Kalihioxepanes A—G: Seven Kalihinene Diterpenoids from Marine Sponge Acanthella cavernosa Collected off the South China Sea

Abstract

Seven new kalihinene diterpenoids, kalihioxepanes A-G (1-7) bearing a rare oxepane ring, were isolated from sponge Acanthella cavernosa collected from the South China Sea. The structures and absolute configurations were elucidated by comprehensive spectroscopic analysis, single crystal X-ray diffraction, and quantum chemical calculation methods. Kalihioxepane A (1) displayed strong cytotoxicity against H69 and K562 tumor cells, while kalihioxepane B (2) showed moderate cytotoxicity against K562 cells.

Clavukoelloids A—M, Thirteen Rare N‐Containing Nardosinane Type Sesquiterpenoids from the Soft Coral Clavularia koellikeri

“…The relative configuration of compound 9 was supported as 4 S *,5 R *,7 S * through the NOESY correlations of H 3 ‐14/H 3 ‐15, together with the NMR shift calculations and DP4+ probability. [ 16‐17 ] The ECD calculations supported the absolute configuration of 9 to be 4 S ,5 R ,7 S .…”

“…Each pair of epimers addressed in this study ( i.e ., 2 vs. 3 , 4 vs. 5 ) was used for the validation process employing GIAO NMR chemical shift calculations coupled with CP3. [ 15‐16 ] This strategy has been extensively applied in structural validation and revision when the NMR spectra of a pair of diastereomers are available. The CP3 analysis supported the NMR‐based assignments produced for each pair of epimers ( i.e ., 2 vs. 3 , 4 vs. 5 ) with 100% probability when both the 1 H and 13 C NMR chemical shift values were considered.…”

“…The relative configuration of compound 9 was supported as 4S*,5R*,7S* through the NOESY correlations of H 3 -14/H 3 -15, together with the NMR shift calculations and DP4+ probability. [16][17] The ECD calculations sup-ported the absolute configuration of 9 to be 4S,5R,7S. Clavukoelloid J (10) was isolated as colorless oil, and its molecular formula was C 17 H 25 NO 4 based on HRESIMS.…”

Sinudenoids A–E, C19-Norcembranoid Diterpenes with Unusual Scaffolds from the Soft Coral Sinularia densa

“…The enhancement of H-5 was observed after irradiation of H-4, implying the relative configuration of C-4 in 5 was different from that in 6. The single-crystal X-ray diffraction experiment with 5 (Figure 4, Cu Kα radiation) determined the absolute configuration of 5 as 1R,4R,5S,8R,10S,11S [Flack parameter of 0.04 (15)], indicating 5 and 6 are epimers at C-4.…”

“…They were thought to originate from the common C 19norcembranoid diterpene precursor, norrubifolide, through different cyclization processes. 12,13 In our continuing search for new bioactive metabolites from marine invertebrates, 14,15 the first systematic investigation for the soft coral Sinularia densa collected off the Xisha Islands (Paracel Islands) resulted in the isolation of four unprecedented furanobutenolide-derived C 19 -norcembranoids, sinudenoids A− D (1−4, respectively) with three different types of carbon scaffolds, one rare 8/8 bicyclic sinudenoid E (5), and four known related compounds, sinuscalide A (6), 16 5-episinuleptolide (7), 17 scabrolide B (8), 18 and scabrolide A (9) (Figure 1). 18 The first analogue of sinudenoid E (5) as a co-isolate in this work, sinuscalide A (6), was just published in July 2022.…”