| abstract |
ABSTRACT Tetracyclic antibiotics and processes for their prepara-tion .beta.-Lactam antibiotics of the formula I, and their pharma-ceutically tolerable salts I where X is (CH2)0-2, CR(a)R(b), O, SO0-2 or NR(c), R(1), R(2) and R(3) are a multiplicity of substituents, are outstanding antibiotics with remarkably good anti-bacterial activity both against gram-positive and against gram-negative microorganisms. They have a high stability to renal dehydropeptidase. They are obtained by cyclization of the compounds II II or III III |