as shown in reaction scheme 7 compounds of formula XIV, in which Y3 is a suitable leaving group, such as e.g. iodine or bromine, and PG5 stands for a suitable temporary protective group for the carboxyl group, for example tert-butyl, can be deprotected by removal of PG5, and the free carboxylic acid can be then coupled with compounds of formulae H2N???O-PG2 or IIa as described above to give corre