4'-Hydroxy-6,7-methylenedioxy-3-methoxyflavone: A novel flavonoid from Dulacia egleri with potential inhibitory activity against cathepsins B and L.

A new flavone, 4'-hydroxy-6,7-methylenedioxy-3-methoxyflavone 1, and two other nucleosides, ribavirin 2 and adenosine 3, were isolated from the leaves of Dulacia egleri. The nucleosides were identified by spectroscopic techniques (1D, 2D-NMR) while the structure of the flavonoid was established by 1D, 2D-NMR analysis, including HRESIMS data. The results obtained in the biological assays showed that the compound 1 was able to inhibit cathepsins B and L with IC50 of 14.88 ±â€¯0.18 µM and 3.19 ±â€¯0.07 µM, respectively. The mechanism of inhibition for both enzymes were determined showing to be competitive at cathepsin B with Ki = 12.8 ±â€¯0.6 µM and non-linear non-competitive with positive cooperativity inhibition at cathepsin L with Ki = 322 ±â€¯33 µM, αKi = 133 ±â€¯15 µM, ßKi = 5.14 ±â€¯0.41 µM and γKi = 13.2 ±â€¯13 µM.