Synthesis and antioxidant activity of a new class of pyrazolyl indoles, thiazolyl pyrazolyl indoles

A new class of bis and tris heterocycles–pyrazolyl indoles and thiazolyl pyrazolyl indoles were prepared from the Michael acceptor (E)-3-(1H-indol-3-yl)-1-arylprop-2-en-1-ones by ultrasound irradiation technique and tested for antioxidant activity. The thiazolyl pyrazolyl indoles and pyrazolyl indoles showed greater radical scavenging activity than pyrazolinyl indoles. Amongst all the tested compounds, 3-(1-(4′′-(p-chlorophenyl)thiazol-2′′-yl)-3′-p-tolyl-1H-pyrazol-5′-yl)-1H-indole (7b) and 3-(1-(4′′-(p-chlorophenyl)thiazol-2′′-yl)-3′-(p-methoxyphenyl)-1H-pyrazol-5′-yl)-1H-indole (7c) displayed promising antioxidant activity when compared with standard drug ascorbic acid. The compounds having electron donating groups (CH3, OCH3) on the phenyl ring exhibited greater antioxidant activity than those with electron withdrawing groups (Cl, Br, NO2).