Hydrochloric Acid → 3-(6-chloro-1H-indol-3-yl)-2-oxopropanoic acid

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Reaction Steps

To 600 mg of 6-chloro-DL-tryptophan, suspended in 5 ml of methanol, are added, at room temperature, 0,230 ml of triethylamine and the mixture is stirred for approximately 10 minutes. Then, rapidly and under stirring, pyridine-4-carboxyaldehyde (0,240 ml) is added. After approximately 5 minutes, total dissolution of the suspension is obtained. Stirring is continued for 10 minutes. 122 mg of anhydrous ZnCl2 are then added, stirred for 10 minutes, followed by 0,490 ml of 1,8-diazabicyclo-(5,4,0)-undec-7-ene. The solution becomes orange-red in colour. It is left under stirring for approximately 80-90 minutes at room temperature. The limpid red solution is then quickly added dropwise and under rapid stirring to 100 ml of HCl 1N preheated to 50° C. After approximately 10 minutes from completion of the addition a spontaneous precipitation occurs, increasing in time, of a yellowish solid. The mixture is left for a further 20 minutes at 55° C., then for approximately 3 hours it is cooled to room temperature. The abundant precipitate is filtered, washed with acidic water and dried. 195 mg are recovered, with a yield of 54%.

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