收藏切换
Thiophosphoryl pyridinol/pyrimidinol-based probes for covalent and fluorescent sensing of intracellular Cu2+
收藏切换
PDF
Zhiyuan Qia, Jing Chena, Wenhao Xiea, Zhibei Qua, Motonari Uesugia, b, Lu Zhoua, c
Chinese Chemical Letters | 2026, 37(9) : 111924
Less
收藏切换
Chinese Chemical Letters | 2026, 37(9): 111924
• Communication •
Thiophosphoryl pyridinol/pyrimidinol-based probes for covalent and fluorescent sensing of intracellular Cu2+
Full
Zhiyuan Qia, Jing Chena, Wenhao Xiea, Zhibei Qua, Motonari Uesugia, b, Lu Zhoua, c
Affiliations
  • aSchool of Pharmacy, Fudan University, Shanghai 201203, China
  • bInstitute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
  • cQuzhou Fudan Institute, Quzhou 324002, China
About Author:

1 These authors contributed equally to this work.

CRediT authorship contribution statement

Zhiyuan Qi: Writing – review & editing, Writing – original draft, Validation, Methodology, Investigation, Formal analysis, Data curation.

Jing Chen: Methodology, Investigation, Formal analysis, Data curation.

Wenhao Xie: Writing – review & editing, Data curation.

Zhibei Qu: Supervision, Formal analysis.

Motonari Uesugi: Writing – review & editing, Writing – original draft, Supervision, Project administration, Formal analysis.

Lu Zhou: Writing – review & editing, Writing – original draft, Supervision, Resources, Project administration, Funding acquisition, Formal analysis, Conceptualization.

Published: 2026-09-15 doi: 10.1016/j.cclet.2025.111924
Outline
收藏切换

Copper (Cu) is essential for life, with its redox cycling (Cu+/Cu2+) underpinning key biological processes. Although significant progress has been made in developing fluorescent probes for Cu+, reliable tools for detecting intracellular Cu2+ remain limited, leaving a critical gap in the bioinorganic chemistry toolkit. To address this need, we developed an activity-based sensing (ABS) strategy for live-cell Cu2+ detection that leverages Cu2+-dependent bioorthogonal conjugation. Specifically, we engineered thiophosphoryl pyridinol/pyrimidinol dyes that undergo Cu2+-mediated activation, enabling covalent labeling of proximal proteins within intracellular Cu2+-enriched microdomains and concomitant turn-on fluorescence. This work not only offers a powerful tool for detecting intracellular Cu2+ fluctuations under exogenous stimuli but also proposes thiophosphorylated pyridinol/pyrimidinol scaffolds as a versatile platform for future intracellular Cu2+ sensing applications.

