Biocatalytic Stereodivergent Construction of Axially Chiral Tri- and Tetrasubstituted Allenols via Desymmetric Hydroxylation

Axially chiral allenes serve as versatile building blocks in organic synthesis and are important motifs in natural products. While enantioselective syntheses of disubstituted allenes have been well-established, catalytic construction of trisubstituted and tetrasubstituted allenes with high enantiopurity remains a formidable challenge. In this study, we present a biocatalytic strategy for the stereodivergent synthesis of axially chiral tri- and tetrasubstituted allenols via engineered P450pyr monooxygenase-catalyzed desymmetric hydroxylation of C(sp³)–H bonds. Through structure-guided semirational mutagenesis, enantiocomplementary P450pyr variants were developed to deliver both (R)- and (S)-configured allenols in a highly regio-, chemo-, and enantioselective manner (up to 99% ee). Molecular docking studies elucidated the structural basis for the enhanced and inverted stereocontrol in the engineered mutants, correlating active-site interactions with stereochemical outcomes. This enzymatic platform represents the first example of P450-catalyzed hydroxylation for constructing axially chiral tri- and tetrasubstituted allenes that are otherwise challenging to access.