The free base of N-(3-{(R)-2-[3-(5-amino-indol-1-yl)-1,1-dimethyl-propylamino]-1-hydroxy-ethyl}-phenyl)-benzenesulphonamide-hydrotrifluoroacetate (free base from Example 20; 100 mg, 0.20 mmol) and pyridine (33 μl, 0.41 mmol) are dissolved in 3 ml THF. At 0° C. methyl oxalate chloride (21 μl, 0.22 mmol) is added and the reaction mixture is stirred for 3 hours at RT. The solvent is eliminated in vacuo and the residue is dissolved in 3 ml of methanol. Sodium hydroxide solution (4N; 1.5 ml) is added dropwise to the mixture. Then the reaction mixture is stirred for 18 hours at RT and then acidified with TFA. The solution is chromatographed on Microsorb C18-reverse-phase [acetonitrile (0.1% TFA)/water (0.13% TFA)=10:90→100:0].