Thiophosphorylated pyridinol/pyrimidinol  /  Activity-based sensing  /  Intracellular Cu2+  /  Probes  /  Fluorescence imaging
Zhiyuan Qi, Jing Chen, Wenhao Xie, Zhibei Qu, Motonari Uesugi, Lu Zhou. Thiophosphoryl pyridinol/pyrimidinol-based probes for covalent and fluorescent sensing of intracellular Cu2+[J]. Chinese Chemical Letters, 2026 , 37 (9) : 111924 - . DOI: 10.1016/j.cclet.2025.111924
Copper ions are essential metal ions for life [1–3]. Through redox cycling between monovalent copper (Cu+) and divalent copper (Cu2+), they play catalytic roles in critical biological processes such as metabolism, proliferation, growth, and respiration [2,4–11]. Concurrently, clinical studies have demonstrated that dysregulation of copper-dependent redox activity is closely associated with pathological conditions including cancer [7], inflammatory immune responses [12,13], major neurodegenerative diseases [14], and hereditary disorders of copper metabolism [15,16]. Owing to the intracellular reducing environment, Cu+ predominates over Cu2+ within cells [17]. Consequently, fluorescence-based detection techniques targeting Cu+ have achieved significant advancements [18–27]. In contrast, Cu2+ exists at lower concentrations in living cells [17]. Additionally, Cu2+ exhibits paramagnetic properties, enabling strong fluorescence signal quenching through electron or energy transfer pathways [28,29]. Consequently, most Cu2+-responsive probes operate via turn-off mechanisms [28,29]. That severely limited the visualization of Cu2+ and created substantial obstacles for investigating intracellular Cu2+ distribution, coordination interactions with proteins, and its correlations with various pathological factors.
Driven by the discovery of metal ion-mediated covalent modification of proteins by small molecules, chemists have developed activity-based sensing (ABS) strategies to address the pressing need for detecting intracellular metal ions and their responses to exogenous/endogenous stimuli [17,30,31]. These approaches leverage metal ion-triggered covalent reactions to achieve the spatial anchoring of probes through conjugation with proteins proximal to metal ion sites [17,30,31]. By leveraging Cu+/Cu2+-directed acyl imidazole strategies, scientists developed probes CD649 and CD649.2 for intracellular labile copper pools (Fig. 1) [17,30]. Upon Cu+/Cu2+coordination, the probes trigger Lewis acid activation of the acyl imidazole moiety, enabling covalent capture of proximal protein nucleophilic residues [30]. This mechanism allows for the spatial retention of the fluorophore while liberating fluorescence-quenching Cu2+ ions [17]. Therefore, this approach enables the real-time tracking of dynamic fluctuations in intracellular labile copper pools [17]. Notably, the CD649.2 exhibited dual selectivity for copper ions and the divalent oxidation state [17].
Although progress has been made in ABS-based copper ion probes, current strategies predominantly employ the acyl imidazole core framework, with a notable absence of alternative usable core structures. To address this limitation and explore alternative structural frameworks, we have developed a Cu2+-directed covalent labeling strategy by using thiophosphoryl pyridinol/pyrimidinol as a reactive and dual Cu2+-recognizing group. It reacts with nucleophilic lysine under alkaline conditions [32]. Both sulfur atom of thiophosphoryl and pyridine/pyrimidine rings are widely recognized as potent Cu2+ chelators and have been extensively utilized in probe design [33–35]. Coordination to the Lewis acidic Cu2+ center enhances the electrophilicity of the thiophosphoryl moiety, thereby inducing covalent conjugation with proteins (Fig. 1). This mechanism enables detection of Cu2+ fluctuations in labile copper pools within living cells under exogenous stimuli.
