1.65 g (11.9 mmol) of potassium carbonate are added at 25° C. under an argon atmosphere to 0.900 g (4.75 mmol) of 3-methoxycarbonyl-5-methyl-1H-indole in 10 cm3 of dimethyl sulphoxide. After stirring at 25° C. for 0.5 hour, 0.677 cm3 (4.75 mmol) of 1-chloroisoquinoline is added. After stirring at 100° C. for 48 hours, the reaction mixture is cooled and diluted with 100 cm3 of ethyl acetate and then washed with 3 times 50 cm3 of water and 25 cm3 of saturated aqueous sodium chloride solution. The organic phase is dried over anhydrous magnesium sulphate, filtered and concentrated to dryness under reduced pressure (2.7 kPa) to give 1.50 g of a residue which is purified by flash chromatography [eluent: cyclohexane/ethyl acetate (8/2 by volume)]. After concentrating the fractions to dryness under reduced pressure (2.7 kPa), 1.4 g of 3-methoxycarbonyl-1-(isoquinol-1-yl)-5-methyl-1H-indole are obtained in the form of a white solid melting at 142° C.
