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Naphth[1,2-d]imidazoles Bioactive from β-Lapachone: Fluorescent Probes and Cytotoxic Agents to Cancer Cells

Graduate Program in Health and Biological Sciences, Universidade Federal do Vale do São Francisco, Av. José de Sá Maniçoba s/n, Campus Centro, Petrolina 56304-917, Brazil
Graduate Program in Materials Science, Universidade Federal do Vale do São Francisco, Av. Antônio Carlos Magalhães 510, Campus Juazeiro, Juazeiro 48902-300, Brazil
Graduate Program in Biotechnology, Rede Nordeste de Biotecnologia—RENORBIO, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Campus Lagoa Nova, Natal 59078-900, Brazil
Graduate Program in Pharmaceutical Sciences, Universidade Federal do Piauí, Teresina 64049-550, Brazil
Graduate Program in Physiology and Pharmacology, Universidade Federal do Ceará, Fortaleza 60430-270, Brazil
Author to whom correspondence should be addressed.
Molecules 2023, 28(7), 3008;
Received: 23 February 2023 / Revised: 16 March 2023 / Accepted: 18 March 2023 / Published: 28 March 2023
(This article belongs to the Special Issue Heterocycles: Design, Synthesis and Biological Evaluation)


Theranostics combines therapeutic and imaging diagnostic techniques that are extremely dependent on the action of imaging agent, transporter of therapeutic molecules, and specific target ligand, in which fluorescent probes can act as diagnostic agents. In particular, naphthoimidazoles are potential bioactive heterocycle compounds to be used in several biomedical applications. With this aim, a group of seven naphth[1,2-d]imidazole compounds were synthesized from β-lapachone. Their optical properties and their cytotoxic activity against cancer cells and their compounds were evaluated and confirmed promising values for molar absorptivity coefficients (on the order of 103 to 104), intense fluorescence emissions in the blue region, and large Stokes shifts (20–103 nm). Furthermore, the probes were also selective for analyzed cancer cells (leukemic cells (HL-60). The naphth[1,2-d]imidazoles showed IC50 between 8.71 and 29.92 μM against HL-60 cells. For HCT-116 cells, values for IC50 between 21.12 and 62.11 μM were observed. The selective cytotoxicity towards cancer cells and the fluorescence of the synthesized naphth[1,2-d]imidazoles are promising responses that make possible the application of these components in antitumor theranostic systems.

Graphical Abstract

1. Introduction

The multifunctionality of theranostic agents introduces several advantages for medicine, overcoming pharmacokinetic and selectivity issues of conventional therapy and diagnostic agents [1], while providing the image monitoring of pathology progression as well as the pharmacokinetic profile of the drug in the body [2].
The design of a theranostic agent requires a combination of different areas, such as chemistry, physics, nanotechnology, biochemistry, and engineering, with the aim of obtaining a multifunctional platform capable of performing non-invasive therapy and diagnosis of a pathological condition [3]. Typically, a theranostic agent is composed of (i) an imaging agent, (ii) a therapeutic molecule, (iii) a target-specific ligand, and (iv) a carrier. The diagnostic agent is a fundamental part of a theranostic system. It favors the non-invasive visualization of cellular and subcellular processes of a pathological condition through image emission. Examples of these components include fluorophores with the ability to respond to specific stimuli regarding the identification of biological species [4,5].
Fluorescent compounds, such as naphthoxazoles, have been explored as active molecules in biological systems [6]. Imidazoles and oxazoles can be synthesized through a multicomponent reaction, the Debus–Radziszewski reaction, employing α-dicarbonyl compounds and aldehydes [7,8]. The same reaction generates naphthoimidazoles and naphthoxazoles in which 1,2-naphthoquinones are used as α-dicarbonyl compounds [9,10]. β-Lapachone is a 1,2-naphthoquinone originally isolated from the heartwood of Handroanthus impetiginosus [11], which can be considered a potential antitumor agent [12,13,14]. The efficacy of β-lapachone for cancer treatment was evaluated through phase I and II clinical trials, with the naphthoquinone in the form of ARQ 501 and ARQ 761 [15,16,17,18]. However, several drawbacks of β-lapachone, such as low water solubility and narrow therapeutic windows, limited its clinical applications [19,20].
Based on the cytotoxicity of β-lapachone and the fluorescent properties of naphthoazole heterocycles, the scaffold 1,2-naphtho[1,2-d]imidazole was designed to be a fluorescent emitter with antitumor action, being considered a promising component of theranostic systems, as shown in Figure 1.
Herein, it is reported the synthesis of different naphth[1,2-d]imidazoles, with modification of substituents at the C2 position of the naphthoimidazole ring, and the following evaluation of their photophysical and anticancer activity as a part of a strategy to provide a new class of materials with promising biomedical applicability.

2. Results and Discussion

Naphth[1,2-d]imidazoles IM1IM7 were prepared in two steps (Scheme 1) from lapachol 1, in which the natural 1,4-naphthoquinone was extracted from the heartwood of trees of the genus Tabebuia. In the first step, β-lapachone (β-Lap 2) was obtained from the acid-catalyzed cyclization of lapachol 1 using sulfuric acid (H2SO4). In the following step, the compounds IM1IM7 were synthesized through the Debus–Radziszewski reaction, in a one-pot process between β-Lap 2 and the corresponding aldehyde, using ammonium acetate as a source of ammonia (Scheme 1). The reactions were established at 70 °C in acetic acid with a reaction time range of 0.5–4.0 h. The crude reactions were treated with sodium bisulfite (NaHSO3), and the products were purified using column chromatography or recrystallization. The naphthoimidazoles returned yields in the range of 9.9 to 52.0%, and their structures were scrutinized by analyzing the 1D and 2D Nuclear Magnetic Resonance (NMR) spectra, mass spectroscopy, and Fourier Transform Infrared (FTIR).

2.1. Optical Properties—Studies of Absorption and Fluorescence Spectra

Fluorescent molecules with the ability to absorb ultraviolet radiation and to emit in a range of wavelengths greater than that absorbed, that is, in the visible region, are extremely important to biomedical applications [21]. The characteristic time for the fluorescence process (on the order of 10−9 s) depends on the interaction of molecules with the surrounding environment, being attractive for the evaluation of several phenomena from the biophysical properties of molecules [21]. Thus, the photophysical study of the naphth[1,2-d]imidazoles IM1IM7 synthesized was carried out to verify their potential to emission of molecules for potential use in theranostic systems. The data for Ultraviolet–visible (UV–vis) absorption and fluorescence spectroscopy from naphth[1,2-d]imidazoles IM1IM7 are summarized in Table 1.

