Aromatic polyketides are an important class of natural products with various bioactivities, and their structural diversity arises from modifications to their aromatic frameworks. In this study, we identify a stereoselective aromatase/cyclase (ARO/CYC) FasU, which is responsible for forming the axial chiral biphenyl framework in fasamycin. FasU catalyzes sequential decarboxylation and cyclization/aromatization with strict