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-alpha-l-rhamnosyloxy) benzyl]isothiocyanate (1), 4-[(3'-O-acetyl-alpha-l-rhamnosyloxy)benzyl]isothiocyanate (2), and S-methyl-N-{4-[(alpha-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-alpha-l-rhamnosyloxy)benzyl]isothiocyanate (1) possessed potent NO-inhibitory activity with an IC(50) value of 1.67 microM, followed by 2 (IC(50)=2.66 microM), 4 (IC(50)=2.71 microM), and 5 (IC(50)=14.4 microM), 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.