Potential anti-inflammatory phenolic glycosides from the medicinal plant Moringa oleifera fruits

Abstract

Bioassay-guided isolation and purification of the ethyl acetate extract of Moringa oleifera fruits yielded three new phenolic glycosides; 4-[(2′- O-acetyl-α- l-rhamnosyloxy) benzyl]isothiocyanate ( 1), 4-[(3′- O-acetyl-α- l-rhamnosyloxy)benzyl]isothiocyanate ( 2), and S-methyl- N-{4-[(α- l-rhamnosyloxy)benzyl]}thiocarbamate ( 3), together with five known phenolic glycosides ( 4– 8). The structures of the new metabolites were determined on the basis of spectroscopic analyses including 1D- and 2D-NMR and mass spectrometry. The anti-inflammatory activity of isolated compounds was investigated with the lipopolysaccharide (LPS)-induced murine macrophage RAW 264.7 cell line. It was found that 4-[(2′- O-acetyl-α- l-rhamnosyloxy)benzyl]isothiocyanate ( 1) possessed potent NO–inhibitory activity with an IC 50 value of 1.67 μM, followed by 2 (IC 50 = 2.66 μM), 4 (IC 50 = 2.71 μM), and 5 (IC 50 = 14.4 μM), respectively. Western blots demonstrated these compounds reduced LPS-mediated iNOS expression. In the concentration range of the IC 50 values, no significant cytotoxicity was noted. Structure–activity relationships following NO-release indicated: (1) the isothiocyanate group was essential for activity, (2) acetylation of the isothiocyanate derivatives at C-2′ or at C-3′ of rhamnose led to higher activity, (3) un-acetylated isothiocyanate derivatives displayed eight times less activity than the acetylated derivatives, and (4) acetylation of the thiocarbamate derivatives enhanced activity. These data indicate compounds 1, 2, 4 and 5 are responsible for the reported NO-inhibitory effect of Moringa oleifera fruits, and further studies are warranted.