Abstract:
Hyper-pigmentation of the skin is a common problem that is prevalent in middle aged and elderly
people. It is caused by over production of melanin. Tyrosinase is known to be the key enzyme in
melanin production. Ethanolic extract of Greyia flanaganii leaves showed significant (P < 0.05) antityrosinase
activity exhibiting the IC50 of 32.62 g/ml. The total extract was further investigated for
its toxicity and effect on melanin production by melanocytes cells, and showed significant inhibition
(P < 0.05) (20%) of melanin production at 6.25 g/ml and low levels of cytotoxicity (IC50 < 400 g/ml).
The amount of antioxidants necessary to decrease the initial DPPH absorbance by 50% (EC50) by the
total ethanolic extract was found to be 22.01 g/ml. The effect of G. flanaganii against acne causing
bacteria, Propionibacterium acnes, was investigated using microdilution assay. The MIC of the
extract of G. flanaganii was found to be 250 g/ml. Bioassay-guided fractionation led to the isolation
of (3S)-4-hydroxyphenethyl 3-hydroxy-5-phenylpentanoate (1), 2 ,4 ,6 -trihydroxydihydrochalcone (2),
2 ,6 ,4-trihydroxy-4 -methoxydihydrochalcone (3), 2 ,6 -dihydroxy-4 -methoxydihydrochalcone (4), 5,7-
dihydroxyflavanone [(2S)-pinocembrin] (5), 2 ,6 -dihydroxy-4 ,4-dimethoxy dihydrochalcone (6) and
(2R,3R)-3,5,7-trihydroxy-3-O-acetylflavanone (7). The isolated compounds were tested for their antioxidant,
cytotoxicity, tyrosinase inhibition and antibacterial activities. Compound 2 exhibited significant
(P < 0.05) antityrosinase activity exhibiting the IC50 of 69.15 M. The isolated compounds showed low toxicity
of the cells with reduction of melanin content of the cells. All compounds tested showed good radical
scavenging activity. These data indicates that G. flanaganii extract and its isolated phenolic constituents
could be possible skin lightening agents.