Research Letter: New Potent Indole Derivatives as Hyaluronidase Inhibitors

Abstract

Because of the physiologic importance of hyaluronidases, the identification of potent and selective inhibitors of hyaluronidases has become increasingly important. A variety of assay methods have been used for such a purpose, i.e. classical turbidimetric, viscometric and colorimetric. In this study, a modified enzymatic assay has been used to obtain a microtiter plate‐based sensitive activity screening. All inhibitors were tested in a stains‐all assay at pH 7 and in a Morgan‐Elson assay at pH 3.5. Among the tested compounds, 1, 2, 3, 6, 7, 8, 16, 17 and 18 showed good inhibition of more than 50%, so the IC50 values of these derivatives were determined in the range of 25–41 μm. The IC50 value of the most active hyaluronidase inhibitor Vcpal (6‐palmitoyl‐l‐ascorbic acid) was measured as 8.36 μm. All inhibitors including Vcpal showed twofold less activity at pH 3.5 in a Morgan‐Elson assay. Examination of substituent effects on the activity showed that para‐positions of benzamide needs to be chlorinated or fluorinated to obtain good inhibitory effect. It was found that the introduction of a p‐fluoro benzyl ring in the indole nitrogen has a positive effect for the inhibitory effects of both indole‐2‐ and 3‐carboxamide derivatives.