Heterologous biosynthesis of amidated polyketides with novel cyclization regioselectivity from oxytetracycline polyketide synthase.

Heterologous expression of the minimal oxytetracycline polyketide synthase and the amidotransferase OxyD in Streptomyces coelicolor strain CH999 afforded two novel amidated polyketides, WJ85 (4) and WJ85b (5). WJ85 is a C-9 unreduced decaketide that is primed by a malonamyl starter unit. WJ85 is cyclized via an unusual C-11 to C-16 intramolecular aldol condensation not observed among known aromatic polyketides. The structures of WJ85 and the previously characterized WJ35 suggest that the presence of an amide starter unit has a profound effect on the cyclization regioselectivity and reactivity of a polyketide backbone. WJ85b is an anthraquinone and is an oxidized product of WJ85.