2.1.1. Solvatochromism Study

The dispersed molecules in a specific solvent can interact with other molecules of a fluorophore, affecting their emissive properties [22]. This phenomenon is called solvatochromism and depends on factors such as the polarity of the solvent, hydrogen bonding ability, pH, and viscosity of the solvent [22,23]. Considering the application of fluorescent probes in living cells and tissues, the solvatochromism study can evaluate the sensitivity and selectivity of the new compounds [24].
The influence of the solvent on optical characteristics of the synthesized naphth[1,2-d]imidazoles IM1IM7 was evaluated from the solvatochromism study that considered four solvents: hexane, dichloromethane (CH2Cl2), dimethyl sulfoxide (DMSO), and methanol (CH3OH) (Table S1). From the UV–vis absorption spectra of the naphtha[1,2-d]imidazoles (for different solvents), it was possible to determine the most suitable solvents and wavelengths for further photophysical studies. The criteria considered solvents for naphth[1,2-d]imidazoles that presented positive solvatochromism, i.e., redshift with increasing polarity of the solvent.
The absorption spectra of 2-substituted naphth[1,2-d]imidazoles (IM2IM7) showed two absorption bands in the ultraviolet region, corresponding to the π→π* transition of the substituent at the carbon C2 of the naphthoimidazole ring (~314 nm) and of the imidazole ring (~363 nm) [25,26,27] (Table S1).
The naphth[1,2-d]imidazoles IM2 and IM6 showed a higher bathochromic shift for polar solvents, a strong influence of the increasing solvent polarity on the absorption spectrum of these derivatives. On the other hand, IM7 showed a positive bathochromic effect in comparison to hexane, a nonpolar solvent. The other naphthoimidazoles (IM1, IM3, IM4, and IM5) exhibited an increasing redshift in CH2Cl2 (Table S1).

2.1.2. Molar Absorption Coefficient

The molar absorption coefficient (εAbs) is also an important parameter for the development of fluorescent probes. Samples prepared with naphth[1,2-d]imidazoles IM1IM7 showed high εAbs on the order of 103 to 104 M−1 cm−1 (Table 1), which is consistent with the allowed transition π→π* of π-conjugated systems [26,28,29,30] characteristic of the imidazole nucleus [25,31].
Table 1. Photophysical properties of the naphth[1,2-d]imidazoles IM1IM7.
Table 1. Photophysical properties of the naphth[1,2-d]imidazoles IM1IM7.
εAbs a
(104 M−1cm−1)
λemis b
DAPIH2O343 d-452112
a: Molar absorptivity coefficient at the concentration of 20 μM. b: Emission wavelength after excitation at 345 nm. c: Stokes shift. d: Data obtained from Farahat et al. (2017) [32].

2.1.3. Fluorescence Spectroscopy Experiments

Considering the UV–vis absorption spectra of the naphth[1,2-d]imidazoles IM1IM7, the excitation wavelength of 345 nm was chosen to obtain the fluorescence spectra. Analyzing the fluorescence emission spectra of compounds IM1IM7, the emission was observed in the UV–vis region, between the λemis values of 366 and 457 nm (Figure 2). IM3emis 457 nm) and IM5emis 422 nm), emitted at lower energy wavelengths, shifted more to the blue region. On the other hand, IM1, emitted at a higher energy wavelength, shifted toward the violet region (Figure 2).
In addition, IM2 (2.49 × 106 au) and IM3 (1.41 × 106 au) showed fluorescence emission intensities that were thirty-six and twenty-three times greater, respectively, than IM1 (6.90 × 104 au), indicating that the substitution at the carbon C2 of the naphthoimidazole ring favored the fluorescence emission of naphth[1,2-d]imidazoles IM1IM7 (Figure 2). The increase in the fluorescence evaluated by the substitution of the carbon C2 position is due to the increase in the conjugation of double bonds, providing more-effective intramolecular displacement of electrons [25,33].
By comparison between the fluorescence of IM4, IM5, and IM6, a positive influence on fluorescence was observed in compounds containing electron-donor substituents in the aromatic ring located at C2 of the naphth[1,2-d]imidazoles with IM4 and IM5 substituted with 4-hydroxyphenyl and 4-dimethylaminophenyl, respectively, showing higher fluorescence intensity than IM6, substituted with 4-nitrophenyl. The higher fluorescence of IM4 and IM5, if compared with other fluorophores, is attributed to a possible intramolecular charge transfer (ICT) [34].
Considering the fluorescence intensity emitted, the IM2, followed by the IM3, IM4, and IM5 compounds, showed the best results. All samples presented higher fluorescence than that observed for the 4′,6-diamidino-2-phenylindole (DAPI), the fluorescent DNA marker [35].
DAPI exhibits photophysical characteristics of absorption and emission (λabs 340 nm and λemis 453–461 nm) similar to the synthesized naphth[1,2-d]imidazoles. By comparison of the fluorescence emission of DAPI (1.13 × 105 au) to that of IM2 (2.49 × 106 au), IM3 (1.41 × 106 au), IM4 (1.36 × 106 au), and IM5 (7.04 × 105 au), it was observed that IM compounds also present more intense fluorescence in the blue region than DAPI. This may be due to the extension of the conjugated double-bond system of the synthesized naphth[1,2-d]imidazoles enhanced by the presence of the naphthalene system associated with the 2-substituted imidazole (Figure 3).

2.1.4. Stokes Shift

Fluorophores with large Stokes shifts (ΔST) are considered promising fluorescent probes for application in vivo cell-imaging studies, since they could minimize the background fluorescence in live tissues [36,37,38,39,40]. The naphth[1,2-d]imidazoles IM1IM7 presented ΔST between 20 and 103 nm (Table 2). If compared with the structure and ΔST of naphth[1,2-d]imidazoles IM1IM7, it was observed that the substituents at C2 affect the ability of this compound to be a fluorophore. IM1 has no substituents on C2 and was the one with the smallest ΔST, as well as the lowest fluorescence emission (6.90 × 104 au). IM3 presented the largest displacement, which is substituted at C2 with a naphthyl group. It was also observed that the introduction of electron-withdrawing substituents, such as nitrophenyl, produced naphthoimidazoles with narrow ΔST, as shown for IM6ST 20 nm) and IM7ST 48 nm).

