Secondary metabolites from the unripe fruits of Persea americana and their anti-tubercular activity
Persea americana Mill. (Lauraceae) is an evergreen tree, distributed in tropical and subtropical regions around the world. Until now, the bark, leaves, fruits and seeds of P. americana have been extensively studied. Previous studies on this plant identified various classes of chemical constituents, such as monoterpenoids, sesquiterpenoids, triterpenoids, aliphatics, lignans, flavonoids and alkaloids. From the previous investigations, this plant showed numerous bioactivities, including cytotoxicity, antifungal, antibacterial, acetyl-CoA carboxylase inhibition, nitric oxide and superoxide generation inhibition, and liver injury suppressing. Approximately 1200 species of Formosan plants have been screened for antitubercular activity against Mycobacterium tuberculosis H37Rv in vitro, and the methanolic extract of the unripe fruits of P. americana was shown with antitubercular activity. The aims of this study are the isolation of chemical constituents and their antitubercular activity. The methanolic extract of the unripe fruits of P. americana was partitioned into ethyl acetate and water-soluble layers. Bioassay-guided fractionation of the ethyl acetate-soluble layer has led to the isolation of four new aliphatic alcohols: avocadenols A-D (1-4), together with three known compounds: 1,2,4-trihdroxyheptadec-16-ene (5), 1,2,4-trihydroxyheptadec-16-yne (6), and 1,2,4-trihydroxynonadecane (7). The structures of these isolates were elucidated by spectroscopic analysis. 1,2,4-Trihdroxyheptadec-16-ene (5) and 1,2,4-trihydroxyheptadec-16-yne (6) have showed antitubercular activity against M. tuberculosis H37Rv in vitro with MIC values of 35.7 and 60.5µg/mL, respectively. The isolation of the unripe fruits and the antitubercular assay of the isolates are still in progress.