An acenaphthopyrrolone-dipicolylamine derivative as a selective and sensitive chemosensor for group IIB cations Ali Coskun, M. Deniz Yilmaz and Engin U. Akkaya * Department of Chemistry, Middle East Technical University, Ankara TR-06531, Turkey Received 2 January 2006; revised 17 March 2006; accepted 22 March 2006 Available online 17 April 2006 Abstract—The recently reported acenaphthopyrrolone (ACNP) class of fluorophores have remarkably bright emission in the red end of the visible spectrum. We demonstrated that straightforward derivatization with 2-aminoethyl-dipicolylamine yields a selective and sensitive chemosensor for Zn(II), Cd(II) and Hg(II) ions. Further modifications could result in water-soluble derivatives, with practical applications in intracellular imaging of Zn(II) concentrations. Ó 2006 Elsevier Ltd. All rights reserved. Selective sensing and signalling of metal ions is an attractive goal considering the biological and environ- mental implications. 1 Metal ions, such as Cd(II) and Hg(II), are environmental pollutants, and Zn(II) is involved in a number of biological processes like Alzhei- mer’s, 2 and diabetes 3 and in the plant kingdom in a large number of regulatory processes. 4 Regulation of zinc uptake has been linked to human prostate cancer in a recent study. 5 Therefore, sensing and preferential visualization of these ions is of prime importance. 6 As a research group involved in chemosensor design, 7 we are also very interested in the application of novel fluo- rophores in this field. Thus, a recently reported fluoro- phore, 8 acenaphthopyrrolone derivative 1 attracted our attention. These acenaphthopyrrolone dyes were shown to emit in the red region of the spectrum (610 nm) with good quantum yields and very good opportunities for straightforward derivatization. The skeletal structure is highly electron deficient, and nucleophilic aromatic substitution is very favorable. Acenaphthopyrrolone dyes can be obtained in two steps from commercially available precursors with some improvements on the literature procedure. 8 Thus, acenaphthaquinone was reacted with malononitrile in aceto- nitrile at reflux overnight. On cooling to room temperature, the precipitated material was collected by filtration. The intermediate compound was not further purified, but directly transformed into compound 1 by refluxing in acetonitrile in the presence of a catalytic amount of anhydrous K 2 CO 3 . As the ligand to tether to the core, we chose a very common structural motif 2, which is used in a large number of zinc chemosen- sors, 9 derived from dipicolylamine (DPA). The addition of an aminoethyl moiety to DPA is expected to increase the binding, affinity and supply a primary amine for nucleophilic substitution of the core. The target chemosensor 3 was synthesized by the over- night reaction of 2-aminoethyl-dipicolylamine with compound 1 in acetonitrile at room temperature. The reaction product was purified by silica gel column chro- matography (CHCl 3 –MeOH, 85:15). Satisfactory ana- lytical data was obtained for compound 3, which was in accord with the expected structure. 10 The absorption spectrum of compound 3 in acetonitrile is shown in Figure 1. The spectrum shows one peak in N O NC H 2 N N N N CH 3 CN, rt, 24h N O NC NH N N N 1 2 3 0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2006.03.128 * Corresponding author. Tel.: +90 312 210 5126; fax: +90 312 210 1280; e-mail: akkayaeu@metu.edu.tr Tetrahedron Letters 47 (2006) 3689–3691