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

Raola, Vamshi Krishna, Chakraborty, Kajal
Natural product research 2017 v.31 no.4 pp. 418-427
Rhizophora mucronata, antioxidant activity, inhibitory concentration 50, lipoxygenase, mass spectrometry, methanol, nuclear magnetic resonance spectroscopy, prostaglandin synthase, sesquiterpenoids, triterpenoids
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 (4 E , 8 Z)-3, 3a, 6, 7-tetrahydro-3, 9-dimethyl-5-(6-methylheptan-2-yl) cycloocta[b]furan-2-(9aH)-one (1). (35 E)-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 (IC ₅₀ ~ 0.75 mg/mL) compared to 2 (IC ₅₀ > 0.80 mg/mL). No significant differences in anti-cyclooxygenase-2 of these compounds were discernable (IC ₅₀ 0.8 – 0.9 mg/mL), whilst compound 1 showed greater anti-5-lipoxidase activities (IC ₅₀ ~ 0.8 mg/mL) those that of 2 (IC ₅₀ 0.96 mg/mL). Bioactivities of the prenylated terpenoids were inversely proportional to lipophilic and bulk descriptors.