Kinetic Study on the Reactivity of Azanone (HNO) toward Cyclic C-Nucleophiles

Abstract

Azanone (HNO) is an elusive electrophilic reactive nitrogen species of growing pharmacological and biological significance. Here, we present a comparative kinetic study of HNO reactivity toward selected cyclic C-nucleophiles under aqueous conditions at pH 7.4. We applied the competition kinetics method, which is based on the use of a fluorescein-derived boronate probe FlBA and two parallel HNO reactions: with the studied scavenger or with O2 (k = 1.8 × 104 M−1s−1). We determined the second-order rate constants of HNO reactions with 13 structurally diverse C-nucleophiles (k = 33–20,000 M−1s−1). The results show that the reactivity of HNO toward C-nucleophiles depends strongly on the structure of the scavenger. The data are supported with quantum mechanical calculations. A comprehensive discussion of the HNO reaction with C-nucleophiles is provided.

Boronate-Based Oxidant-Responsive Derivatives of Acetaminophen as Proinhibitors of Myeloperoxidase

“…The fluorescence intensity was followed with a Varioscan LUX plate reader using λ ex = 490 nm, λ em = 515 nm, and slit widths of 12 nm. Using the concentration ratios of fluorescein (product of oxidation of FLBA), [FL] 0 /[FL], where [FL] 0 is the yield of fluorescein in the absence of the acetaminophen derivative, and the previously reported rate constants for the FLBA reactions with ONOO – ( 2 k = 1.0 × 10 6 M –1 s –1 ) and HOCl ( 2 k = 1.11 × 10 4 M –1 s –1 ), the rate constants for the reaction of AMBB and AAPBA with both oxidants were calculated according to eq . FLBA + oxidant → k FLBA + oxidant Fluorescein 0.25em ( FL ) + normalB false( OH false) 3 normalR ‐ normalB false( OH false) 2 + oxidant → k normalR ‐ normalB false( OH false) 2 + oxidant normalR ‐ OH + normalB false( OH false) 3 false[ FL false] 0 false[ FL false] − 1 = k normalR ‐ normalB false( OH false) 2 + oxidant k FLBA + oxidant × false[ normalR ‐ normalB false( OH false) 2 false] false[…”

“…The rate constants of the reactions of AMBB and AAPBA with ONOO – and HOCl were determined by a competition kinetic method using FLBA as a reference compound. ,, In this approach, two pseudo-first-order reactions were assumed, a reaction between FLBA and the selected oxidant, ONOO – or HOCl (eq ), and between the investigated acetaminophen derivative (R-B­(OH) 2 ) and the oxidant (eq ). Typically, the set of samples containing FLBA (20 μM), phosphate buffer (50 mM, pH 7.4), and AMBB or AAPBA (0–160 μM) in Eppendorf tubes was prepared.…”

Activatable NIR-II organic fluorescent probes for bioimaging

“…Overproduction of ONOO - would induce oxidative injury linked with a large number of diseases 75 , 76 . The sensing strategies of ONOO - -activatable probes include the production of amido from dearylation reaction (probe 14), deboronation (probe 15), oxidation of unsaturated bond (probe 16), and decomposition of α-ketoamide group (probe 17) and so on 77 - 80 . NO can serve as an oxidative stress biomarker for diseases involving oxidative injury.…”

The Chemistry of HNO: Mechanisms and Reaction Kinetics

“…The use of boronate fluorogenic/colorimetric probes, in combination with a competition kinetics approach was proposed as a novel approach to study the kinetics of HNO reactions ( Smulik et al, 2014 ). Over the last 7 years, the usefulness of this methodology was demonstrated in the studies of HNO reactivity toward a number of its scavengers ( Smulik et al, 2014 ; Smulik-Izydorczyk et al, 2017 ; Smulik-Izydorczyk et al, 2019 ; Artelska et al, 2021 ; Smulik-Izydorczyk et al, 2021 ). The principle of this method is based on the competition between O 2 and the scavenger of interest for their reaction with HNO released from Angeli’s salt or other HNO donor.…”

“…Recently, it was shown that C -nucleophiles can act as efficient scavengers of HNO ( Artelska et al, 2021 ). There was a strong dependence of the reactivity of C -nucleophiles toward HNO on nucleophile structure ( Figure 1 ), while due to the low p K a values all those nucleophiles are present in the solution in their deprotonated, anionic forms in aqueous solution at pH 7.4.…”