2.2. Cytotoxicity Assay

The cytotoxic activity of the naphth[1,2-d]imidazoles IM1IM7 was assessed through colorimetric MTT assay [41,42]. The ability of these compounds to inhibit cell growth against human glioblastoma (SNB-19), human colorectal carcinoma (HCT-116), and human promyelocytic leukemia (HL-60) cell lines was evaluated. The IC50 was determined for those compounds, returning a percentage inhibition of cell growth above 75% in at least two tested cell lines. Thus, from all seven naphth[1,2-d]imidazoles tested (IM1IM7), only IM3 displayed low growth inhibition against all cell lines and did not have the IC50 calculated due to low cytotoxic activity. Doxorubicin was used as the positive control, and cytotoxic activities were expressed as IC50 for all the naphth[1,2-d]imidazoles in Table 2. The substances that displayed significant results against the cancer cell lines were also investigated against a nontumor cell line of murine fibroblast (L929) to evaluate their selectivity index (SI) (Table 2).
As shown in Table 2, most of the naphth[1,2-d]imidazoles are characterized by a certain degree of cytotoxicity against at least one of the malignant cell lines tested. The IC50 data showed that IM1 was the least potent imidazole of the series, demonstrating the importance of the substitution at the C2 carbon of the naphth[1,2-d]imidazole ring for the cytotoxic activity against the tested cancer cell lines. If considering the comparison of the influence of substituents at the C2 position, a significant decrease in cell growth inhibition was observed for naphthoimidazole with a naphthyl ring at C2 (IM3), suggesting that the phenyl substituent at the C2 position of the naphthoimidazole ring is relevant for the evaluated activity.
Against glioblastoma cells (SNB-19), the most cytotoxic compound was IM5 (IC50 21.05 μM). As for HCT-116 cells and leukemia cells (HL-60), the most active naphth[1,2-d]imidazoles were IM6 and IM4, with IC50 of 21.12 and 8.71 μM, respectively. Comparing the three most cytotoxic imidazoles (IM4, IM5, and IM6) for each cancer cell line tested, it was observed that all of them presented as a substituent at the C2 position a 4-substituted phenyl ring with an electronegative group: -OH, -N(CH3)2, and NO2, respectively. Thus, it is possible to suggest that the substituted phenyl group located at the C2 carbon of the naphthoimidazole ring improves cytotoxicity activity and promotes selectivity.
In addition, for the cytotoxic activity of IM6 and IM7 (Table 2) for each cancer cell line tested, it can be seen that the 2-nitrophenyl substituent group at the C2 carbon of the naphthoimidazole ring makes the compound less cytotoxic to the evaluated tumor cell lines. Comparing the cytotoxic activity against three cancer cell lines, the tested naphthoimidazoles showed to be more active against the leukemia cell line (HL-60), presenting IC50 between 8.71 and 29.92 μM. Among them, IM4 was the most active compound, with an emphasis on its high selectivity for leukemic cells (SI > 41.67).
By considering that high εAbs values combined with large ΔST are desirable for fluorescent probes [43] and the photophysical and cytotoxic properties of each naphth[1,2-d]imidazole, one can infer that IM3 (fluorescence intensity 1.41 × 106 au, εAbs 1.57 × 104 M−1 cm−1 and ΔST 103 nm) fits as a good fluorescent probe; however, it showed low cytotoxicity on the cell lines tested. One can also infer that IM2 (fluorescence intensity 2.49 × 106 au; εAbs 2.43 × 104 M−1 cm−1 and ΔST 60 nm) has photophysical properties that qualify it as a fluorescent probe, and it has cytotoxicity against HCT-116 (IC50 21.69 µM) and selectivity (SI 4.83).
IM4 stands out for cytotoxicity against HL-60 (IC50 8.71 µM) and selectivity (SI > 41.70); at the same time, it appears to have a high intensity of fluorescence (1.36 × 106 au) and moderate εAbs (1.48 × 104 M−1 cm−1) and ΔST 49 nm. IM5 was cytotoxic to SNB-19 (IC50 21.05 µM and SI 2.51) and showed promising photophysical properties (fluorescence 7.04 × 105 au; εAbs 2.71 × 104 M−1 cm−1 and ΔST 54 nm).

3. Materials and Methods

3.1. Materials

All chemicals were purchased from commercial suppliers and used without further purification. Melting points were determined through a PFM-II (Instrumentation MS Tecnopon®) melting-point apparatus. The purity of the compounds synthesized was determined by thin-layer chromatography (TLC) using several solvent systems of different polarities. Purification of these compounds was done by column chromatography. Infrared (IR) spectra were recorded on a PerkinElmer (model 10.4.00) spectrophotometer equipped with an Attenuated Total Reflectance ATR sampling unit. NMR spectra were recorded on a Bruker Ascend 400 spectrometer, operating at 400 MHz for 1H NMR and 100 MHz for 13C NMR. CDCl3 and DMSO-d6 were used as solvents with tetramethylsilane (TMS) as the internal standard; chemical shifts (δ) are given in ppm and coupling constants (J) in Hz. Mass spectra were recorded with a Bruker Daltonics (TOF-Q-II) spectrometer using electrospray ionization. UV–vis absorption spectra were obtained using a Hach/Lange spectrophotometer (model DR 5000). Fluorescence emission spectra were obtained using the ISS spectrofluorometer (model PC1).

3.2. Synthesis of Naphth[1,2-d]imidazoles IM1IM7

3.2.1. Synthesis of β-Lapachone 2

Lapachol 1 was extracted from the wood of a plant of the genus Tabebuia and used after purification and identification, as described previously [44]. The access was registered in the National System of Genetic Heritage and Associated Traditional Knowledge (SISGEN) under the A5FDA89. Yield: 1.5% (m/m). Yellow solid, mp: 138.3–140.3 °C (Lit 139.0–141.0 °C) [45].
In a 25 mL reaction flask, the lapachol (484 mg, 2 mmol) was weighed and incorporated into a concentrated sulfuric acid (H2SO4) solution (5 mL). The reaction mixture was stirred at room temperature for 1.0 h, then poured into 400 mL of ice-cold deionized water. The solid obtained was vacuum filtered and allowed to dry at room temperature [44], which resulted in a yield of 95%. Orange solid, mp: 155 °C (Lit 154–155 °C) [46]. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 7.91 (d, J = 7.6 Hz, 1H), 7.77 (m, 2H), 7.61 (m, 1H), 2.40 (t, J = 6.6 Hz, 2H), 1.82 (t, J = 6.6 Hz, 2H), 1.43 (s, 6H). 13C NMR (100 MHz DMSO-d6) δ (ppm): 179.1, 177.8, 160.6, 135.0, 132.1, 130.8, 129.9, 127.8, 123.7, 112.5, 79.0, 30.8, 26.3, 15.9.

