The second part of Step D involves subjecting the mixture obtained in the first part to an ion-exchange resin, preferably Amberlite IRA 400(OH), to obtain the amide compound of formula II. The ion-exchange is conducted in the presence of an inert, organic solvent, preferably a cyclic ether such as tetrahydrofuran, at a temperature of from 10??? to 35??? C. for a period of between 15 and 45 minutes