Using Ketoreductases for the Chemoenzymatic Synthesis of a Stereotriad

Abstract

Polyketides are diverse natural products of high biological activity produced from complex molecular assembly lines called polyketide synthases (PKSs). Some of the most important bioactive molecules are polyketides, including geldanamycin, doxycycline, tetracycline, and erythromycin. Other polyketides have been shown to have antifungal, antiparasitic, immunosuppressive, and even anticancer properties. Of particular focus here is the ketoreductase (KR), one of the many possible domains within PKSs. The KR reduces carbonyl groups stereoselectively and controls the majority of stereocenters in the polyketide product. KRs have been used in a bottom‐up approach here, harnessing their stereoselective reductions to produce products that would traditionally be difficult and time‐consuming to synthesize. A diketide was first synthesized chemically and reduced with a tylosin KR from Streptomyces fradiae (TylKR2). This reduced diketide was then extended into a triketide through the Masamune C‐acylation reaction. Finally, TylKR2 and a mycolactone KR from a bacterial artificial chromosome (MycKR6) were found to reduce S‐(2‐acetamidoethyl)(4R,5R)‐5‐methoxy‐4‐methyl‐3‐oxoheptanethioate to S‐(2‐acetamidoethyl) (3S,4S,5R)‐3‐hydroxy‐5‐methoxy‐4‐methylheptanethioate in the case of TylKR2 and to S‐(2‐acetamidoethyl) (3R,4S,5R)‐3‐hydroxy‐5‐methoxy‐4‐methylheptanethioate in the case of MycKR6. The reductions were performed in vitro using the glucose dehydrogenase regeneration system with NADP+. In this way, each of the 3 stereocenters was set chemoenzymatically using KRs to form a stereotriad. With similar KRs, it is likely that all 8 possible stereoisomers could be synthesized. Ultimately, these di‐ and triketide building blocks could be extremely useful functional groups to experiment with in drug synthesis and may result in more potent or effective medicines. Additionally, this work could be extended into a methodology for setting as many stereocenters as desired ‐ possibly one day allowing for customizable polyketide synthesis in the same way oligonucleotides and polypeptides can be made today.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.