3.2.2. General Synthesis of the Naphth[1,2-d]imidazoles

The solution of β-Lap 2 (242 mg; 1.0 mmol) was prepared in glacial acetic acid (6 mL), and was added aldehyde adequate (2.5 mmol). The reaction mixture was placed at a temperature of 70 °C and added to ammonium acetate (1.27 g; 16.5 mmol) that was divided into three parts and remained at this temperature under stirring until the end of the reaction [10]. The reactions were followed by Thin Layer Chromatography (TLC), and the reaction times varied in the range of 30 min to 4 h. In experiments using 4-dimethylaminobenzaldehyde and 4-nitrobenzaldehyde, there was a precipitate formation in the reaction. However, in experiments employing formaldehyde, benzaldehyde, 1-naphthaldehyde, 4-hydroxybenzaldehyde, and 2-nitrobenzaldehyde, there was no precipitate formation in the reaction. Then, after the reaction time, the reaction mixture was poured into a cold solution of 5.0% (m/v) of NaHSO3 for precipitate formation. The solid was filtered and washed with a solution of 5.0% (m/v) of NaHCO3, and water was deionized at neutral pH and dried at room temperature.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-pyran[b-4,3]naphth[1,2-d]imidazole (IM1)

The reaction was heated to 70 °C for 4.0 h. Compound IM1 was obtained as a yellow crystalline solid (131 mg, 0.519 mmol, yield: 52.0%), mp: 255–259 °C. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 8.30 (d, J = 8.0 Hz, 1H), 8.17 (s, 1H), 8.12 (d, 1H), 7.54 (t, 1H), 7.42 (t, 1H), 2.98 (t, 2H), 1.94 (t, 2H), 1.40 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 143.9, 132.9, 138.4, 127.7, 125.7, 124.1, 123.3, 122.7, 122.1, 121.0, 104.4, 74.2, 31.5, 26.5, 18.5. IR (KBr) ʋmax/cm−1: 3435, 3088, 2971, 2925, 2841, 1608, 1538, 1484, 1453, 1362, 1252, 1164, 1122, 1054, 947, and 770, Figure S1.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(phenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM2)

The reaction was heated to 70 °C for 1.0 h. Compound IM2 was obtained as a light-yellow solid (60 mg, 0.183 mmol, yield: 18.3%), mp: 278–279 °C. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 13.24 (s, 0.3H), 12.76 (s, 0.5H), 8.37–8.46 (m, 1H), 8.20–8.29 (m, 2H), 8.10–8.20 (m, 1H), 7.51–7.63 (m, 3H), 7.39-7.51 (m, 2H), 3.00–3.17(m, 2H), 1.87–2.06 (m, 2H), 1.43 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 147.9, 144.5, 132.2, 131.2, 130.6, 129.1, 128.8, 126.0, 125.9, 125.7, 123.4, 122.8, 122.1, 121.2, 102.4, 74.4, 31.4, 26.5, 18.8. IR (KBr) ʋmax/cm−1: 3432, 3067, 2972, 2852, 2928, 1600, 1520, 1256, 1157, and 1056. HRMS (ESI-TOF) calculated for C22H20N2O [M+H]+: 329.1609. Found: 329.1646, Figure S2.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(naphthalenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM3)

The reaction was heated to 70 °C for 2.0 h. Compound IM3 was obtained as a pale-yellow solid (83 mg, 0.22 mmol, yield: 25.4%). 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 13.39 (s, 0.4H); 12,92 (s, 0.6H); 9.15 (dd, 1H); 8.45 (dd, 1H); 8.19 (d, J = 7.9 Hz, 1H); 8.02–8.12 (m, 3H); 7.55–7.74 (m, 4H); 7.41–7.49 (m, 1H); 3.06 (m, 1.2H); 3.18 (m, 0.8H); 2.00 (m, 2H); 1.45 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 147.7, 144,5, 133.6, 132.2, 130.6, 130.5, 129.4, 129.2, 128.0, 128.2, 127.5, 126.5, 126.1, 125.8, 125.7, 125.2, 123.3, 122.8, 122.1, 121.1, 102.3, 74.3, 31.4, 26.4, 18.7. IR (KBr) ʋmax/cm−1: 3405, 3061, 2977, 2929, 1588, 1518, 1257, 1121, and 1054. HRMS (ESI-TOF) calculated for C26H22N2O2 [M+H]+: 378.1732. Found: 379.1802, Figure S3.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(4-hidroxyphenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM4)

The reaction was heated to 70 °C for 1.0 h. Compound IM4 was obtained as a gray amorphous solid (34 mg, 0.099 mmol, yield: 9.9%). 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 12.97 (s, 0.3H), 12.49 (s, 0.5H), 9.85 (s, 1H), 8.32-8.41 (m, 1H), 8.13 (d, 1H), 8.08 (d, 2H), 7.49–7.59 (m, 1H), 7.33–7.44 (m, 1H), 6.92 (d, J = 8.2 Hz, 2H), 2.96–3.14 (m, 2H), 1.89–1.98 (m, 2H), 1.42 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 158.3, 148.4, 143.9, 131.9, 130.7, 127.5, 125.5, 125.4, 123.0, 121.9, 121.9, 121.7, 121.0, 115.4, 102.3, 74.1, 31.3, 26.4, 18.7. IR (KBr) ʋmax/cm−1: 3422, 3071, 2974, 2849, 2929,1613, 1533, 1265, 1160, and 1055. HRMS (ESI-TOF) calculated for C22H20N2O2 [M+H]+: 345.1558. Found: 345.1590, Figure S4.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(4-dimethylaminophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM5)

The reaction was heated to 70 °C for 3.0 h. Compound IM5 was obtained as a light-yellow solid (121 mg, 0.326 mmol, yield: 32.6%), mp: 182-184 °C. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 12.87 (s, 0.4H), 12.42 (s, 0.5H), 8.30–8.42 (m, 1H), 8.03–8.17 (m, 3H), 7.53 (t, J = 7.3 Hz, 1H), 7.38 (t, J = 7.6 Hz, 1H), 6.86 (d, J = 8.7 Hz, 2H), 2.95–3.14 (m, 8H), 1.93–2,01 (m, 2H), 1.41 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 150.7, 150.6, 143.8, 130.8, 127.1, 125.5, 123.0, 122.4, 122.1, 121.2, 120.3, 112.0, 102.5, 74.1, 40.0, 31.5, 26.5, 18.9. IR (KBr) ʋmax/cm−1: 3432, 3067, 2979, 2841, 2930, 1610, 1518, 1256, 1159, and 1055. HRMS (ESI-TOF) calculated for C24H25N3O [M+H]+: 372.2031. Found: 372.2073, Figure S5.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(4-nitrophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM6)

The reaction was heated to 70 °C for 30 min. Compound IM6 was obtained as a red crystalline solid (183 mg, 0.490 mmol, yield: 49.1%), mp: 259–260 °C. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 13.61 (s, 0.3H), 13.10 (s, 0.6H), 8.36–8.52 (m, 5H), 8.13–8.22 (m, 1H), 7.56–7.67 (m, 1H), 2.96–3.16 (m, 2H), 1.90–2.09 (m, 2H), 1.42, 144 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 146.8, 146.6, 144.2, 136.6, 133.0, 132.1, 126.6, 126.3, 125.7, 124.3, 124.0, 123.2, 122.3, 121.2, 102.2, 74.7, 31.3, 26.5, 18.7. IR (KBr) ʋmax/cm−1: 3348, 2975, 2845, 2929, 1604, 1511, 1258, 1155, and 1057. HRMS (ESI-TOF) calculated for C22H19N3O3 [M+H]+: 374.1460. Found: 374.1511, Figure S6.

