Fluorescent Detection of Cysteine Oxidation with a 1H-phenalene-1,3(2H)-dione probe
Manger, Lydia H.
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The amino acid cysteine contains a sulfur atom that is both nucleophilic and redox sensitive. Oxidative modifications of cysteine play important roles in the regulation of many signaling pathways implicated in neurodegeneration, cancer, and aging. Exposure to hydrogen peroxide or other reactive oxygen species oxidizes thiols (R-SH) to sulfenic acid (R-SOH). This oxidative modification is unstable and highly reactive, and it leads to the inactivation of many key enzymes. The goal of the current research is to develop a selective fluorescent reporter to detect cysteine sulfenylation in cells. Cyclohexa-1,3-dione (dimedone) has been shown to selectively react with R-SOH to form a covalent adduct. We set out to elaborate dimedone with the addition of an amino naphthalene ring, an established fluorescent scaffold. Furthermore, we intend to design the probe to respond to conjugation with R-SOH. This is accomplished by mono-fluorination of the alpha position, which prevents deprotonation (pKa ~ 4.3) and enolate formation after conjugation to sulfenic acid. We propose that this will significantly change the resonance properties of the ring system, thus producing a change in fluorescence feature. We anticipate this approach will provide a simple, real-time method for monitoring cysteine oxidation in living cells. Herein we report the synthesis of 1H-phenalene-1,3(2H)-dione from diethyl malonate and 1,8-naphthalic anhydride, a model compound used in the development of the proposed fluorescent sulfenylation probe.