30 - Kinetics and Selectivity of Strained Cycloalkyne-Based Probes with Sulfenic Acids

Abstract

Protein sulfenic acids are highly reactive intermediates in disulfide formation by biologically relevant reactive oxygen species. Sulfenic acid formation initiates signaling cascades that modulate the function of enzymes and transcription factors. Identifying the site, timing, and conditions of protein sulfenic acid formation remains crucial to understanding cellular redox regulation. Current methods for trapping and analyzing sulfenic acids involve the use of dimedone and other nucleophilic 1, 3-dicarbonyl probes that form covalent adducts with cysteine-derived protein sulfenic acids. As a mechanistic alternative, strained cycloalkynes function effectively as concerted traps of sulfenic acids. We have previously reported that the highly strained bicyclo[6.1.0]nonyne (BCN) reacts with sulfenic acids in proteins and small molecules yielding stable alkenyl sulfoxide products at rates more than 100x greater than 1, 3-dicarbonyl reagents. To better define this class of sulfenic acid traps, we report the reaction kinetics of several commercial and synthetic cycloalkynes, using Fries Acid as a model sulfenic acid, and compare these results to computational models. Further experiments explore the selectivity of these cycloalkynes for sulfenic acids, especially compared to thiols, as well as the ability of these reagents to react with model sulfenamides. The high selectivity and enhanced rate demonstrated by strained alkynes identify them as an emerging class of bioorthogonal probes that complement existing methods for the discovery of sulfenic acid sites and their parent proteins.