Isolation, Structural Elucidation, and Biological Evaluation of Homoisoflavonoids From Pterolobium Macropterum

Three new mimosin-type homoisoflavonoids (1, 3, 4) and a new sappanin-type homoisoflavonoid (5), together with eight known homoisoflavonoids, were isolated from the methanol extract of the twigs and leaves of Pterolobium macropterum. Compound 1 is a rare tetranor-homoisoflavonoid. The structures of all isolates were elucidated by comprehensive spectroscopic interpretation. The anti-proliferative activity against JIMT-1 cells and the antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA003), Acinetobacter baumannii, and Bacillus cereus of compounds 1-12 were evaluated. As a result, compound 2 showed excellent anti-proliferative activity against JIMT-1 cells with an IC₅₀ of 1.08 µM, and potently inhibited the colony formation of JIMT-1 cells at 2.0 µM. Furthermore, compounds 11 and 12 (MIC = 32 µg/mL) exhibited broad-spectrum antibacterial activity against the abovementioned bacterial strains by regulating the ROS level. Preliminary structure-activity relationship (SAR) analysis of these homoisoflavonoids revealed that the α,β-unsaturated moieties are crucial for both anti-proliferative and antibacterial activities.