Oxidative burst inhibition, cytotoxicity and antibacterial acriquinoline alkaloids from Citrus reticulate (Blanco)

Two novel acridone-quinoline alkaloids, acriquinoline A (1) and acriquinoline B (2), together with twenty-two known compounds were isolated from the methanol extract of the root of Citrus reticulata Blanco. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR and mass spectral (EI and ESI) data. The possible biosynthesis for the formation of above compounds is proposed, based on close examination of their structures. Compounds 1, 2, 6, 10 and 14-17 exhibited strong suppressive effect on phagocytosis response upon activation with serum opsonized zymosan in the range of IC50 0.2-10.5μM, which was tested in vitro for oxidative burst studies of whole blood. However, compounds displayed low cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3, with IC50 between 30.8 and 60.5μM compared to the standard doxorubicin with IC50 0.9μM. These compounds, tested against bacteria, fungi and plant pathogen oomycetes by the paper disk agar diffusion assay, resulting in missing to low activities corresponding with MICs>1mg/mL.