N-[1-oxo-(optionally 2-aza)-2-alkyl-3-(carboxyl or thiol or hydroxyaminocarbonyl or N-hydroxyformamido)-propyl]-(aryl or heteroaryl)-azacyclo_4-7alkanes or thiazacyclo_4-7alkanes, salts or prodrugs thereof have interesting properties, e.g., in the treatment or prevention of disorders amenable to treatment by PDF inhibitors, such as treatment of bacterial infections.