N-(3-Oxohexanoyl)-L-homoserine lactone (HSL) (I) is the autoregulator controlling carbapenem antibiotic biosynthesis in Erwinia carotovora ATCC 39048. The chemical synthesis and biological evaluation of analogues of HSL are described. These include alterations of chirality, side-chain modifications, ring size and ring hetero atom. A number of compounds are reported which are capable of restoring the phenotype to a HSL negative mutant but at higher concentrations than HSL. A-factor, the autoregulator of streptomycin biosynthesis in Streptomyces griseus, was not active as an inducer of carbapenem biosynthesis in E. carotovora.