Synthesis of 4,5-dihydro-6,6-dimethyl-6H-2-(2-nitrophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM7)

The reaction was heated to 70 °C for 2.5 h. Compound IM7 was obtained as a red solid (194 mg, 0.520 mmol, yield: 52.0%), mp: 139-141 °C. 1H NMR (400 MHz, DMSO-d6) δ [ppm]: 13.52 (s, 0.3H), 13.08 (s, 0.7H), 8.27 (d, 1H), 8.20–8.11 (m, 1H), 8.03 (t, J = 8.7 Hz, 2H), 7.83–7.92 (m, 1H), 7.68–7.77 (m, 1H), 7.53–7.63 (m, 1H), 7.41–7.50 (m, 1H), 2.99 (t, J = 6.5 Hz, 2H), 1.99 (t, J = 6.6 Hz, 2H), 1.43, 1.41 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ [ppm]: 148.8, 144.7, 143.8, 132.4, 132.6, 131.2, 130.9, 130.3, 126.1, 125.6, 124.6, 124.4, 123.7, 123.2, 122.2, 121.1, 102.2, 74.6, 31.4, 26.5, 18.7. IR (KBr) ʋmax/cm−1: 3415, 3116, 2973, 2850, 2923, 1602, 1521, 1260, 1162, and 1057. HRMS (ESI-TOF) calculated for C22H19N3O3 [M+H]+: 374.1460. Found: 374.1495, Figure S7.

3.3. Evaluation of Photophysical Properties

3.3.1. Obtaining Visible Ultraviolet Absorption Spectra

A stock solution in dichloromethane (CH2Cl2) of each compound was prepared at a concentration of 4000 µM. From the stock solution, solutions were prepared at a concentration of 20 µM of each compound in four different solvents: hexane, CH2Cl2, dimethyl sulfoxide (DMSO), and methanol (CH3OH). Then, measurement in the range of 190 to 800 nm was performed, with the wavelengths of maximum absorption (λmax) of the compounds in the different solvents shown in Table S1 and Figure S8.

3.3.2. Molar Absorptivity Coefficient

The molar absorptivity coefficient (εAbs) was determined using an equation applied by Lambert–Beer (εAbs = A/LxC, where A—maximum absorbance; L—the optical path of the cuvette used (1 cm); and C—concentration of the analyzed sample in M).

3.3.3. Fluorescence Emission Spectrum and Stokes Shift

Stock solutions used for each compound, at a concentration of 4000 µM, in the solvents in which the sample showed better resolution of the maximum absorption band, were DMSO for IM2, CH3OH for IM6, hexane for IM7, and CH2Cl2 for the others. The stock solutions were diluted to a concentration of 20 µM, and readings used the excitation wavelength of 345 nm for all compounds. The Stokes shift (ΔST) was calculated from the difference between the absorbance and excitation wavelengths (λAbs–λEmis), Figure S8.

3.4. Evaluation of the Cytotoxic Activity

3.4.1. Cell Lines

Brain tumor (SNB-19), human colorectal carcinoma (HCT-116), and human promyelocytic leukemia (HL-60) cells were obtained from the National Cancer Institute (NCI) (Bethesda, MD, USA). The L929 cells (mouse fibroblast L cells NCTC clone 929) were purchased from the American Type Culture Collection (Manassas, VA, USA). The cells were grown on RPMI 1640 medium supplemented with 10% fetal bovine serum and 1% antibiotics (penicillin/streptomycin) at 37 °C with 5% CO2.

3.4.2. Assessment of In Vitro Anticancer Activity

Cytotoxic potential of the naphth[1,2-d]imidazoles IM1IM7 was assessed after 72 h of exposure to the tumor cell lines of human SNB-19, HCT-116, HL-60, and normal cell line L929. Cells were plated in 96-well plates (0.7 × 105 cells/well for SNB-19, 0.3 × 106 cells/well for HCT-116, and 0.3 × 106 cells/well for HL-60). Compounds were dissolved with DMSO at concentrations in the 0.078–10 μg.mL−1 range. Doxorubicin (0.001–1.10 μM) was used as the positive control, and negative control groups received the same amount of vehicle (DMSO). The cell viability was determined by the reduction of the yellow dye 3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide (MTT) to a blue formazan product [35]. At the end of the incubation time (69 h), the plates were centrifuged, and the medium was replaced with fresh medium (200 μL) containing 0.5 mg/mL of MTT. Three hours later, the MTT formazan product was dissolved in DMSO (150 μL), and the absorbance was measured using a multi-plate reader (Spectra Count, Packard, ON, Canada). The drug effect was quantified as the percentage of control absorbance of the reduced dye at 550 nm. All experiments were performed in three independent assays, and the half maximal inhibitory concentration (IC50) and their 95% confidence intervals were achieved by nonlinear regression.

4. Conclusions

Naphth[1,2-d]imidazoles IM1IM7 showed high levels of cytotoxic activity and selectivity against the tested cancer cells and promising optical properties. The cytotoxicity results and photophysical properties presented by naphth[1,2-d]imidazoles IM2, IM3, IM4, and IM5 qualify them for further studies in the development of fluorescent anticancer probes using this scaffold, making possible the use of naphth[1,2-d]imidazoles as fluorescent probes/therapeutic molecules in theranostic systems for cancer treatment/diagnosis.

Supplementary Materials

The following supporting information can be downloaded at Figure S1: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-pyran[b-4,3]naphth[1,2-d]imidazole (IM1) in DMSO-d6; Figure S2: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(phenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM2) in DMSO-d6 and ESI-MS; Figure S3: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(naphthalenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM3) in DMSO-d6and ESI-MS; Figure S4: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(4-hidroxyphenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM4) in DMSO-d6 and ESI-MS; Figure S5: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(4-dimethylaminophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM5) in DMSO-d6 and ESI-MS; Figure S6: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(4-nitrophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM6) in DMSO-d6 and ESI-MS; Figure S7: NMR spectra of 4,5-dihydro-6,6-dimethyl-6H-2-(2-nitrophenyl)-pyran[b-4,3]naphth[1,2-d]imidazole (IM7) in DMSO-d6and ESI-MS; Figure S8: Absorbance and emission spectra of naphthoimidazoles IM1IM7; Table S1: Wavelength (nm) and absorbance of the scanning spectra of the naphth[1,2-d]imidazoles obtained in the solvatochromism study.

Author Contributions

Conceptualization, V.L.d.A.S., H.P.d.O., C.P. and C.R.M.A.; formal analysis, V.L.d.A.S., A.d.A.G., M.P.d.C., F.d.C.E.d.O. and C.R.M.A.; funding acquisition, H.P.d.O., C.P. and C.R.M.A.; investigation, V.L.d.A.S., D.G.G., S.S.S. and L.P.S.R.; methodology, V.L.d.A.S., H.P.d.O., M.P.d.C. and F.d.C.E.d.O.; project administration, C.R.M.A.; writing—original draft, V.L.d.A.S. and C.R.M.A.; writing—review and editing, A.d.A.G., M.P.d.C. and C.R.M.A. All authors have read and agreed to the published version of the manuscript.


