Chromatographic and electrophoretic behavior of indole-2-carboxylic acids

Electrophoresis

“…Analyses of carboxylic (945), aromatic carboxylic and nitrobenzenesulfonic (445), indole-2-carboxylic (708), and phenylphosphinic and phenylphosphonic (679) acids have been accomplished. Electrophoregrams of polyaminocarboxylic acids can be colored by Folin-Ciocalteau reagent for quantitative measurement (745).…”

Synthesis of Methyl 5- and 6-Nitroindole-2-carboxylates by Nitration of Indoline-2-carboxylic Acid

“…Whereas ethyl 5-nitroindole-2carboxylate was obtained by Fischer indole synthesis from the 4-nitrophenylhydrazone of ethyl pyruvate in 50-60% yields, ethyl 6-nitroindole-2-carboxylate was obtained from the 3-nitrophenylhydrazone of ethyl pyruvate in 8% yield as a mixture with the 4-nitro isomer. [1][2][3] Methyl 4,5,6, and 7-nitroindole-2-carboxylates were also obtained by condensation of the corresponding nitrobenzaldehydes with methyl 2-azidoacetate followed by thermolysis. 4 Nitration of protonated indoline leads selectively to 6-nitroindoline, whereas nitration of 1-acetylindoline produces 1-acetyl-5-nitroindoline as protonated nitrogen gives meta-direction whereas the non-protonated N-acetyl group in indoline shows para-direction.…”

“…Nitration of commercially available indoline-2-carboxylic acid with concentrated HNO 3 in concentrated H 2 SO 4 led to a mixture of 6-and 5-nitroindoline-2-carboxylic acids 2 and 5, in which the 6-nitro derivative 2 was the predominant compound (Scheme). Compound 5 admixed with 2 was extracted with EtOAc at pH < 2, then the aqueous phase was adjusted to pH 4.5-5.0 and extracted with EtOAc, to give 72% of pure 6-nitroindoline-2-carboxylic acid (2), which was esterified to give methyl 6-nitroindoline-2-carboxylate (3). Additional amounts of 3 (6%) and 6 (10%) were obtained after esterification of the products extracted from the reaction mixture at pH < 2, followed by column chromatography.…”