Copper(I) Nitrosyls from Reaction of Copper(II) Thiolates with <i>S</i>‑Nitrosothiols: Mechanism of NO Release from RSNOs at Cu

<i>S</i>-nitrosothiols (RSNOs) serve as ready sources of biological nitric oxide activity, especially in conjunction with copper centers. We report a novel pathway for the generation of NO within the coordination sphere of copper model complexes from reaction of copper­(II) thiolates with <i>S</i>-nitrosothiols. Reaction of tris­(pyrazolyl)­borate copper­(II) thiolates ^iPr2TpCu–SR (R = C₆F₅ or CPh₃) with ^tBuSNO leads to formation of ^iPr2TpCu­(NO) and the unsymmetrical disulfide RS–S^tBu. Quantum mechanical investigations with B3LYP-D3/6-311G­(d) suggest formation of a κ¹-N–RSNO adduct ^iPr2TpCu­(SR)­(R′SNO) that precedes release of RSSR′ to deliver ^iPr2TpCu­(NO). This process is reversible; reaction of ^iPr2TpCu­(NO) (but not ^iPr2TpCu­(NCMe)) with C₆F₅S–SC₆F₅ forms ^iPr2TpCu–SC₆F₅. Coupled with the facile, reversible reaction between ^iPr2TpCu­(NO) and C₆F₅SNO to give ^iPr2TpCu–SC₆F₅ and 2 equiv NO, we outline a new, detailed catalytic cycle for NO generation from RSNOs at Cu

Spiroligozymes for Transesterifications: Design and Relationship of Structure to Activity

Transesterification catalysts based on stereochemically defined, modular, functionalized ladder-molecules (named spiroligozymes) were designed, using the “inside-out” design strategy, and mutated synthetically to improve catalysis. A series of stereochemically and regiochemically diverse bifunctional spiroligozymes were first synthesized to identify the best arrangement of a pyridine as a general base catalyst and an alcohol nucleophile to accelerate attack on vinyl trifluoroacetate as an electrophile. The best bifunctional spiroligozyme reacted with vinyl trifluoroacetate to form an acyl-spiroligozyme conjugate 2.7 × 10³-fold faster than the background reaction with a benzyl alcohol. Two trifunctional spiroligozymes were then synthesized that combined a urea with the pyridine and alcohol to act as an oxyanion hole and activate the bound acyl-spiroligozyme intermediate to enable acyl-transfer to methanol. The best trifunctional spiroligozyme carries out multiple turnovers and acts as a transesterification catalyst with <i>k</i>₁/<i>k</i>_uncat of 2.2 × 10³ and <i>k</i>₂/<i>k</i>_uncat of 1.3 × 10². Quantum mechanical calculations identified the four transition states of the catalytic cycle and provided a detailed view of every stage of the transesterification reaction

Computational Design of Enone-Binding Proteins with Catalytic Activity for the Morita–Baylis–Hillman Reaction

The Morita–Baylis–Hillman reaction forms a carbon–carbon bond between the α-carbon of a conjugated carbonyl compound and a carbon electrophile. The reaction mechanism involves Michael addition of a nucleophile catalyst at the carbonyl β-carbon, followed by bond formation with the electrophile and catalyst disassociation to release the product. We used Rosetta to design 48 proteins containing active sites predicted to carry out this mechanism, of which two show catalytic activity by mass spectrometry (MS). Substrate labeling measured by MS and site-directed mutagenesis experiments show that the designed active-site residues are responsible for activity, although rate acceleration over background is modest. To characterize the designed proteins, we developed a fluorescence-based screen for intermediate formation in cell lysates, carried out microsecond molecular dynamics simulations, and solved X-ray crystal structures. These data indicate a partially formed active site and suggest several clear avenues for designing more active catalysts