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.
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