Tirosinase inhibitors are important to treat abnormal pigmentation disorders. The prenylated flavanones from Sophora flavescens (Leguminosae) were reported to inhibit tyrosinase activity. (1,2) In our continuous work with native bioactive plants we study Argentinean species of the Dalea genus. A previous study about the biological activity of the hexane extract of Dalea boliviana Britton roots showed inhibitory activity on the tyrosinase enzyme as well (66,74�}9,11% of inhibition at concentration100ƒÊg/ml) In order to find the secondary metabolites responsible for this activity, we deepened the chemical study of that bioactive extract. We have already reported the isolation of three prenylflavonoids: two chromeno flavanones (2S)-5,2´-dihydroxy-3´-prenyl-6´´,6´´ dimethylchromeno- (7, 8, 2´´, 3´´) - flavanone (1); (2S) -5-hydroxy-6´´, 6´´ dimethylchromeno- (7, 8, 2´´, 3´´)-flavanone (2) and (2S)-5,7,2´-trihydroxy-8,3´-diprenyl-flavanone (3). Compounds 1 and 3 were reported for the first time in bibliography. (3,4) We herein report the isolation and structural characterization of a new prenylated flavanone: (2S)-5,7,2´-trihydroxy- 8 - prenyl-5´- (1 ´´´,1 ´´´-dimethylallyl) - flavanone (4). This structure was elucidated by application of various spectroscopic methods, mainly 1D and 2D NMR spectroscopy.
Compounds 3 and 4 were examined on their inhibitory effect against tyrosinase activity based on Rahman et al. method (5) adapted to the present work conditions. Quercetine was used as the reference inhibitor. The samples degree inhibition was expressed as % of Inhibition.
The obtained results were 58,01±2,09% for compound 3 (100 µg/mL) and 52,0±0,24% for compound 4 (100 µg/mL), respectively.
