1.84 g of the compound of Example 1, 1.8 g of N-tritylimidazole-4-carboxylic acid, 1.92 ml of diisopropylethylamine and 1.76 g of O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate are stirred at ambient temperature for 24 hours. After dilution with 500 ml of water, filtration, and extraction with dichloromethane, the organic phases are dried and filtered and then concentrated under reduced pressure. Crystallisation of the residue in an ethanol-diethyl ether-hydrogen chloride mixture enables the expected compound to be isolated.
