Synthesis
Methyl 9H-carbazole-3-carboxylate (Compound 18, 818 mg, 3.63 mmol) was added potassium hydroxide (3 g, 53.47 mmol) to a solvent mixture of ethanol (40 mL) and water (10 mL) under stirring. The reaction mixture was stirred under reflux conditions for 16 h and subsequently cooled to room temperature. The solvent was removed by evaporation under reduced pressure and the residue was diluted with deionized water. The mixture was placed in an ice-water bath and the pH was adjusted slowly and dropwise by adding 1 M aqueous HCl to about 2. The precipitated product was extracted with ethyl acetate, washed with brine at acidic pH and dried with MgSO4. After evaporation of the solvent under reduced pressure, the residue was purified by silica gel column chromatography using a heptane solution of 70% ethyl acetate as eluent to afford the title compound 9H-carbazole-3-carboxylic acid (Compound 19) as a beige solid. Yield: 737 mg (96%); Melting point: 271-272°C.
References
[1] Patent: US2012/39804, 2012, A1. Location in patent: Page/Page column 17
[2] European Journal of Medicinal Chemistry, 2013, vol. 69, p. 881 - 907
[3] Patent: US2009/239810, 2009, A1. Location in patent: Page/Page column 80
[4] Patent: US2010/160323, 2010, A1. Location in patent: Page/Page column 37
[5] Phytochemistry (Elsevier), 1991, vol. 30, # 1, p. 343 - 346
