Enzymatic macrolactonization in the presence of DNA leading to triostin A analogs.

Excised thioesterase domains are versatile catalysts for macrocyclization. However, thioesterase-catalyzed cyclization is often precluded due to the occurrence of hydrolysis and product inhibition. To circumvent these obstacles, we devised an unprecedented strategy: coincubation with DNA to capture the cyclic products possessing DNA-binding properties. In experiments involving echinomycin thioesterase-catalyzed macrolactonization leading to the cyclic triostin A analog TANDEM, we found that the addition of DNA drastically improved the yield of TANDEM (19% --> 67%), with a complete reversal of the cyclization:hydrolysis ratio (1:2 --> 18:1). Furthermore, the applicability of this protocol was demonstrated for a variety of substrates. The results described herein provide insight into the mechanism of echinomycin thioesterase-catalyzed conversions and also pave the way for chemoenzymatic synthesis of the quinoxaline antibiotics and their analogs.