Abstract
A tyrosinase inhibitor was isolated from the whole plant of
Barbarea orthocerus Led. (Brassicaceae) by activity-guided fractionation,
and identified as (R)-5-phenyl-2-oxazolidinethione
(barbarin) by structural analysis followed by comparison with reported spectral
data. The compound exhibited significant inhibitory effects on mushroom and
murine tyrosinases at more than 1.6 × 10-5 M.
Barbarin exhibited IC50 values of 4.2 × 10-5 M
on mushroom tyrosinase and of 4.8 × 10-5 M on
murine tyrosinase. Kojic acid as a positive control exhibited IC50
values of 3.4 × 10-5 M and 6.0 × 10
-5 M on mushroom and murine tyrosinases, respectively.
Therefore, barbarin exhibited a similar level of inhibitory potency with kojic
acid used as a positive control. In a kinetic study with various concentrations
of L-dopa as the substrate, barbarin was identified as an uncompetitive inhibitor
and kojic acid as a mixed inhibitor of both mushroom and murine tyrosinases.
Barbarin exhibited KEIS values of 3.3 × 10-5 M
and 3.6 × 10-5 M on mushroom and murine tyrosinases,
respectively. Kojic acid exhibited KEIS and KEI values
of 2.4 × 10-5 M and 2.2 × 10-5 M
on mushroom tyrosinase and those of 8.9 × 10-5 M
and 7.2 × 10-5 M on murine tyrosinase, respectively.
Key words
Barbarea orthocerus Led. - Brassicaceae - barbarin - mushroom and murine tyrosinases - uncompetitive inhibitor
