Compounds of the formula ##STR1## wherein X and X' form C.dbd.O or C.dbd.NOR, R is selected from the group consisting of hydrogen, heterocycle, alkyl, alkenyl, alkynyl, all optionally substituted,or X is ##STR2## R.sub.a and R.sub.b are hydrogen or a hydrocarbon group or form together with the nitrogen a heterocycle, or with A forms a 9-N, 11-O ring, and X' is hydrogen, --Y and Y' have the same definition as X and X', B is hydrogen or OR.sub.4, R.sub.4 is hydrogen or forms together with A a carbonate or a carbamate, A forms with C a double bond or A is OR'.sub.4, R'.sub.4 is hydrogen or forms together with B a carbonate or ##STR3## R.sub.2 is alkyl or --CONH.sub.2, --CONHCOR.sub.11 or --CONHSO.sub.2 R.sub.11, R.sub.11 is a hydrocarbon up to 18 carbon atoms, R.sub.3 is hydrogen, ##STR4## and Z is hydrogen or a carboxylic acid remainder and their non-toxic, pharmaceutically acceptable acid addition salts, their preparation and intermediates useful as antibiotics.