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. 2021 Mar 22;26(6):1788.
doi: 10.3390/molecules26061788.

Solution and Solid State Studies of Urea Derivatives of DITIPIRAM Acting as Powerful Anion Receptors

Patryk Niedbała  1 , Kajetan Dąbrowa  1 , Agnieszka Cholewiak-Janusz  1 , Janusz Jurczak  1
Affiliations

Solution and Solid State Studies of Urea Derivatives of DITIPIRAM Acting as Powerful Anion Receptors

Patryk Niedbała et al. Molecules. .

Abstract

Herein, we present the synthesis and anion binding studies of a family of homologous molecular receptors 4-7 based on a DITIPIRAM (8-propyldithieno-[3,2-b:2',3'-e]-pyridine-3,5-di-amine) platform decorated with various urea para-phenyl substituents (NO2, F, CF3, and Me). Solution, X-ray, and DFT studies reveal that the presented host-guest system offers a convergent array of four urea NH hydrogen bond donors to anions allowing the formation of remarkably stable complexes with carboxylates (acetate, benzoate) and chloride anions in solution, even in competitive solvent mixtures such as DMSO-d6/H2O 99.5/0.5 (v/v) and DMSO-d3/MeOH-d3 9:1 (v/v). The most effective derivatives among the series turned out to be receptors 5 and 6 containing electron-withdrawing F- and -CF3para-substituents, respectively.

Keywords: DITIPIRAM; acyclic receptors; anion recognition; supramolecular chemistry.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Structure of the 8-propyldithieno [3,2-b:2′,3′-e]pyridine-3,5-diamine (DITIPIRAM) platform.
Figure 2
Figure 2
Structures of receptors 2 and 3.
Scheme 1
Scheme 1
Synthesis of acyclic receptors 4–7 varying in para-substituent (R) on the aryl rings.
Figure 3
Figure 3
Representative comparison of chemical shift changes (Δδ) for urea protons NH(2/2′) (a) and NH(3/3′) (b) upon addition of TBA+X– (Cl−, PhCO2−, MeCO2−) to the solution of 6 in DMSO-d6 + 0.5% H2O (closed symbols) and DMSO-d6 + 10% CD3OH (open symbols); fitted binding isotherms (gray lines).
Figure 4
Figure 4
X-ray structures of 6@(DMSO∙H2O) solvate (a,c) and the 6@(Cl)TBA anionic complex (b,d). Non-acidic protons and disorder were omitted for clarity; the hydrogen bonds are shown as dashed blue lines. For hydrogen bond lengths (a–d), see the inset table in Figure 5.
Figure 5
Figure 5
Geometrical descriptors of the binding pocket of the DITIPIRAM-based receptor 6 (a), superposition of crystal structures of 6∙(DMSO∙H2O) solvate (colored in blue) and 6∙TBACl (colored in green) (b).
Figure 6
Figure 6
Superposition of DFT-calculated structures of receptors 2−7 and their complexes with chloride, acetate, and benzoate exemplifies the high preorganization of the DITIPIRAM moiety (a) and average values of geometrical parameters describing anion complexes (b); see Figure 5a for labels.
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