6052-68-2

50-00-0

73-22-3

6052-68-2

The general procedure for the synthesis of 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid from formaldehyde and L-tryptophan was as follows: first, 1-propanesulfonic acid (817 mg, 4 mmol) was mixed with 2.5 M NaOH solution (1.6 mL), and the mixture was stirred at room temperature until it became clear. Subsequently, 37% formalin (4.87 mL) was added to the mixture. The reaction mixture was stirred at room temperature for 2 hours and then refluxed for 3 hours. Upon completion of the reaction, it was neutralized with 2 M HCl solution to pH 5. The precipitate precipitated was filtered, washed sequentially with water and methanol and finally dried under vacuum to afford the target product 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid. The yield of this step was 99% and the product was a colorless solid with a melting point of 302.2-304.6 °C. Mass spectrometry (FAB) analysis showed m/z 217 (M+1, 100%).