Benzothiadiazoyl-triazoyl cyclodextrin: a selective fluoroionophore for Ni(II) Stephane Maisonneuve a , Qiang Fang b , Juan Xie a, * a PPSM, Institut d’Alembert, ENS Cachan, CNRS, UniverSud, 61 av President Wilson, F-94230 CACHAN, France b Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China article info Article history: Received 7 May 2008 Received in revised form 20 June 2008 Accepted 26 June 2008 Available online 1 July 2008 Keywords: Cyclodextrin One-pot click chemistry Benzothiadiazole Ni(II) Fluoroionophore Multichromophoric system abstract A new multichromophoric cyclodextrin substituted with benzothiadiazoyl-triazole moiety has been synthesized by a one-pot click reaction between azido-cyclodextrin and TMS-ethynyl benzothiadiazole in the presence of TBAF. This fluorescent chemosensor exhibits a high selectivity to Ni 2þ among a series of cations in CH 3 CN solution. The association constant for the 1:1 complex was determined to be 2.8810 7 M 1 . Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, considerable efforts have been devoted to the design and synthesis of molecular sensors for the analytical de- tection of environmentally and biologically relevant metal ions. 1 Nickel is an essential element to plants and many other biota and able to form complex with amino acids, peptides, phosphates, nu- cleotides, and nucleic acids. 2 It is implicated in various enzyme activities such as ureases, hydrogenases, superoxide dismutases, acireductone dioxygenases, acetyl-coenzyme A synthases, carbon monoxide dehydrogenases, and methyl-coenzyme M reductases, 2 and frequently used in catalytic processes. However, as an in- dustrial pollutant, nickel is a toxic element that can cause lung injury, allergy, and carcinogenesis. Selective monitoring of Ni 2þ in industrial, environmental, and food samples is, therefore, needed. Up to date, most of Ni 2þ -selective sensors are based on potentio- metric methods. 3 Several Ni 2þ -sensitive fluorescent sensors have been reported but there are serious interferences from other transition metal ions like Cu 2þ , Pb 2þ , Zn 2þ , and Fe 2þ . 4 As a con- tinuing program on the design and synthesis of sugar-derived macrocycles possessing complexing properties, 5 we are particu- larly interested in the functionalization of cyclodextrins. 6 Using click chemistry, 7 we have prepared 2-pyridyl-triazole substituted b-cyclodextrins as Zn 2þ -sensitive fluorescent chelating agents, where pyridyl-triazole was designed for ion coordination. The co- ordination properties of 1,2,3-triazoles encouraged us to explore other triazole-heterocycle conjugates as potential fluo- roionophores. 8 Recently, benzothiadiazole derivatives have been used in the development of organic light-emitting materials and devices, thanks to their high fluorescence efficiency. 9 Furthermore, thiadiazole has been used as metal binding site. 10 We then decided to functionalize the b-cyclodextrin with benzothiadiazoyl-triazole to investigate their potential as novel fluorescent sensors. 2. Results and discussion We have first realized the synthesis of benzothiadiazoyl-triazole appended methyl glucopyranoside 4 (as the model compound) and b-cyclodextrin 6 (Scheme 1). Sonogashira coupling of 4-bromo- 2,1,3-benzothiadiazole 1 with trimethylsilylethyne afforded TMS- ethynyl benzothiadiazole 2. We found that this TMS protected alkyne derivative can be directly used for the Huisgen 1,3-dipolar cycloaddition with methyl 6-azido-6-deoxy-2,3,4-tri-O-acetyl-a-D- glucopyranoside 3 or acetyl protected per-(6-azido)-b-CD 5 6 in the presence of a CuSO 4 /ascorbate mixture and TBAF for in situ deprotection of TMS group (Scheme 1). It is to be noted that direct use of silylated alkyne as the Huisgen cycloaddition partner in the presence of TBAF has never been reported before. Synthesis of triazole derivative by direct use of TMS-alkyne has been recently reported with the one-pot Ag(I)-mediated deprotection. 11 In situ desilylation of TMS-alkyne under basic conditions has been de- scribed with the formation of bis-triazole as the major compound. 12 * Corresponding author. Tel.: þ33 1 47405586; fax: þ33 1 47402454. E-mail address: joanne.xie@ppsm.ens-cachan.fr (J. Xie). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2008.06.102 Tetrahedron 64 (2008) 8716–8720