Involved in the biosynthesis of aklavinone which is an important precursor common to the formation of the clinically significant anthracyclines such as carminomycin, daunorubicin (daunomycin), rhodomycin, aclacinomycin T (aklavin) and aclacinomycin A (aclarubicin). These compounds are aromatic polyketide antibiotics that exhibit high cytotoxicity and are widely applied in the chemotherapy of a variety of cancers. Catalyzes the cyclization of aklanonic acid methyl ester to yield aklaviketone. It is also able to use nogalonic acid methyl ester as substrate, but produces exclusively auraviketone with C9-R stereochemistry. methyl aklanonate = aklaviketone kcat is 1 sec(-1) for cyclization with nogalonic acid methyl ester. Optimum pH is 7.2. Antibiotic biosynthesis; daunorubicin biosynthesis. Antibiotic biosynthesis; carminomycin biosynthesis. Antibiotic biosynthesis; rhodomycin biosynthesis. Antibiotic biosynthesis; aclacinomycin biosynthesis. Homotetramer. Belongs to the polyketide cyclase DnrD family.