Controlled coupling of aminoglycoside antibiotics to proteins for use in homogeneous enzyme immunoassays

Selective N-acylation of aminoglycoside antibiotics with the N-hydroxysuccinimide ester of methyldithioacetic acid, followed by reaction with methanethiol or dithioerythritol, gives sulfhydryl labeled antibiotics. Alternatively, the nucleophilic sulfhydryl group is incorporated into an antibiotic by treatment with N-acetyl-d,l-homocysteine thiolactone. These derivatives couple readily with proteins that have previously been modified with bromoacetylglycyl groups to provide conjugates for use in the development of homogeneous enzyme immunoassays.