18-carbamoyl-3,5,7,9,11,13,15,17-octaoxooctadecanoyl-[OxyC acyl-carrier protein];
The synthesis, in the bacterium Streptomyces rimosus, of the tetracycline antibiotics core skeleton requires a minimal polyketide synthase (PKS) consisting of a ketosynthase (KS), a chain length factor (CLF), and an acyl-carrier protein (ACP). Initiation involves an amide-containing starter unit that becomes the C-2 amide that is present in the tetracycline compounds. Following the initiation, the PKS catalyses the iterative condensation of 8 malonyl-CoA molecules to yield the polyketide backbone of tetracycline. Throughout the proccess, the nascent chain is attached to the OxyC acyl-carrier protein.