Paliasanines A-E, 3,4-Methylenedioxyquinoline Alkaloids Fused with a Phenyl-14-oxabicyclo[3.2.1]octane Unit from Melochia umbellata var. deglabrata.

Five new quinoline alkaloids, paliasanines A-E (1-5), and 17 known compounds (6-22) were isolated from a methanol extract of Melochia umbellata var. deglabrata leaves. Their chemical structures were elucidated by analysis of HRMS and 1D and 2D NMR spectroscopic data. Compounds 1-5 are the first naturally occurring 3,4-methylenedioxyquinolines incorporating an oxabicyclo[3.2.1]octane unit. Compounds 6 and 7 displayed selective cytotoxicity (IC50 5.9-8.4 μM) against A549 and MCF-7 cell lines, while compounds 1-5 were not active. Compounds 1-3 did not exhibit an anti-HIV effect in MT4 cells, although the related quinolone derivative waltherione A exhibited significant activity. These preliminary results indicate that the 3-methoxy-4-quinolone skeleton might be preferred for both antiproliferative and anti-HIV activities.