| abstract |
Beta-lactam antibiotics of the formula (I) or a salt thereof are described, wherein R1 represents hydrogen, methoxy or formamido; R2 represents an acyl group; CO2R3 represents a carboxy group or a carboxylate anion, or R3 represents an easily separable carboxy protecting group; L represents -CH =, - (CH2) n where n is 0 or 1, - (CH2) x-Y- (CH2) y- where x and y are independently 0 and 1 and Y represents sulfur or oxygen; R4 represents an optionally substituted gamma- or delta-thiolactone or a lactam ring optionally containing one or (as the case may be) two endocyclic double bonds; and X represents S, SO, SO2, O or CH2. These antibiotics or salts are useful in the treatment of bacterial infections in animals or in humans. |