Temporal and spatial resolution of distal protein motions that activate hydrogen tunneling in soybean lipoxygenase.

The enzyme soybean lipoxygenase (SLO) provides a prototype for deep tunneling mechanisms in hydrogen transfer catalysis. This work combines room temperature X-ray studies with extended hydrogen-deuterium exchange experiments to define a catalytically-linked, radiating cone of aliphatic side chains that connects an active site iron center of SLO to the protein-solvent interface. Employing eight variants of SLO that have been appended with a fluorescent probe at the identified surface loop, nanosecond fluorescence Stokes shifts have been measured. We report a remarkable identity of the energies of activation (Ea) for the Stokes shifts decay rates and the millisecond C-H bond cleavage step that is restricted to side chain mutants within an identified thermal network. These findings implicate a direct coupling of distal protein motions surrounding the exposed fluorescent probe to active site motions controlling catalysis. While the role of dynamics in enzyme function has been predominantly attributed to a distributed protein conformational landscape, the presented data implicate a thermally initiated, cooperative protein reorganization that occurs on a timescale faster than nanosecond and represents the enthalpic barrier to the reaction of SLO.

Cooperative Phosphine-Photoredox Catalysis Enables N-H Activation of Azoles for Intermolecular Olefin Hydroamination.

Catalytic intermolecular olefin hydroamination is an enabling synthetic strategy that offers direct and atom-economical access to a variety of nitrogen-containing compounds from abundant feedstocks. However, despite numerous advances in catalyst design and reaction development, hydroamination of N-H azoles with unactivated olefins remains an unsolved problem in synthesis. We report a dual phosphine and photoredox catalytic protocol for the hydroamination of numerous structurally diverse and medicinally relevant N-H azoles with unactivated olefins. Hydroamination proceeds with high anti-Markovnikov regioselectivity and N-site selectivity. The mild conditions and high functional group tolerance of the reaction permit the rapid construction of molecular complexity and late-stage functionalization of bioactive compounds. N-H bond activation is proposed to proceed via polar addition of the N-H azole to a phosphine radical cation, followed by P-N α-scission from a phosphoranyl radical intermediate. Reactivity and N-site selectivity are classified by azole N-H BDFE and nitrogen-centered radical spin density, respectively, which can serve as a useful predictive aid in extending the reaction to unseen azoles.