Synthesis, antioxidant and carbonic anhydrase inhibitory properties of monopeptide-anthraquinone conjugates

Abstract: Novel monopeptide-anthraquinone conjugates (1-16) were synthesized by the reaction of appropriate N-protected amino acid with 2-hydroxymethylanthraquinone in good or high yields. The structural elucidation of the new compounds was accomplished by 1H NMR, 13C NMR, MS, FT-IR spectroscopy and elemental analysis techniques. The carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity of the new compounds was determined against two human (h) isoforms, hCA I and hCA II. While three of the sixteen compounds showed moderate in vitro carbonic anhydrase inhibitory properties against hCA II with inhibition constants in the micromolar level (43.5, 67.4 and 78.1 μM), they did not show inhibitory activity against hCA I up to 100 μM concentration. The antioxidant abilities of the compounds were determined using the 1,1-diphenyl-2-picrylhydrazil (DPPH) radical scavenging method, ferric ion reducing assay and metal chelation methods. While a small amount of antioxidant activity was observed according to the DPPH and ferric ion reducing power assay methods, none of the compounds showed antioxidant properties according to the metal chelating activity method at the concentrations studied.