| abstract |
Tetracyclic antibiotics and processes for their preparation β-Lactam antibiotics of the formula I, and their pharmaceutically tolerable salts ##STR1## where X is (CH 2 ) 0-2 , CR(a)R(b), O, SO 0-2 or NR(c), n R1, R2 and R3 are a multiplicity of substituents, are outstanding antibiotics with remarkably good antibacterial activity both against gram-positive and against gram-negative microorganisms. They have a high stability to renal dehydropeptidase. n They are obtained by cyclization of the compounds II ##STR2## or III ##STR3## |