195 mg 5-(4-aminophenoxy)-4-methoxymethyl-beta-carboline-3-carboxylic acid ethyl ester is suspended in a mixture of 2 ml of water and 2 ml of concentrated hydrochloric acid and, after cooling to 0° C., is mixed drop by drop with a solution of 35 mg of sodium nitrite in 0.5 ml of water. After the addition is completed, it is stirred for 45 minutes at 0° C., whereby a bright yellow solution results. To this is added at 0° C. drop by drop a solution which was previously prepared by addition of 69 mg of sodium sulfate in 0.5 ml of water to 250 mg of copper(II) sulfate, 5 H2O and 87 mg of sodium chloride in 1 ml of water, suctioning off of the precipitate and dissolution in 0.5 ml of concentrated hydrochloric acid. After the addition is completed, a yellow precipitation has occurred and the mixture is then heated to the end of the development of gas on the steam bath. Then it is diluted with water, alkalized with ammonia solution and extracted with ethyl acetate. After evaporation of the organic phase, it is chromatographed over silica gel with methylene chloride: ethanol=10:1 as eluant. 130 mg (55% of theory) of 5-(-4-chlorophenoxy)-4-methoxymethyl-beta-carboline-3-carboxylic acid ethyl ester with a melting point of 207° C. is obtained.
