Nuxia oppositifolia is traditionally used in diabetes treatment in many Arabian countries; however, scientific evidence is lacking. Hence, the present study explored the antidiabetic and antioxidant activities of the plant extracts and their purified compounds. The methanolic crude extract of N. oppositifolia was partitioned using a two-solvent system. The n-hexane fraction was purified by silica gel column chromatography to yield several compounds including katononic acid and 3-oxolupenal. Antidiabetic activities were assessed by α-amylase and α-glucosidase enzyme inhibition. Antioxidant capacities were examined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) scavenging assays. Further, the interaction between enzymes (α-amylase and α-glucosidase) and ligands (3-oxolupenal and katononic acid) was followed by fluorescence quenching and molecular docking studies. 3-oxolupenal and katononic acid showed IC50 values of 46.2 μg/mL (101.6 µM) and 52.4 μg/mL (119.3 µM), respectively against the amylase inhibition. 3-oxolupenal (62.3 µg/mL or 141.9 μM) exhibited more potent inhibition against α-glucosidases compared to katononic acid (88.6 µg/mL or 194.8 μM). In terms of antioxidant activity, the relatively polar crude extract and n-butanol fraction showed the greatest DPPH and ABTS scavenging activity. However, the antioxidant activities of the purified compounds were in the low to moderate range. Molecular docking studies confirmed that 3-oxolupenal and katononic acid interacted strongly with the active site residues of both α-amylase and α-glucosidase. Fluorescence quenching results also suggest that 3-oxolupenal and katononic acid have a good affinity towards both α-amylase and α-glucosidase enzymes. This study provides preliminary data for the plant’s use in the treatment of type 2 diabetes mellitus.

One new cytotoxic steroid, dendronesterone A (1), two new steroids, dendronesterones B and C (2 and 3), and a known steroid (4) were isolated from the methylene chloride solubles of the Formosan soft coral Dendronephthya gigantea. Two cytotoxic ylangene-type sesquiterpenoids, lemnalol (5) and the new compound cervicol (6), as well as two ylangene-type sesquiterpenoids, isolemnalol (7) (a new compound) and 4-oxo-alpha-ylangene (8), were isolated from the methylene chloride solubles of the Formosan soft coral Lemnalia cervicorni. Their structures were elucidated by 1D and 2D NMR spectral analysis, and their cytotoxicity against selected cancer cells was measured in vitro.

Five new nardosinane sesquiterpenoids, armatins A-E, lemnal-1(10)-ene-2,12-dione (a new natural product), and two new cytotoxic 19-oxygenated ergosterols, armatinols A and B, were isolated from the methylene chloride extract of the soft coral Nephthea armata, collected in Taiwan. The structures were elucidated by 1D and 2D NMR spectral analysis, and their cytotoxicity was determined against selected cancer cells.