Highly Stereoselective Biocatalytic One-Pot Synthesis of Chiral Saturated Oxygen Heterocycles by Integration of a Biosynthetic Heterocyclase into Multiple-Enzyme Cascades

The secondary metabolism is a rich source of enzymes with new synthetically attractive activities that have not yet been integrated into the toolbox of biocatalysis. Chiral saturated oxygen heterocycles (CSOHs) are abundant structural elements of natural products and other value-added compounds. We present a biocatalytic method for the synthesis of CSOHs from readily accessible precursors that combines an intramolecular oxa-Michael addition (IMOMA)-catalyzing cyclase (CYC) from a biosynthetic pathway with alcohol dehydrogenases (ADHs) and thioester-derivatizing enzymes. The one-pot ADH-CYC reaction enables access to various tetrahydropyran (THP) and tetrahydrofuran thioesters under control of up to four stereocenters. These products are readily convertible into useful CSOH ketone, amide, aldehyde/alcohol, ester, and carboxylic acid building blocks by chemical and enzymatic means. The extendibility to more complex multienzyme cascades was demonstrated by the addition of a thioesterase and a carboxylic acid reductase, allowing the straightforward chemoenzymatic synthesis of the natural product (-)-civet, a new derivative, and a THP alcohol. The integration of IMOMA cyclases into enzymatic cascades allows better exploitation of the high synthetic potential of this new group of ring-forming enzymes and expands the repertoire for the synthesis of pharmacologically relevant CSOHs as a highly selective and versatile alternative. This approach will be adaptable for the synthesis of a wide range of CSOHs by varying ADHs, IMOMA cyclases, and modifying enzymes.