This research received funding from the Coordination of the Improvement of Higher Education Personnel (CAPES), Brazil, process no. 88881.708019/2022-01 of the PDPG-consolidação-3-4 program and Research Support Foundation of Pernambuco (FACEPE)—process no. IBPG-0457-1.06/20.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article or Supplementary Material.


We are grateful to the following Brazilian agencies: Coordination of the Improvement of Higher Education Personnel (CAPES) and Research Support Foundation of Pernambuco (FACEPE).

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.

Sample Availability

Samples of the compounds are available from the authors.


  1. Kelkar, S.S.; Reineke, T.M. Theranostics: Combining Imaging and Therapy. Bioconjugate Chem. 2011, 22, 1879–1903. [Google Scholar] [CrossRef]
  2. Xiao, S.; Tang, Y.; Lv, Z.; Lin, Y.; Chen, L. Nanomedicine—Advantages for their use in rheumatoid arthritis theranostics. J. Control. Release 2019, 316, 302–316. [Google Scholar] [CrossRef] [PubMed]
  3. Golovin, Y.; Klyachko, N.; Majouga, A.; Kabanov, A. Modeling drug release from functionalized magnetic nanoparticles actuated by non-heating low frequency magnetic field. J. Nanoparticle Res. 2017, 64, 19. [Google Scholar] [CrossRef]
  4. Jain, T.; Kumar, S.; Dutta, P.K. Theranostics: A Way of Modern Medical Diagnostics and the Role of Chitosan. J. Mol. Genet. Med. 2014, 9, 1000159. [Google Scholar] [CrossRef]
  5. Cole, J.T.; Holland, N.B. Multifunctional nanoparticles for use in theranostic applications. Drug Deliv. Transl. Res. 2015, 5, 295–309. [Google Scholar] [CrossRef]
  6. Santos, V.; Guimarães, D.; Nishimura, R.; Rolim, L.; Gonsalves, A.; Araújo, C. Naftoimidazóis e naftoxazóis—Promissores componentes de sistemas teranósticos. Quim. Nova 2022, 45, 560–577. [Google Scholar] [CrossRef]
  7. Kerru, N.; Bhaskaruni, S.V.H.S.; Gummidi, L.; Maddila, S.N.; Maddila, S.; Jonnalagadda, S.B. Recent advances in heterogeneous catalysts for the synthesis of imidazole derivatives. Synth. Commun. 2019, 49, 2437–2459. [Google Scholar] [CrossRef]
  8. Santos, V.; Gonsalves, A.; Araújo, C. Resgate da reação de debus-radziszewski: Ensino prático de reações multicomponentes na síntese da lofina. Quim. Nova 2020, 43, 1344–1349. [Google Scholar] [CrossRef]
  9. Bombaça, A.C.S.; Silva, L.A.; Chaves, O.A.; da Silva, L.S.; Barbosa, J.M.; da Silva, A.M.; Ferreira, A.B.; Menna-Barreto, R.F. Novel N,N-di-alkylnaphthoimidazolium derivative of β-lapachone impaired Trypanosoma cruzi mitochondrial electron transport system. Biomed. Pharmacother. 2021, 135, 111186. [Google Scholar] [CrossRef]
  10. Moura, K.C.; Carneiro, P.F.; Pinto, M.D.C.F.; da Silva, J.A.; Malta, V.; de Simone, C.A.; Dias, G.; Jardim, G.A.; Cantos, J.; Coelho, T.S.; et al. 1,3-Azoles from ortho-naphthoquinones: Synthesis of aryl substituted imidazoles and oxazoles and their potent activity against Mycobacterium tuberculosis. Bioorganic Med. Chem. 2012, 20, 6482–6488. [Google Scholar] [CrossRef]
  11. Castellanos, J.R.G.; Prieto, J.M.; Heinrich, M. Red Lapacho (Tabebuia impetiginosa)—A global ethnopharmacological commodity? J. Ethnopharmacol. 2009, 121, 1–13. [Google Scholar] [CrossRef] [PubMed]
  12. Moon, D.-O.; Kang, C.-H.; Kim, M.-O.; Jeon, Y.-J.; Lee, J.-D.; Choi, Y.H.; Kim, G.-Y. β-Lapachone (LAPA) Decreases Cell Viability and Telomerase Activity in Leukemia Cells: Suppression of Telomerase Activity by LAPA. J. Med. Food 2010, 13, 481–488. [Google Scholar] [CrossRef] [PubMed]
  13. Jardim, G.A.M.; Lima, D.J.B.; Valença, W.O.; Cavalcanti, B.C.; Pessoa, C.; Rafique, J.; Braga, A.L.; Jacob, C.; Da Silva Júnior, E.N.; Da Cruz, E.H.G. Synthesis of Selenium-Quinone Hybrid Compounds with Potential Antitumor Activity via Rh-Catalyzed C-H Bond Activation and Click Reactions. Molecules 2017, 23, 83. [Google Scholar] [CrossRef] [PubMed][Green Version]
  14. Costa, D.C.F.; Rangel, L.P.; Martins-Dinis, M.M.D.C.; Ferretti, G.D.S.; Ferreira, V.F.; Silva, J.L. Anticancer potential of resveratrol, β-lapachone and their analogues. Molecules 2020, 25, 893. [Google Scholar] [CrossRef][Green Version]
  15. Khong, H.T.; Dreisbach, L.; Kindler, H.L.; Trent, D.F.; Jeziorski, K.G.; Bonderenko, I.; Popiela, T.; Yagovane, D.M.; Dombal, G. A phase 2 study of ARQ 501 in combination with gemcitabine in adult patients with treatment naïve, unresectable pancreatic adenocarcinoma. J. Clin. Oncol. 2007, 25, 15017. [Google Scholar] [CrossRef]
  16. Kawecki, A.; Adkins, D.R.; Cunningham, C.C.; Vokes, E.; Yagovane, D.M.; Dombal, G.; Koralewski, P.; Hotko, Y.; Vladimirov, V. A phase II study of ARQ 501 in patients with advanced squamous cell carcinoma of the head and neck. J. Clin. Oncol. 2007, 25, 16509. [Google Scholar] [CrossRef]
  17. Gerber, D.E.; Beg, M.S.; Fattah, F.; Frankel, A.E.; Fatunde, O.; Arriaga, Y.; Dowell, J.E.; Bisen, A.; Leff, R.D.; Meek, C.C.; et al. Phase 1 study of ARQ 761, a β-lapachone analogue that promotes NQO1-mediated programmed cancer cell necrosis. Br. J. Cancer 2018, 119, 928–936. [Google Scholar] [CrossRef][Green Version]