To develop Cu2+-responsive ABS probes capable of proximal protein labeling, we designed target compounds Q1–Q5 featuring a coumarin fluorophore, a diethylene glycol spacer, and thiophosphoryl pyridinol/pyrimidinol that integrate covalent anchoring and Cu2+-coordination functionalities. The designed compounds were successfully synthesized via a two-step reaction routine (Fig. 2).
Next, we compared the activity of Q1–Q5 under Cu2+-catalyzed conditions. Sodium dodecyl sulfate polyacrylamide gel electrophoresis| (SDS-PAGE) fluorescence imaging showed that compounds with ortho-positioned nitrogen (Q3, Q4 and Q5) exhibited activity, whereas those lacking ortho-nitrogen (Q1, Q2) showed negligible activity (Fig. 3A). Furthermore, introduction of additional nitrogen atoms at either the ortho (Q4) or para position (Q5) enhanced activity compared to Q3 (Fig. 3A). Comparative analysis of Q3 and Q3a revealed that replacing the sulfur atom with an oxygen atom (Q3a) abolished the Cu2+-catalyzed enhancement of labeling activity (Fig. 3B). These results demonstrated the critical importance of the ortho-positioned nitrogen atoms and sulfur atom.
To evaluate the Cu2+ selectivity of Q3–Q5, we performed fluorescent labeling assays using HeLa cell lysate as a proteomic substrate in vitro. The lysate was pre-incubated with various metal ions (250 µmol/L each) under physiological buffer conditions (50 mmol/L HEPES, pH 7.4) for 30 min. For the Fe2+ and Cu+ conditions, tris(2-carboxyethyl)phosphine (TCEP, 1000 µmol/L) was included as a reducing agent. Following the metal ion pretreatment, the samples were incubated with Q3–Q5 (50 µmol/L) for 2 h at 20 ℃. As shown in Fig. S1 (Supporting information), subsequent fluorescent scanning analysis of SDS-PAGE separated samples demonstrated that Q3 (Fig. S1A), Q4 (Fig. S1B), and Q5 (Fig. 3C) exhibited Cu2+-dependent covalent labeling of lysate proteins, with significantly higher efficiency than observed for other metal ions. Notably, even under conditions where Cu+ concentration is tenfold higher than that of Cu2+, Q5 remains inactive (Fig. S2 in Supporting information), demonstrating its high selectivity for Cu2+.
Next, we examined the effects of various conditions on Cu2+-dependent covalent labeling of proteins, including Cu2+ concentration and reaction time, as well as pH value and competition with copper chelators. As shown in Figs. S3 and S4 (Supporting information), the protein labeling of Q5, catalyzed by Cu2+ ions, exhibits dependence on Cu2+ concentration and reaction time, aligning well with the intended design (Figs. S3A and B). Further experimental results indicate that Q5 labels proteins more readily under alkaline conditions (Fig. S3C). Additionally, Cu2+ chelator tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl] amine (TBTA, Fig. S4B) inhibits the Cu2+-dependent protein labeling of Q5 in a concentration-dependent manner (Fig. S4A).
To delineate the underlying mechanism, we first evaluated the effect of Cu2+ on the hydrolytic activity of thiophosphoryl pyrimidinol. To circumvent potential interference from the coumarin moiety, we modified the Q5 by replacing the coumarin group with a butynyl group, yielding the redesigned compound R5 (Fig. 4A). Hydrolysis kinetics of R5 (1 µmol/L) were subsequently analyzed in HEPES buffer (pH 8.0). High performance liquid chromatography (HPLC) monitoring revealed slow hydrolysis of R5 under a mild alkaline condition, with ~30% degradation observed within 92 min (Fig. 4B). Notably, Cu2+ (5 µmol/L) dramatically accelerated this process, as evidenced by detectable hydrolysis within 2 min and complete degradation within 92 min (Fig. 4B). Liquid chromatography-mass spectrometry (LC-MS) analysis identified two hydrolysis products: pyrimidinol (m/z 97.0401 [M + H]+, Fig. 4C) eluting at 2.9 min (Fig. S5 in Supporting information), and a thiophosphate intermediate (m/z 243.0028 [M − H]−, Fig. 4D) eluting at 5.9 min (Fig. S5), corresponding to the hydrolysis of the thiophosphoryl pyrimidinol fragment. These results suggest that Cu2+ promotes the hydrolytic activation of the thiophosphoryl pyrimidinol unit, thereby potentiating the compounds’ covalent protein-labeling activity.
