Synthesis of new spiroindolinones incorporating a benzothiazole moiety as antioxidant agents

3H-Spiro[1,3-benzothiazole-2,3′-indol]-2′(1′H)-ones 3a–c and 4a–e were synthesized from treating the 5-substituted 1H-indole-2,3-diones with 2-aminothiophenol in ethanol. The structures were confirmed by elemental analyses, spectrometry (IR, 1H NMR, 13C NMR, HSQC-2D and LCMS-APCI) and single crystal X-ray analysis. The new compounds were screened for their antioxidant activities such as the Fe3+/ascorbate system induced inhibition of lipid peroxidation (LP) in liposomes, trolox equivalent antioxidant capacity (TEAC), scavenging effect on diphenylpicryl hydrazine (DPPH), and reducing power. These compounds showed potent scavenging activities against DPPH and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS+) radicals, reducing powers, and strong inhibitory capacity on lipid peroxidation. Compound 4a incorporating methyl both at R1 and R2 was found to be the most potent antioxidant described in this study. Compounds 3b and 4b were selected as representative compounds by the National Cancer Institute for screening against anticancer activity and these compounds were found to be cytotoxic against CNS cancer cell line SNB-75 in the primary screen.

Graphical abstractNew series of 3H-Spiro[1,3-benzothiazole-2,3′-indol]-2′(1′H)-ones showed potent scavenging activities against DPPH and ABTS+ radicals, reducing powers, and strong inhibitory capacity on lipid peroxidation. Most compounds displayed very good antioxidant activity.Figure optionsDownload full-size imageDownload as PowerPoint slide