  18. Kim, S.; Lee, S.; Cho, J.-Y.; Yoon, S.H.; Jang, I.-J.; Yu, K.-S. Pharmacokinetics and tolerability of MB12066, a beta-lapachone derivative targeting NAD(P)H:quinone oxidoreductase 1: Two independent, double-blind, placebo-controlled, combined single and multiple ascending dose first-in-human clinical trials. Drug Des. Dev. Ther. 2017, 11, 3187–3195. [Google Scholar] [CrossRef][Green Version]
  19. Kim, I.; Kim, H.; Ro, J.; Jo, K.; Karki, S.; Khadka, P.; Yun, G.; Lee, J. Preclinical Pharmacokinetic Evaluation of β-Lapachone: Characteristics of Oral Bioavailability and First-Pass Metabolism in Rats. Biomol. Ther. 2015, 23, 296–300. [Google Scholar] [CrossRef] [PubMed][Green Version]
  20. Blanco, E.; Bey, E.A.; Khemtong, C.; Yang, S.-G.; Setti-Guthi, J.; Chen, H.; Kessinger, C.W.; Carnevale, K.A.; Bornmann, W.G.; Boothman, D.A.; et al. β-Lapachone Micellar Nanotherapeutics for Non–Small Cell Lung Cancer Therapy. Cancer Res 2010, 70, 3896–3904. [Google Scholar] [CrossRef][Green Version]
  21. Pavoni, J.; Neves-Junior, W.; Spiropulos, M.; De Araujo, D. Uma montagem experimental para a medida de fluorescência. Rev. Bras. de Ensino de F?sica 2014, 36, 1–9. [Google Scholar] [CrossRef][Green Version]
  22. Bozkurt, E.; Dogan, S.D. Photophysical behavior of a novel 4-aza-indole derivative in different solvents: Reverse solvatochromism. Res. Chem. Intermed. 2018, 45, 863–872. [Google Scholar] [CrossRef]
  23. de Rezende, L.C.D.; Vaidergorn, M.M.; Moraes, J.C.B.; Emery, F.D.S. Synthesis, Photophysical Properties and Solvatochromism of Meso-Substituted Tetramethyl BODIPY Dyes. J. Fluoresc. 2013, 24, 257–266. [Google Scholar] [CrossRef] [PubMed]
  24. Telegin, F.Y.; Marfin, Y.S. New insights into quantifying the solvatochromism of BODIPY based fluorescent probes. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2021, 255, 119683. [Google Scholar] [CrossRef]
  25. Chen, S.; Hong, F. Palladium-Catalyzed C-H Functionalization of Amido-Substitued 1,4-Napthoquinone in the Presence of Amines toward the Formation of Pyrroles and Imidazoles. Chemistryselect 2017, 2, 10232–10238. [Google Scholar] [CrossRef]
  26. Nagarajan, N.; Vanitha, G.; Ananth, D.A.; Rameshkumar, A.; Sivasudha, T.; Renganathan, R. Bioimaging, antibacterial and antifungal properties of imidazole-pyridine fluorophores: Synthesis, characterization and solvatochromism. J. Photochem. Photobiol. B: Biol. 2013, 127, 212–222. [Google Scholar] [CrossRef]
  27. De Souza, V.P.; Vendrusculo, V.; Morás, A.M.; Steffens, L.; Santos, F.S.; Moura, D.J.; Rodembusch, F.S.; Russowsky, D. Synthesis and photophysical study of new fluorescent proton transfer dihydropyrimidinone hybrids as potential candidates for molecular probes. New J. Chem. 2017, 41, 15305–15311. [Google Scholar] [CrossRef]
  28. Valeur, B.; Berberan-Santos, M.N. Molecular fluorescence: Principles and applications, 2nd ed.; John Wiley & Sons: Weinheim, Germany, 2012. [Google Scholar]
  29. Liu, X.; Xu, Z.; Cole, J.M. Molecular Design of UV–vis Absorption and Emission Properties in Organic Fluorophores: Toward Larger Bathochromic Shifts, Enhanced Molar Extinction Coefficients, and Greater Stokes Shifts. J. Phys. Chem. C 2013, 117, 16584–16595. [Google Scholar] [CrossRef]
  30. Tariq, A.; Garnier, U.; Ghasemi, R.; Lefevre, J.P.; Mongin, C.; Brosseau, A.; Audibert, J.F.; Pansu, R.; Dauzères, A.; Leray, I. Perylene based PET fluorescent molecular probes for pH monitoring. J. Photochem. Photobiol. A Chem. 2022, 432, 114035. [Google Scholar] [CrossRef]
  31. Ghodbane, A.; Colléaux, J.; Saffon, N.; Mahiou, R.; Galaup, J.-P.; Fery-Forgues, S. Blue-Emitting Nanocrystals, Microcrystals, and Highly Oriented Nanofibers Prepared by Reprecipitation and Solvent Drop-Casting of 2-Phenyl-naphthoxazoles. Chempluschem 2012, 78, 185–191. [Google Scholar] [CrossRef]
  32. Farahat, A.A.; Kumar, A.; Say, M.; Wenzler, T.; Brun, R.; Paul, A.; Wilson, W.D.; Boykin, D.W. Exploration of DAPI analogues: Synthesis, antitrypanosomal activity, DNA binding and fluorescence properties. Eur. J. Med. Chem. 2017, 128, 70–78. [Google Scholar] [CrossRef] [PubMed][Green Version]
  33. Doğru, Ü.; Ürüt, G.; Bayramin, D. Synthesis and spectroscopic characterization of Y-shaped fluorophores with an imidazole core containing crown ether moieties. J. Lumin. 2015, 163, 32–39. [Google Scholar] [CrossRef]
  34. Chipem, F.A.S.; Mishra, A.; Krishnamoorthy, G. The role of hydrogen bonding in excited state intramolecular charge transfer. Phys. Chem. Chem. Phys. 2012, 14, 8775–8790. [Google Scholar] [CrossRef]
  35. Liu, T.; Zhang, J.; Cao, J.; Zheng, H.; Zhan, C.; Liu, H.; Zhang, L.; Xiao, K.; Liu, S.; Xiang, D.; et al. Identification of coexistence of biological and non-biological aerosol particles with DAPI (4′,6-diamidino-2-phenylindole) stain. Particuology 2023, 72, 49–57. [Google Scholar] [CrossRef]
  36. Hu, J.; Guo, Y.; Geng, X.; Wang, J.; Li, S.; Sun, Y.; Qu, L.; Li, Z. Tuning asymmetric electronic structure endows carbon dots with unexpected huge stokes shift for high contrast in vivo imaging. Chem. Eng. J. 2022, 446, 136928. [Google Scholar] [CrossRef]
  37. Araneda, J.F.; Piers, W.E.; Heyne, B.; Parvez, M.; McDonald, R. High Stokes Shift Anilido-Pyridine Boron Difluoride Dyes. Angew. Chem. Int. Ed. 2011, 50, 12214–12217. [Google Scholar] [CrossRef]