Lysine is highly nucleophilic and predominantly located on protein surfaces, making it an accessible target for covalent reagents and probes [31,36,37]. To examine Cu2+-dependent lysine modification by R5, we conducted LC-MS analyses of R5 (5 µmol/L) and Cbz-Lys (0.5 µmol/L, Fig. 4A) reaction in the presence of Cu2+ (25 µmol/L) (Fig. S6A in Supporting information). The product detected (m/z 519.1982 [M − H]−, Fig. 4E) was confirmed as R5K (a thiophosphorylated lysine adduct) by comparison with a synthetic standard (Fig. S7 in Supporting information). Critically, no R5K formation was observed under Cu2+-free conditions, even after 12 h of incubation during which R5 had fully been hydrolyzed (Fig. S6B in Supporting information). Collectively, these mechanistic studies demonstrate that Cu2+ binding enhances the reactivity of the thiophosphorylated pyrimidinol moiety, promoting either hydrolysis or lysine conjugation (Fig. 4A).
Building on the Cu2+ selectivity of the compounds, we further investigated their ability to detect changes in intracellular Cu2+ levels. Among the tested compounds, Q5 exhibited the highest Cu2+-catalyzed activity in vitro (Fig. 3A). As shown in Figs. S8 and S9 (Supporting information), further cellular experiments and stability assays confirmed the low cytotoxicity of Q5 toward HeLa cells (50% cytotoxic concentration (CC50) = 75 ± 0.41 µmol/L, Fig. S8) and its slow hydrolysis under physiological conditions (phosphate buffered saline (PBS), pH 7.4, 37 ℃, Fig. S9). These results prompting the selection of Q5 for monitoring intracellular Cu2+ fluctuations. To validate its responsiveness, intracellular Cu2+ levels were modulated by pre-incubation with Cu(gtsm) (2 µmol/L) (a membrane-permeable Cu2+ ionophore, Fig. S10 in Supporting information) to elevate Cu2+ pools or treatment with TETA (100 µmol/L) (triethylenetetramine, a high-affinity Cu2+ chelator, Fig. S10) to deplete endogenous Cu2+, followed by incubation with Q5 (1 µmol/L). Live-cell fluorescence imaging revealed distinct Cu2+-dependent responses. Cu(gtsm)-treated cells showed markedly enhanced fluorescence compared to untreated control (Figs. 5A and B). TETA-treated cells exhibited significant fluorescence attenuation (Figs. 5A and B). The trend that cellular fluorescence intensity changes of Q5 is similar to that of the Cu2+ probe N-aminofluorescein (Fig. S11 in Supporting information) [38–40]. These results conclusively demonstrate that Q5 serves as a reliable probe for monitoring the changes of labile Cu2+ levels in living cells. Subcellular co-localization experiments demonstrated that Q5 localizes to endoplasmic reticulum, lysosomes, and mitochondria (Fig. S12 in Supporting information).
In summary, we have successfully developed a novel class of Cu2+-dependent probes based on activity-driven labeling by thiophosphoryl pyridinol/pyrimidinol. Fluorescence labeling assays in cell lysates demonstrated the high selectivity of compounds for Cu2+. Mechanistic studies revealed that Cu2+ enhances the hydrolytic activation of the thiophosphoryl pyrimidinol, which catalyzes compounds to react with lysine residues, thereby enhancing protein-targeted labeling efficacy. Intracellular fluorescence imaging experiments demonstrated that Q5 enables the detection of Cu2+ fluctuations in living cells under exogenous stimuli. This study provided the thiophosphoryl pyridinol/pyrimidinol as a functional group for detecting labile Cu2+ levels in live cells, laying a solid foundation for the broader application of such chemotypes in chemical biology.
1
S.M. Adam, G.B. Wijeratne, P.J. Rogler, et al., Chem. Rev. 118 (2018) 10840–11022.
2
A.V. Davis, T.V. O’Halloran, Nat. Chem. Biol. 4 (2008) 148–151.
