Two rare antioxidative prenylated terpenoids from loop-root Asiatic mangrove <i>Rhizophora mucronata</i> (Family Rhizophoraceae) and their activity against pro-inflammatory cyclooxygenases and lipoxidase

<p>Two new biogenic prenylated terpenoids were isolated from the methanol extract of <i>Rhizophora mucronata.</i> The extended C₂₀ sesquiterpenoid with prenylated guaiane framework was characterised as (4<i>E</i>, 8<i>Z</i>)-3, 3a, 6, 7-tetrahydro-3, 9-dimethyl-5-(6-methylheptan-2-yl) cycloocta[b]furan-2-(9aH)-one (<b>1</b>). (35<i>E</i>)-1,2,3,5,6,6-icosahydro-4,4,8b,10,14,17,20,20-octamethylpicen-3-yl-34,35-dimethyloct-31-enoate (<b>2</b>) represents the first example of naturally occurring C₄₀ prenylated oleanane-type triterpenoid, whereas one 4,5-dimethyloct-5-enoate side chain remains attached at C-3 position of the oleanane framework formed by the E-ring closure of C₃₀ saccharide moiety. The structures of the compounds were elucidated using NMR and mass spectrometric analysis. Compound <b>1</b> was found to have significantly greater antioxidant activities (IC₅₀ ~ 0.75 mg/mL) compared to <b>2</b> (IC₅₀ > 0.80 mg/mL). No significant differences in anti-cyclooxygenase-2 of these compounds were discernable (IC₅₀ 0.8 – 0.9 mg/mL), whilst compound <b>1</b> showed greater anti-5-lipoxidase activities (IC₅₀ ~ 0.8 mg/mL) those that of <b>2</b> (IC₅₀ 0.96 mg/mL). Bioactivities of the prenylated terpenoids were inversely proportional to lipophilic and bulk descriptors.