Some electrophilic substitution reactions on 1-substituted-3-acetyl/carbethoxy-5-hydroxy-2-methylindole and the antimicrobial activity of these new indole derivatives

Abstract

Aminomethylation under Mannich reaction conditions on 3-carbethoxy-1-furfuryl-5-hydroxy-2-methylindole <b style="">1</b> and the corresponding bromo derivative <b style="">3</b> occurs regioselectively at C₄ position to furnish the 4-isogramines <b style="">2a-d</b>/<b style="">4a-d</b>. Nitration of 3-carbethoxy/acetyl-1-furfuryl-5-hydroxy-2-methylindoles <b style="">1/8</b> with hydrated ferric nitrate produces 3-carbethoxy/acetyl- 4, 6-dinitro-1-furfuryl-5-hydroxy-2-methylindoles <b style="">6/9</b>. Nitration of 4-isograamine <b style="">2 </b>and bromoindole <b style="">3</b> involves ipso-substitution and furnish the 4, 6-dinitroindole derivative <b style="">6</b> and not the expected 6-nitro-4-isogramine <b style="">5</b>/<b>6</b>-bromo-4-nitroindole <b style="">7</b>. However, nitration of 3.6-diacetylindoles <b style="">18a-d</b> and triacetylindole <b style="">10</b> yields 4-nitroindole derivatives <b style="">19a-d/11</b> wherein the acetyl group remain intact without involving in any ipso-substitution. Acetylation under Friedel-Crafts reaction conditions on 3-acetyl-1-furfuryl-5-hydroxy -2-methylindole <b style="">8</b> occurs at both C₆-position of indole and C₅-position of furan to furnish the triacetylindole <b style="">10</b>. Bromination of <b style="">1</b> with bromine in acetic acid or bromine in dioxane produces only 6-bromoindole <b style="">3</b>. The structures of all these newly synthesised compounds are confirmed by their spectral and analytical data and all these compounds are screened for antimicrobial activity.