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

Abstract 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 IC 50 of 14.88 ± 0.18 μM and 3.19 ± 0.07 μM, respectively. The mechanism of inhibition for both enzymes were determined showing to be competitive at cathepsin B with Ki  = 12.8 ± 0.6 μM and non-linear non-competitive with positive cooperativity inhibition at cathepsin L with K i = 322 ± 33  μ M, α K i  = 133  ±  15 μ M , β K i  =  5.14 ± 0.41  μ M and γ K i  = 13.2  ± 13  μ M.