Antioxidant and lipoxygenase inhibitory activities of boropinic acid, active principle of Boronia pinnata

Boropinic acid is a prenyloxy-cinnamic acid recently isolated from Boronia pinnata Sm., an Australian shrub belonging to the family of Rutaceae [1]. Like other prenyloxy-cinnamic and benzoic acids isolated from natural sources, few data about biological activity have been reported in the literature. Boropinic and other natural prenyloxy-cinnamic and benzoic acids, namely 4'-geranyloxy-p-coumaric acid, 4'-geranyloxy-ferulic acid, isolated from Acronychia baueri Schott [2], valencic acid, isolated from Citrus sinensis L. and Aegle marmelos Corr. [3] and 4-isopentenyloxy-vanillic acid, isolated from the liverwort Trichocolea lanata (Ehrh.) Dum. [4] were easily synthesized by a two-step sequence in high yield from the corresponding p-hydroxy aromatic acid and were assayed for radical scavenging activity using the DPPH test and for inhibition of enzymatic lipid peroxidation mediated by soybean 5-lipoxygenase. Compared to other acids and to known antioxidant compounds like BHT, Trolox and ascorbic acid, boropinic acid was by far more active in the lipoxygenase test (IC₅₀=7.6 ng/mL, p<0.05). The inhibition value recorded suggested that boropinic acid acted as an enzyme inhibitor rather than a mere radical or peroxide scavenger. This hypothesis was confirmed by studying the interaction between boropinic acid and soybean 5-lipoxygenase by molecular modeling techniques.

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