AbstractTwo new isoquinoline alkaloids, iraqiine (1) and kareemine (2), along with five known alkaloids, muniranine (3), kinabaline (4), O-methylmoschatoline (5), atherospermidine (6) and N-methylouregidione (7), were purified from the dichloromethane crude extract of Alphonsea cylindrica bark. The structures of these compounds were elucidated through extensive 1D and 2D NMR, IR and LC–MS studies and comparison with previously reported data. Compounds (1–5 and 7) were tested for their antioxidant activity using in vitro DPPH radical scavenging assay, and 1, 3 and 4 showed the highest antioxidant activities with IC50 values of 48.77 ± 1.01, 44.51 ± 1.12 and 64.28 ± 0.93 μg/ml, respectively
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