Rational Design of an Ultrasensitive and Highly Selective Chemodosimeter by a Dual Quenching Mechanism for Cysteine Based on a Facile Michael‐Transcyclization Cascade Reaction

Abstract

Differentiation of biologically important thiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) is still a challenging task. Herein, we present a novel fluorescent chemodosimeter capable of selectively detecting Cys over other biothiols including Hcy and GSH and other amino acids by a facile thiol-Michael addition/transcyclization rearrangement cascade click process. The unique transcyclization step is critical for the selectivity as a result of the kinetically favorable formation of a six-membered ring with the Cys Michael adduct. Moreover, the probe adopts a distinctive dual quenching mechanism-photoinduced electron transfer (PET) and photoinduced intramolecular charge transfer (ICT) to deliver a drastic turn-on fluorescence response only at the Cys-selective transcylization step. The judicious selection of strong electron-withdrawing naphthalimide fluorophore with maleimide group enhances the electrophilicity and thus reactivity for the cascade process leading to fast detection and ultrasensitivity with a detection limit of 2.0 nm (S/N=3). The probe has demonstrated its practical utility potential in Cys imaging in live cells.

The chronological evolution of small organic molecular fluorescent probes for thiols

“…29,32 The corresponding uorescence regulation mechanism was fully illustrated by the Wang group in 2016. 33 Over the past 40 years, other structures such as Ndansylaziridine (4), 34 Acrylodan 835 and 4-oxobut-2-enoate derivatives (9), 36 and a variety of Michael acceptors (squaraine (12), 7oxanorbornadiene, quinone, chromene and nitroolen) were then reported to detect thiols via the one step NAR process. [37][38][39][40] O-phthalaldehyde (OPA, 3) was found to react with both GSH and Hcy in aqueous solutions with appropriate pH conditions eliciting dual channel turn-on uorescent responses and was rst utilized for thiol detection by Cohn and coworkers in 1966.…”

Recent Advances in the Development of Optical Imaging Probes for γ‐Glutamyltranspeptidase

“…The fluorescence of 10 was off initially due to the presence of an electron‐withdrawing succinimide group at the 4‐position of the fluorophore, which could dramatically suppress the ICT process. Upon GGT‐triggered removal of the γ‐Glu group in 10 , a spontaneous transcyclization process, consisting of opening of the succinimide ring and subsequent formation of a thiomorpholinone ring, occurred to afford the transcyclized product ( 10 b ), which showed an increased ICT process relative to that of 10 . Hence, a more than 200‐fold fluorescence increment at λ =473 nm was obtained.…”

“…The fluorescenceof10 was off initially due to the presence of an electron-withdrawing succinimide group at the 4-position of the fluorophore, which could dramatically suppress the ICT process. Upon GGT-triggered removal of the g-Glu group in 10,aspontaneoust ranscyclization process, [23] consisting of opening of the succinimide ring and subsequentf ormation of at hiomorpholinone ring, occurred to afford the transcyclized product (10 b), which showed an in-creasedI CT process relative to that of 10.H ence, am ore than 200-fold fluorescencei ncrement at l = 473 nm was obtained. The detection limit toward GGT was 0.21 mU mL À1 .M oreover, the K m and V max values of 10 were measured to be 17.64 mm and 1.44 mm min À1 ,r espectively;t hese values allow for rapid detection of GGT activity in solution.S ubsequent application in cell imaging revealedt hat GGT-overexpressing OVCAR5c ancer cells could be rapidly lit up by 10,r esulting in bright blue fluorescencet hat could be inhibited by acivicin or Cu 2 + .T he resultingf luorescent product (10 b)d id not contain ar eactive free amine, which might prevent undesired oxidation or modificationsb yo ther endogenous enzymes;t husi mproving the stabilityf or the detection of GGT activity in complex biological samples.…”

A simple two-photon turn-on fluorescent probe for the selective detection of cysteine based on a dual PeT/ICT mechanism

“…It was also tested to determine whether it is a turn-on uorescent probe with high sensitivity and selectivity, which reacts with Cys via a fast two-step thiol-Michael addition and transcyclization cascade reaction. 28 The structure of probe 1 is shown in Fig. 1.…”

“…In addition, uorescent probes with high selectivity for Cys over Hcy are difficult to achieve because they differ by only one methylene group. 28 Recently, we reported that N-(N 0 -butyl-1,8-naphthalimide-4-yl)-maleimide, containing a single maleimide group as the recognition group, is a fast, sensitive, and selective uorescent probe for Cys based on a dual photoinduced electron transfer (PeT) and photo-induced intramolecular charge transfer (ICT) quenching mechanism.…”