ABSTRACT
Hyperpigmentation disorders are difficult to treat without causing permanent depigmentation or irritation. The most effective hypopigmenting agents are tyrosinase inhibitors, however some of those currently used have shown serious side effects. As several classes of flavonoids have already demonstrated ability to inhibit tyrosinase, a library of natural polymethoxyflavones isolated (1-7) from the bud exudate of Gardenia oudiepe and semi-synthetic derivatives (8,9) were evaluated. IC50 of the most active compounds were in the micromolar range. The strongest inhibitors 1, 2 and 3 all shared a 3',4'-dimethoxy-5'-hydroxy trisubstituted B ring. These SAR conclusions were confirmed by molecular docking studies. The mode of interaction with the enzyme was elucidated, and important interactions between the most active compounds and catalytic residues of tyrosinase were observed. All of these data provided a library of compounds as potential leaders for the design of new depigmenting agents and formulations.
Subject(s)
Enzyme Inhibitors/chemistry , Flavones/chemistry , Gardenia/chemistry , Monophenol Monooxygenase/antagonists & inhibitors , Agaricales/enzymology , Catalytic Domain , Enzyme Inhibitors/isolation & purification , Flavones/isolation & purification , Histidine/chemistry , Molecular Docking Simulation , Molecular Structure , Monophenol Monooxygenase/chemistry , Structure-Activity RelationshipABSTRACT
Xanthine oxidase (XO), an enzyme widely distributed among mammalian tissues, is associated with the oxidation of xanthine and hypoxanthine to form uric acid. Reactive oxygen species are also released during this process, leading to oxidative damages and to the pathology called gout. Available treatments mainly based on allopurinol cause serious side effects. Natural products such as flavonoids may represent an alternative. Thus, a series of polymethoxyflavones isolated and hemisynthesized from the bud exudates of Gardenia oudiepe has been evaluated for in vitro XO inhibitory activity. Compounds 1, 2 and 3 were more active than the reference inhibitor, Allopurinol (IC50 = 0.25 ± 0.004 µM) with IC50 values of (0.004 ± 0.001) µM, (0.05 ± 0.01) µM and (0.09 ± 0.003) µM, respectively. Structure-activity relationships were established. Additionally, a molecular docking study using MOE™ tool was carried out to establish the binding mode of the most active flavones with the enzyme, showing important interactions with its catalytic residues. These promising results, suggest the use of these compounds as potential leads for the design and development of novel XO inhibitors.