Isolation of a Morphinan Alkaloid and a Methoxybenzoic Acid with The Investigation on The Antibacterial Effect of Alphonsea cylindrica King Leaves

Abstract

Alphonsea cylindrica King belongs to the family Annonaceae, which is traditionally used to treat rheumatism, bruises, and edema. Investigation of its antibacterial properties was carried out on hexane and dichloromethane crude extracts using agar diffusion method and minimum inhibitory concentration against ESKAPE pathogens. Both extracts showed positive results in inhibiting E. faecium, S. aureus, and K. pneumoniae, while the dichloromethane extract showed further inhibition against P. aeruginosa. A morphinan alkaloid, O-methylpallidinine (1), along with a methoxybenzoic acid, isovanillic acid (2), were isolated from the dichloromethane leaf extract of the plant and elucidated via NMR spectroscopy, FTIR spectroscopy, UV-vis spectroscopy, and GC-MS, and compared with the reported data. Both compounds are reported for the first time from A. cylindrica, while O-methylpallidinine was isolated as natural product for the first time from the family Annonaceae. Both 1 and 2 showed low activity against S. aureus with an IC50 value of 371.82 μg/mL and 385.37 μg/mL, respectively. This is the first report on the antibacterial activity of compound 1. The results can be used as future references for the discovery of morphinans and the potential of A. cylindrica as an antibacterial source.