…Thus, the relative configuration of 5 could be assigned as 3 R * ,4 R * ,13 S * ,14 S * based on the extensive analysis of the NOESY spectrum. Meanwhile, the relative configuration of 5 could also be elucidated via QM-NMR protocol by using the DP4+ method, which has become one of the most popular and reliable methods to find the most likely structure from a set of putative candidates [ 34 , 47 ]. Four possible isomers (2 R *,3 R *,13 R *,14 S *)- 5a , (2 R *,3 R *,13 S *,14 S *)- 5b , (2 R *,3 S *,13 R *,14 S *)- 5c and (2 R *,3 S *,13 S *,14 R *)- 5d ( Table S3 ) were subjected to QM-NMR calculations.…”

“…Moreover, terpenes display rich structural diversities, which could be further categorized as sesquiterpenes [ 17 , 18 , 19 ], diterpenes [ 20 , 21 , 22 , 23 , 24 ], and biscembranoids [ 21 , 25 , 26 , 27 , 28 ]. Moreover, these metabolites exhibit a wide spectrum of biological activities, including anti-angiogenic [ 17 ], antimicrobial [ 27 , 29 ], cytotoxic [ 29 , 30 ], anti-inflammatory [ 27 , 31 ], immunomodulatory [ 25 ], antifouling [ 8 , 32 ], and neuroprotective [ 33 , 34 ] effects. The intriguing chemical and biological properties of terpenes have led to extensive attention from global researchers [ 35 ].…”

Oxygenated Cembrane Diterpenes from the South China Sea Soft Coral Sinularia tumulosa**

“…To define the relative configurations of C-1 and C-15, quantum mechanical-NMR (QM-NMR) calculations using DP4 + probability analysis were performed, which is a popular and widely used method for the stereochemical studies of natural products. [25,26] Because the main concern of the configuration was the cis/trans orientations for H-1 and H 3 -17, (1R*,15R*)-2 and (1R*,15S*)-2 were selected as two possible candidate diastereoisomers and then subjected to QM-NMR calculations. As a result, the experimentally observed NMR data of 2 gave the best match of 100 % to the 1R*,15R* conformer (Figure S4.1).…”