Molecules 2001, 6, M219 http://www.mdpi.org/molbank/m0219.htm 1 / 2 4/21/2008 3:34 PM Molecules 2001, 6, M219 2-Bromo-3-ethylthiazolium Tetrafluoroborate (BET) Györgyi Kovács 1* , Zoltán Kele 1 , Péter Forgó 2 and Lajos Kovács 1 1. Department of Medicinal Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary. Phone: +36 62 54 51 45 , Fax: +36 62 54 59 71, * E-mail: gyorgyi@ovrisc.mdche.u-szeged.hu 2. Department of Organic Chemistry , University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary Received: 20 January 2001 / Accepted: 15 May 2001 / Published: 25 May 2001 Recent progress in peptide synthesis resulted in the elaboration of novel coupling agents. One successful approach involves the application of thiazolium salts, e.g. 2-bromo-3-ethyl-4-methylthiazolium tetrafluoroborate (BEMT) [1-3]. This compound can be prepared from 2-bromo-3-ethyl-4-methylthiazole [1, 2]. We have found that a simpler analogue, 2-bromo-3-ethylthiazolium tetrafluoroborate (BET), can be prepared in convenient steps from the commercially available 2-aminothiazole using the procedure by Dondoni et al. [4] to obtain 2-bromothiazole which, in turn, was readily transformed into the title compound. In our experience BET is a highly efficient coupling reagent in the synthesis of peptide nucleic acid (PNA) oligomers in solution phase. To a stirred solution of 2-bromothiazole [4] (1.78 mL, 20.0 mmol) in 1,2-dichloroethane (DCE, 20 mL) the solution of triethyloxonium tetrafluoroborate (11.4 g, 60.0 mmol) in DCE(60 mL) was added over 45 min. at 80 °C. When the reaction was complete (16 h) according to TLC (n-buthanol : acetic acid : water = 4:1:1) the solution was concentrated in vacuo. After the residue was precipitated from diethyl ether it was recrystallized from abs. acetonitrile/ethyl acetate to afford white plates. Yield: 4.48 g (80 %). Mp: 137.9-139.2 °C. 1 H NMR (DMSO-d 6 , 500 MHz, δ, ppm): 1.47 (t, J = 7.0 Hz, 3H, CH 2 CH 3 ); 4.52 (q, J = 7.0 Hz, 2H, CH 2 CH 3 ); 8.35 (d, J = 4.1 Hz, 1H, aryl); 8.56 (d, J = 4.1 Hz, 1H, aryl). 13 C NMR (DMSO-d 6 , 125 MHz, δ, ppm): 14.19 (CH 2 CH 3 ); 50.61 (CH 2 CH 3 ); 127.45 (C-5); 137.73 (C-4); 146.50 (C-2). ESI-MS (m/z, %): 191.8 (100, [C 5 H 7 79 BrNS] + ); 193.8 (97, [C 5 H 7 81 BrNS] + ). Anal. cald. for C 5 H 7 BBrF 4 NS (279.891): C, 21.45; H, 2.52; Br, 28.55; F, 27.15; N, 5.00; S, 11.46; found C, 21.47; H, 2.51; Br, 28.52; F, 27.20; N, 5.01; S, 11.44. References 1. Li, P.; Xu, J. C. Tetrahedron Lett.1999, 40, 8301-8304. 2. Li, P.; Xu, J. C. J. Org. Chem. 2000, 65, 2951-2958. 3. Li, P.; Xu, J. C. Tetrahedron 2000, 56, 8119-8131. 4. Dondoni, A. in Modern synthetic methods; Scheffold, R., Ed.; Verlag Helvetica Chimica Acta & Verlag Chemie: Basel, Weinheim, New York, Cambridge, 1992; Vol. 6, p 385. Sample availability: sample available from the authors and MDPI.