The present invention provides compounds of formula I wherein R1 is hydrogen, C1-6-alkyl, C1-6-alkyl substituted by fluoro, or C3-6-cycloalkyl; R2 is hydrogen or a substituent selected from the group consisting of —CH2C(═CHR)—COOR, —CH2OCOR, —CH(R)OCOR, —CH(R)OCOOR, —CH(OCOR)OCOR, —CH2COCH2OCOR and R3 is hydrogen or a substituent selected from the group consisting of —CH2C(═CH2)—COOR, —COOCH2C(═CHR)—COOR, —COOCH2OCOR, —COOCH(R)OCOR, —COOCH(R)OCOOR, —COOCH(OCOR)OCOR, —COOCH2COCH2OCOR, and  with the proviso that one of R2 and R3 is hydrogen and the other is not hydrogen, R is hydrogen or C1-6-alkyl; R4 is hydrogen or hydroxy, R5 is hydrogen or &ohgr;-hydroxyalkyl; and X is CH or N, pharmaceutically acceptable salts of the compounds and hydrates of the compounds and of their salts.