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

Two new biogenic prenylated terpenoids were isolated from the methanol extract of Rhizophora mucronata. The extended C-20 sesquiterpenoid with prenylated guaiane framework was characterised as (4E, 8Z)-3, 3a, 6, 7-tetrahydro-3, 9-dimethyl-5-(6-methylheptan-2-yl) cycloocta[b] furan-2-(9aH)-one (1). (35E)-1,2,3,5,6,6-icosahydro-4,4,8b, 10,14,17,20,20-octamethylpicen- 3-yl-34,35-dimethyloct-31-enoate (2) represents the first example of naturally occurring C-40 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 C-30 saccharide moiety. The structures of the compounds were elucidated using NMR and mass spectrometric analysis. Compound 1 was found to have significantly greater antioxidant activities (IC50 similar to 0.75 mg/mL) compared to 2 (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 1 showed greater anti-5-lipoxidase activities (IC50 similar to 0.8 mg/mL) those that of 2 (IC50 0.96 mg/mL). Bioactivities of the prenylated terpenoids were inversely proportional to lipophilic and bulk descriptors. [GRAPHICS] .