Stereoselective construction of chiral flavanones via enzymatic intramolecular C(sp3)–H activation†

Abstract

Flavanone derivatives utilize the fundamental flavanone framework to enhance and target distinct bioactivities, rendering them valuable precursors in the synthesis and development of pharmaceuticals. Here we explore enzyme-catalyzed intramolecular C(sp³)–H activation of diazo reagents using myoglobin as a catalyst for the preparation of precursors of flavanone compounds. Initial biocatalytic screening indicated that the myoglobin from Physeter catodon displayed observable activity toward the diazo substrate, however with low yield and enantioselectivity. Key residues were identified for site-saturation mutagenesis to tune the protein structural dynamics to enhance the enzymatic properties. Through three rounds of mutation, a triple mutant with a yield of 99% and an enantiomeric excess value of 96% was obtained. Substrate scope studies show that this engineered myoglobin has broad substrate specificity, accepting all 23 diazo analogs as substrates with medium to high yield and enantioselectivity.