Selective Synthesis of Divergolide I.

Divergolide I (1) is a naphthoquinone ansamycin that exhibits broad antibacterial activity. Its tetracyclic ring system is believed to be biosynthetically assembled via ring contraction of a macrocyclic precursor (proto-divergolide) that is both a macrolactone and a macrolactam. We here report a convergent and enantioselective synthesis that delivers the target molecule in less than 20 linear steps. Our work establishes the absolute configuration of divergolide I, confirms its relative configuration, and demonstrates that the biomimetic cyclization of a proto-divergolide can be surprisingly selective.