Total Synthesis of (+)-12- <i>epi</i> -Fischerindole U Isonitrile and Its Activity as a Substrate of the Halogenase WelO5

Mononuclear nonheme Fe(II) and 2-oxoglutarate-dependent enzymes (Fe(II)/2OG) constitute an enzyme superfamily that oxidizes substrates by activating molecular oxygen (O 2 ) via the highly oxidized iron(IV)-oxo (ferryl) intermediate. Despite the high similarity of their active sites, the enzymes of this superfamily perform a diverse array of reactions such as hydroxylation, halogenation, epoxidation, and desaturation. WelO5, a member of this superfamily, regio- and stereospecifically monochlorinates a free-standing substrate, 12- epi -fischerindole U isonitrile (FIUI), at its aliphatic C(13) to give 12- epi -fischerindole G (FIG). Researchers have proposed that a dynamic reconfiguration of the WelO5 active site governs the selective halogenation of FIUI. Unfortunately, the requirements of spectroscopic and structural methods for large amounts of fully assembled samples of protein–substrate complexes impede the investigation of such reconfiguration. In this work, we describe a synthesis of (+)-FIUI that makes use of the Baran group’s strategy for coupling of indoles with carbonyl compounds. We apply EPR and LC–MS methods to demonstrate the ability of WelO5 to bind the synthetic (+)-FIUI and subsequently convert it to FIG.