Vibralactone is isolated from the basidiomycete fungus Boreostereum vibrans as one of the strongest lipase inhibitors. Its unusual beta-lactone-fused bicycle is derived from an aryl ring moiety via an oxidative ring-expansion prior to an intramolecular cyclization. VibC stehr-Sh.112560 performs the carbocycle formation of an oxepinone to a fused bicyclic beta-lactone
