| abstract |
β-Lactam antibiotics of formula (I) or a salt thereof wherein R1 is hydrogen, methoxy or formamido; R2 is an acyl group; CO¿2R?3 is a carboxy group or a carboxylate anion, or R3 is a readily removable carboxy protecting group; L is -CH=, -(CH¿2?)n where n is 0 or 1, -(CH2)x-Y-(CH2)y- where x and y are independently 0 or 1 and Y is sulphur or oxygen; R?4¿ is an optionally substituted η- or δ-thiolactone or lactam ring optionally containing one or (where applicable) two endocyclic double bonds; and X is S, SO, SO¿2?, O or CH2, useful in the treatment of bacterial infections in humans and animals. |