Total synthesis and preliminary SAR study of (±)-merochlorins A and B.

A modular synthesis of merochlorins A and B, two naturally occurring antibiotics, has been achieved concisely from readily available building blocks in 4-6 steps. The key steps include the bio-inspired tandem phenol oxidative dearomatization/[5 + 2] and [3 + 2] cycloadditions to construct the tricyclic cores of the targets, and the intermolecular Diels-Alder reaction followed by dehydrogenative aromatization to assemble the remaining aromatic units. The antibacterial activities of merochlorins A, B and some advanced synthetic intermediates were also evaluated, which provided valuable information on the structure-activity relationship (SAR) of this class of new antibiotics.