Synthesis of an anthracene-based diguanidine and its recognition of carboxylic acids and phosphonic acids
Graphical abstract
Introduction
The recognition of “oxoacids” and “oxoanions”, such as carboxylic acids (carboxylate) and phosphoric acids (phosphate) with artificial receptors, is of particular interest due to their applications in the chemical, biological and environmental sciences [1]. Although there are numerous reports of synthetic receptors for the recognition of “carboxylate anions”, the receptors for the recognition of “carboxylic acids” are relatively rare [1](a), [1](b). Additionally, the synthetic receptors for the “phosphonic acids” are also quite rare compared to the recognition of “phosphoric acids”. Only a few examples of synthetic receptors for the recognition of the phosphonic acids have been reported [2].
On the other hand, the amidino group (amidine) [3] and guanidyl group (guanidine) [4] have become extremely advantageous functional groups for the binding of oxoacids. Recently, we reported that the synthesis of anthracene-based “diamidine”, which recognizes dicarboxylic acids, mono phosphonic acids and diphosphonic acid derivatives as a turn-on fluorescence sensor [2](c), [3](f). To explore the applicability of these functional receptors for the recognition of oxoacids, we have synthesized the new anthracene-based diguanidine 1 (Chart 1).
The anthracene-based diguanidine 1 was synthesized according to two types of procedures from the 1,8-diaminoanthracene including the use of Goodman’s reagent [5] for the synthesis of a Boc-protected diguanidine, and also applied the use of an ion-exchange resin for the neutralization of the guanidine hydrochloride to the target diguanidine 1. The obtained diguanidine 1 recognized dicarboxylic acids, diphosphonic acids and methylphosphonic acid in a DMSO solution, and the formation of 1:1 and 1:2 complexes was determined by a DOSY NMR analysis. The yellow fluorescence of the diguanidine 1 turns off the fluorescence after the addition of dicarboxylic acids. However, for the recognition of phosphonic acid derivatives, the fluorescence color turned purple due to the formation of binding complexes. The yellow fluorescence of the diguanidine 1 may come from the weak aggregation state of 1 which was estimated by concentration-dependent fluorescence studies.
Section snippets
Synthesis of diguanidine 1
The anthracene-based diguanidine 1 was prepared according to Scheme 1. In the first synthetic route, the anthracene-based diguanidine dihydrochloride 1•2HCl was prepared from the reaction of 1,8-diaminoanthracene and the cyanamide under acidic conditions (HCl/EtOH) [6]. In this synthetic route, the diguanidine dihydrochloride 1•2HCl must be obtained using sequential precipitation by the addition of AcOEt-hexane mixed solvents from the high viscosity dark brown reaction mixture. To obtain pure
Conclusions
We have synthesized the anthracene-based diguanidine 1 for the recognition of carboxylic acids and phosphonic acids. The diguanidine 1 was synthesized using two types of synthetic routes including the application of Goodman’s reagent, and also applied a basic ion-exchange resin for the neutralization of the diguanidine hydrochloride to the target diguanidine 1. The diguanidine 1 forms 1:1 complexes with dicarboxylic acids 3, 4, 6c-6e (n = 5–7) in a DMSO solution and the formation of the
General methods
The 1H NMR and 13C NMR spectra were recorded using Avance III 500 (500 and 125 MHz) spectrometers. The FAB-mass spectra were recorded by a JEOL JMS-700 mass spectrometer. The absorption spectra were recorded by a SHIMADZU UV-2550 UV–Visible spectrometer. The fluorescence spectra were recorded by a JASCO FP-6200 spectrometer, and the fluorescence spectra were corrected using rhodamine B as the reference. All solvents and reagents were purified according to standard procedures. For the
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was supported by KAKENHI (18K04634) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.
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