Azacalixphyrins as NIR photoacoustic contrast agents

Lavaud, Lucien; Pascal, Simon; Metwally, Khaled; Gasteau, Damien; Silva, Anabela Da; Chen, Zhongrui; Elhabiri, Mourad; Canard, Gabriel; Jacquemin, Denis; Siri, Olivier

doi:10.1039/c8cc05851b

Cited by 15 publications

(27 citation statements)

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“…We have further performed theoretical calculations to help rationalizing the obtained results, computational details can be found in the ESI †. As for the previously-studied monomeric 1-3, 13,15,16,17 we could find several almost iso-energetic tautomers for the neutral form of 4 represented in Fig. 1 depending on the relative positions of the imine and amine groups.…”

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confidence: 66%

“…The synthesis of the key intermediate bis-azacalixarene 10 was envisaged either from the reactive tetraaminobenzene derivatives 5a or 5b that feature a good air-stability when stored as di-hydrochloride salts (Scheme 1). Using a synthetic pathway similar to the one allowing the preparation of N-substituted azacalixphyrins (2 and 3), 17 the adduct 7 was produced by the Nuleophilic Aromatic Substitution (SNAr) of the N,N-dioctyl tetraaminobenzene hydrochloride 5a on two equivalents of 1,3-difluroro-4,6-dinitrobenzne 6 in the presence of N,N-diisopropylethylamine (DIPEA). Despite investigating multiple experimental conditions, the subsequent SNAr between two equivalents of 7 and one equivalent of the unsubstituted tetraaminobenzene 5b afforded only the bis-N-octylazacalixarene 8, that is produced with a high yield of 90% from an equimolar mixture of the starting derivatives.…”

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Fused bis-azacalixphyrin that reaches NIR-II absorptions

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confidence: 66%

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Fused bis-azacalixphyrin that reaches NIR-II absorptions

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“…20 Next, the Nfunctionalization with aryl substituents, such as in 1aa, enabled to obtain bathochromic and hyperchromic shifts with absorption beyond 900 nm. 21 To date, ACPs have been identified as photoacoustic imaging probes upon NIR excitation, and the absorption of this family of dyes has been very recently extended to the second transparency window (NIR-II), i.e., beyond 1000 nm thanks to a fused ACP dimer. 21,22 Alongside these achievements, theoretical investigations allowed to predict NIR absorptions for metallated or C-substituted ACPs, 23,24 although such structures remain to be synthesized.…”

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confidence: 99%

MixedN-aryl/alkyl substitution favours an unusual tautomer of near-infrared absorbing azacalixphyrins

et al. 2020

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“…900 nm that can be tuned by substitution of the peripheral imine functions (Figure 1, R = H, aryl, alkyl). 30,34 Chart 1. Scope of the study (only the canonical form is represented).…”

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confidence: 99%

“…All H-atoms were found experimentally for 2a and 3a, except the one for amine N6 in ously reported crystal structure of 1a, featuring a zwitterionic ground state, single and double bonds in both subunits of the quinoidal ring (BLA electron-donating aromatic substituents in which helps to rationalize the optical properties of ACQ experimental evidences that aryl-substituted ACPs tend to st tion brought by the aryl substituents. 31,34…”

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Azacalixquinarenes: From Canonical to (Poly-)Zwitterionic Macrocycles

et al. 2019

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Azacalixquinarenes, a new family of macrocycles constituted of diaminobenzoquinone diimine units linked by dinitrobenzene rings are synthesized by selected oxidation of the parent azacalixarenes. Crystallographic analyses of two compounds demonstrated the presence of (uncharged) canonical and zwitterionic quinones within a single structure. The electron-withdrawing nature of the dinitrobenzene moieties can trigger the intramolecular H-transfer that generates zwitterionic-ground state quinones. The nature of the Nsubstituents and the polarity of the solvent have a crucial impact on the equilibrium between the canonical and zwitterionic forms that present distinct optical and electrochemical properties. Thus, within [4]-and [6]-membered macrocycles, poly-zwitterionic structures can be reached, as demonstrated experimentally and theoretically using first-principle approaches. With the aim to combine several of these systems in a single molecule and study the impact on the canonical/zwitterionic equilibrium, we naturally focused our attention on the elaboration of macrocyclic architectures of types 2 or 3 presenting an alternation of quinones and aromatic rings substituted with EWG. We report herein their synthesis from ACA precursors and demonstrate that these macrocycles (2a-c and 3a), named azacalixquinarenes (ACQ), can be seen as "hemi-azacalixphyrins", i.e. an intermediary class of ACA-ACP derivatives featuring an alternation of dinitrosubstituted aromatic rings and diaminobenzoquinone diimine rings. As for model compounds 1a-d, the quinoidal fragments within ACQs can be either stabilized under canonical (uncharged) or zwitterionic forms depending on given parameters (N-substituents, solvent), allowing to reach unprecedented poly-zwitterionic systems. RESULTS AND DISCUSSION Synthesis. The access to the target ACQs 2a-c was envisaged by chemical oxidation of the azacalix[4]arene precursors (Scheme 1). Therefore, the preparation of ACA 7a-c was carried out following a well-established strategy starting from precursors 4a-c, incorporating octylamine or selected aniline moieties, which were reduced under acidic conditions in presence of Sn(II) salts or Fe powder, then substituted by 1,5-difluoro-2,4-dinitrobenzene (DFDNB) to afford the adducts 6a-c. 30, 34 Scheme 1. Synthesis of compounds 1a-d, 2a-c and 3a (quinones only represented under their canonical forms). These intermediates were converted to the corresponding azacalix[4]arene 7a-c using one equivalent of tetraaminobenzenes 4a-c in refluxing acetonitrile. For compound 6d, previously unknown, the reaction was carried out at room temperature and a low concentration of 5d (10-2 M) was necessary to reach a moderate yield (43%, Table S1). Such poor efficiency is presumably imputable to a lack of regioselectivity during the nucleophilic aromatic substitution of the electron-rich adduct 5d on DFDNB. Unfortunately, for the same reason, it was impossible to reach the corresponding azacalix[4]arene 6d using classical conditions. The synthesis of azacalix[6]arenes 8a wa...

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Azacalixphyrins as NIR photoacoustic contrast agents

Abstract: Newly designed aryl-substituted azacalixphyrins are promising contrast agents for photoacoustic imaging upon excitation in the 800–1000 nm NIR range.

Cited by 15 publications

References 39 publications

Fused bis-azacalixphyrin that reaches NIR-II absorptions

Fused bis-azacalixphyrin that reaches NIR-II absorptions

MixedN-aryl/alkyl substitution favours an unusual tautomer of near-infrared absorbing azacalixphyrins

Azacalixquinarenes: From Canonical to (Poly-)Zwitterionic Macrocycles

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