Bio-active sesquiterpenoids and norsesquiternoids from the Red Sea octocoral Rhytisma fulvum fulvum

Abstract

Three previously undescribed nardosinane-type sesquiterpenes (1–3), together with six known compounds (4–9) were isolated from the alcyonacean soft coral Rhytisma fulvum fulvum.2 and 3 are 13-nornardosinane, and 6,7-seco-13-nornardosinane derivatives, respectively. 2 could be an artifact due to C-6 epimerization of the known one 4. Chemical structures were elucidated based on 1 D, 2 D NMR and MS spectral data. Compounds 1-8 showed cytotoxic activity against NCI-H1299, HepG2 and MCF-7 with IC50 values between 0.0352–0.0974, 0.0717–0.3745 and 0.0341–0.1325 mM, respectively. The antibacterial activity of all isolated compounds have examined against a number of Gram-positive (Bacillus cereus, Staphylococcus aureas) and Gram-negative (Escherichia coli, Klebsiella pneumoniae and Pseudomonas sp.) bacteria. Compounds 6 and 7 showed a high degree of inhibition against B. cereus, S. aureus and Pseudomonas sp. Interestingly, neolemnane (6) showed strong inhibition against two fungi, Aspergillus niger and Fusarium oxysporum; while 8 showed positive inhibition against Fusarium oxysporum at 150 µg/mL.