3
E.L. Que, D.W. Domaille, C.J. Chang, Chem. Rev. 108 (2008) 1517–1549.
4
C.M. Ackerman, C.J. Chang, J. Biol. Chem. 293 (2018) 4628–4635.
5
C.J. Chang, Nat. Chem. Biol. 11 (2015) 744–747.
6
L. Chen, J. Min, F. Wang, Signal Transduct. Target. Ther. 7 (2022) 378.
7
E.J. Ge, A.I. Bush, A. Casini, et al., Nat. Rev. Cancer 22 (2022) 102–113.
8
F.P. Guengerich, J. Biol. Chem. 293 (2018) 4603–4605.
9
K.M. Lancaster, S. DeBeer George, K. Yokoyama, et al., Nat. Chem. 1 (2009) 711–715.
10
M.L. Schlief, A.M. Craig, J.D. Gitlin, J. Neurosci. 25 (2005) 239–246.
11
L. Zhao, J. Li, G. Chen, et al., Chin. Chem. Lett. 37 (2026) 110959.
12
E.W. Hunsaker, K.J. Franz, Inorg. Chem. 58 (2019) 13528–13545.
13
C. White, J. Lee, T. Kambe, et al., J. Biol. Chem. 284 (2009) 33949–33956.
14
K.J. Barnham, A.I. Bush, Chem. Soc. Rev. 43 (2014) 6727–6749.
15
S.G. Kaler, Nat. Rev. Neurol. 7 (2011) 15–29.
16
S. Lutsenko, Biochem. Soc. Trans. 36 (2008) 1233–1238.
17
A.T. Pezacki, C.D. Matier, X. Gu, et al., Proc. Natl. Acad. Sci. U. S. A. 119 (2022) e2202736119.
18
C.M. Ackerman, S. Lee, C.J. Chang, Anal. Chem. 89 (2017) 22–41.
19
S.C. Dodani, D.W. Domaille, C.I. Nam, et al., Proc. Natl. Acad. Sci. U. S. A. 108 (2011) 5980–5985.
20
S.C. Dodani, A. Firl, J. Chan, et al., Proc. Natl. Acad. Sci. U. S. A. 111 (2014) 16280–16285.
21
D.W. Domaille, E.L. Que, C.J. Chang, Nat. Chem. Biol. 4 (2008) 168–175.
22
D.W. Domaille, L. Zeng, C.J. Chang, J. Am. Chem. Soc. 132 (2010) 1194–1195.
23
T. Hirayama, G.C. Van de Bittner, L.W. Gray, et al., Proc. Natl. Acad. Sci. U. S. A. 109 (2012) 2228–2233.
24
M. Taki, S. Iyoshi, A. Ojida, et al., J. Am. Chem. Soc. 132 (2010) 5938–5939.
25
T. Xiao, C.M. Ackerman, E.C. Carroll, et al., Nat. Chem. Biol. 14 (2018) 655–663.
26
L. Yang, R. McRae, M.M. Henary, et al., Proc. Natl. Acad. Sci. U. S. A. 102 (2005) 11179–11184.
27
L. Zeng, E.W. Miller, A. Pralle, et al., J. Am. Chem. Soc. 128 (2006) 10–11.
28
K.P. Carter, A.M. Young, A.E. Palmer, Chem. Rev. 114 (2014) 4564–4601.
29
E. Falcone, A. Sour, V. Lebrun, et al., Dalton Trans. 48 (2019) 14233–14237.
30
S. Lee, C.Y. Chung, P. Liu, et al., J. Am. Chem. Soc. 142 (2020) 14993–15003.
31
T. Miki, M. Awa, Y. Nishikawa, et al., Nat. Methods 13 (2016) 931–937.
32
F.H. Lu, P. Yue, X.R. Wang, Z.L. Lu, Inorg. Chem. Commun. 34 (2013) 19–22.
33
M.L. Giuffrida, G. Trusso Sfrazzetto, C. Satriano, et al., Inorg. Chem. 57 (2018) 2365–2368.
34
M. Kaur, Y.H. Ahn, K. Choi, et al., Org. Biomol. Chem. 13 (2015) 7149–7153.
35
W.L. Lee, T.W. Hsu, W.C. Hung, J.M. Fang, Dalton Trans. 48 (2019) 8026–8029.
36
S.R. Adusumalli, D.G. Rawale, K. Thakur, et al., Angew. Chem. Int. Ed. 59 (2020) 10332–10336.
37
N.C. Reddy, M. Kumar, R. Molla, V. Rai, Org. Biomol. Chem. 18 (2020) 4669–4691.
38
X. Chen, H. Ma, Anal. Chim. Acta 575 (2006) 217–222.
39
J. Xu, Y. Hou, Q. Ma, et al., Spectrochim. Acta A: Mol. Biomol. Spectrosc. 124 (2014) 416–422.
40
H.T. Zhi, Z. Lu, L. Chen, et al., Bioorg. Chem. 147 (2024) 107421.
Year 2026 volume 37 Issue 9
PDF
56
31
Cite this Article
BibTeX
Article Info
doi: 10.1016/j.cclet.2025.111924
  • Receive Date:2025-06-22
  • Online Date:2026-10-27
  • Published:2026-09-15
Article Data
Affiliations
History
  • Received:2025-06-22
  • Revised:2025-09-28
  • Accepted:2025-09-29
Affiliations
    aSchool of Pharmacy, Fudan University, Shanghai 201203, China
    bInstitute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
    cQuzhou Fudan Institute, Quzhou 324002, China

Corresponding:

*

E-mail addresses: (M. Uesugi)
References
Share
https://castjournals.cast.org.cn/joweb/ccl/EN/10.1016/j.cclet.2025.111924
Share to
QR

Scan QR to access full text

Cite this article
BibTeX
Citations
表12种不同金属材料的力学参数
科
Family
属数
Number of
genus
种数
Number of
species
占总种数比例
Percentage of
total species (%)
属
Genus
种数
Number of
species
占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
关闭全屏
  • BibTeX
  • EndNote
  • RefWorks
  • TxT