  38. Shcherbakova, D.M.; Hink, M.A.; Joosen, L.; Gadella, T.W.J.; Verkhusha, V.V. An Orange Fluorescent Protein with a Large Stokes Shift for Single-Excitation Multicolor FCCS and FRET Imaging. J. Am. Chem. Soc. 2012, 134, 7913–7923. [Google Scholar] [CrossRef] [PubMed][Green Version]
  39. Wu, X.; Sun, X.; Guo, Z.; Tang, J.; Shen, Y.; James, T.D.; Tian, H.; Zhu, W. In Vivo and in Situ Tracking Cancer Chemotherapy by Highly Photostable NIR Fluorescent Theranostic Prodrug. J. Am. Chem. Soc. 2014, 136, 3579–3588. [Google Scholar] [CrossRef] [PubMed]
  40. Wu, I.-C.; Yu, J.; Ye, F.; Rong, Y.; Gallina, M.E.; Fujimoto, B.S.; Zhang, Y.; Chan, Y.-H.; Sun, W.; Zhou, X.-H.; et al. Squaraine-Based Polymer Dots with Narrow, Bright Near-Infrared Fluorescence for Biological Applications. J. Am. Chem. Soc. 2014, 137, 173–178. [Google Scholar] [CrossRef] [PubMed][Green Version]
  41. Mosmann, T. Rapid colorimetric assay for cellular growth and survival: Application to proliferation and cytotoxicity assays. J. Immunol. Methods 1983, 65, 55–63. [Google Scholar] [CrossRef]
  42. Peña-Morán, O.A.; Villarreal, M.L.; Álvarez-Berber, L.; Meneses-Acosta, A.; Rodríguez-López, V. Cytotoxicity, Post-Treatment Recovery, and Selectivity Analysis of Naturally Occurring Podophyllotoxins from Bursera fagaroides var. fagaroides on Breast Cancer Cell Lines. Molecules 2016, 21, 1013. [Google Scholar] [CrossRef] [PubMed][Green Version]
  43. Zhang, J.; Chen, R.; Zhu, Z.; Adachi, C.; Zhang, X.; Lee, C.-S. Highly Stable Near-Infrared Fluorescent Organic Nanoparticles with a Large Stokes Shift for Noninvasive Long-Term Cellular Imaging. ACS Appl. Mater. Interfaces 2015, 7, 26266–26274. [Google Scholar] [CrossRef] [PubMed]
  44. Souza, M.A.A.D.; Silva, A.R.D.; Ferreira, M.A.; Lemos, M.J.D.; Ramos, R.G.; Ferreira, A.B.B.; Souza, S.R.D. Atividade biológica do lapachol e de alguns derivados sobre o desenvolvimento fúngico e em germinação de sementes. Quim. Nova 2008, 31, 1670–1672. [Google Scholar] [CrossRef][Green Version]
  45. Yu, D.; Chen, X.-L.; Ai, B.-R.; Zhang, X.-M.; Wang, J.-Y. Tetrabutylammonium iodide catalyzed hydroxylation of naphthoquinone derivatives with tert-butyl hydroperoxide as an oxidant. Tetrahedron Lett. 2018, 59, 3620–3623. [Google Scholar] [CrossRef]
  46. Singh, P.; Natani, K.; Jain, S.; Arya, K.; Dandia, A. Microwave-assisted rapid cyclization of lapachol, a main constituent of Heterophragma adenophyllum. Nat. Prod. Res. 2006, 20, 207–212. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Molecular design of the naphth[1,2-d]imidazoles with anticancer and fluorescent properties.
Figure 1. Molecular design of the naphth[1,2-d]imidazoles with anticancer and fluorescent properties.
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Scheme 1. Synthetic route to obtain the naphth[1,2-d]imidazoles IM1IM7.
Scheme 1. Synthetic route to obtain the naphth[1,2-d]imidazoles IM1IM7.
Molecules 28 03008 sch001
Figure 2. Fluorescence emission spectra of the synthesized naphth[1,2-d]imidazoles (λExc 345 nm).
Figure 2. Fluorescence emission spectra of the synthesized naphth[1,2-d]imidazoles (λExc 345 nm).
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Figure 3. Structural similarity of DAPI and synthesized naphth[1,2-d]imidazoles.
Figure 3. Structural similarity of DAPI and synthesized naphth[1,2-d]imidazoles.
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Table 2. Cytotoxic activity of IM1, IM2, IM4, IM5, IM6, and IM7 after a 72 h exposure expressed by IC50 (µM) and confidence interval.
Table 2. Cytotoxic activity of IM1, IM2, IM4, IM5, IM6, and IM7 after a 72 h exposure expressed by IC50 (µM) and confidence interval.
Cell Line
IC50 (μM) aIC50 (μM) aSI bIC50 (μM) aSI bIC50 (μM) aSI b
NE—not evaluated. a: IC50 is the concentration at which 50% of cells were undergoing cytotoxic cell death due to synthesized compound treatment. b: SI (selectivity index) equals the ratio of IC50 for fibroblasts L929/IC50 for the cancer cell lines.
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Santos, V.L.d.A.; Gonsalves, A.d.A.; Guimarães, D.G.; Simplicio, S.S.; Oliveira, H.P.d.; Ramos, L.P.S.; Costa, M.P.d.; Oliveira, F.d.C.E.d.; Pessoa, C.; Araújo, C.R.M. Naphth[1,2-d]imidazoles Bioactive from β-Lapachone: Fluorescent Probes and Cytotoxic Agents to Cancer Cells. Molecules 2023, 28, 3008.

AMA Style

Santos VLdA, Gonsalves AdA, Guimarães DG, Simplicio SS, Oliveira HPd, Ramos LPS, Costa MPd, Oliveira FdCEd, Pessoa C, Araújo CRM. Naphth[1,2-d]imidazoles Bioactive from β-Lapachone: Fluorescent Probes and Cytotoxic Agents to Cancer Cells. Molecules. 2023; 28(7):3008.

Chicago/Turabian Style

Santos, Victória Laysna dos Anjos, Arlan de Assis Gonsalves, Délis Galvão Guimarães, Sidney Silva Simplicio, Helinando Pequeno de Oliveira, Lara Polyana Silva Ramos, Marcília Pinheiro da Costa, Fátima de Cássia Evangelista de Oliveira, Claudia Pessoa, and Cleônia Roberta Melo Araújo. 2023. "Naphth[1,2-d]imidazoles Bioactive from β-Lapachone: Fluorescent Probes and Cytotoxic Agents to Cancer Cells" Molecules 28, no. 7: 3008.

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