with the proviso that when Z is oxygen and X3 is NR13, wherein R13 is hydrogen, alkyl, C1-C4-alkanoyl or aryl, then R6 is other than hydrogen or a substituent at position 2 or 6 of the 6-membered ring A selected from: hydroxyl, C1-C4-alkyloxy, C1-C4-alkyloxycarbonyl, aryloxy and NR9R10;