Brønsted acidic ionic liquids: Green, efficient and reusable catalyst for synthesis of fluorinated spiro [indole-thiazinones/thiazolidinones] as antihistamic agents

Brønsted acidic ionic liquid containing nitrogen-based organic cations 1-methylimidazolium and 1-butyl-3-methylimidazolium and inorganic anions such as BF4−, PF6− and PTSA− used as catalysts and reaction medium for synthesis of fluorinated spiro[3H-indole-3,2′-tetrahydro-1,3-thiazine]-2,4′(1H)-diones (4a-f), fluorinated spiro[3H-indole-3,2′-thiazolidine]-2,4′ (1H)-diones (5a-f) in 90–97% yield by one-pot environmentally benign microwave induced technique. Synthesized compounds have been evaluated for their ability to inhibit the contractions induced by histamine on guinea pig ileum. The measurement of pA2 values suggested that the reported compounds showed H1-antagonism.

Graphical abstract. Brønsted acidic ionic liquid containing nitrogen-based organic cations 1-methylimidazolium and 1-butyl-3-methylimidazolium and inorganic anions such as BF4−, PF6− and PTSA− have been used as a catalysts and reaction medium for synthesis of fluorinated spiro[3H-indole-3,2′-tetrahydro-1,3-thiazine]-2,4′(1H)-diones (4) spiro[3H-indole-3,2′-thiazolidine]-2,4′ (1H)-diones (5). The titled compounds are screened for antihistamic activity against guinea pig ileum.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Fluorinated spiro indole thiaza heterocycles synthesized using Brønsted acidic ILs. ► Role of Brønsted acidic ionic liquid with different inorganic anions also studied. ► Titled compounds screened for antihistamic activity. ► Measurement of pA2 values suggested that compounds showed H1-antagonism.