Study of the Fragmentation of 3(2H)-Furanones by Mass Spectrometry L. B. Fay, T. Huynh-Ba, and I. Blank* Nestle ´ Research Centre, Nestec Ltd., Vers-chez-les-Blanc, P.O. Box 44, 1000 Lausanne 26, Switzerland Fragmentation of 4-hydroxy-5-methyl-3(2H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and 2(or 5)-ethyl-4-hydroxy-5(or 2)-methyl-3(2H)-furanone was studied by gas chromatography/mass spectrometry and by gas chromatography/tandem mass spectrometry. Experiments were carried out using unlabeled reference compounds and isotopically labeled molecules. The latter were obtained either by synthesis or through the Maillard reaction based on xylose and alanine or glycine. A general fragmentation pathway of alkylated 4-hydroxy-3(2H)-furanones is proposed on the basis of cross-examination of the mass spectrometric data obtained from these different compounds. Keywords: 4-Hydroxy-2,5-dimethyl-3(2H)-furanone; 4-hydroxy-5-methyl-3(2H)-furanone; 2(or 5)- ethyl-4-hydroxy-5(or 2)-methyl-3(2H)-furanone; mass spectrometry; GC/MS/MS; fragmentation; Maillard reaction; pentose INTRODUCTION Mass spectrometry, particularly in combination with gas chromatography (GC/MS), is one of the most widely used tools in food analysis. The success of this tech- nique for compound identification is largely due to its sensitivity and also to the availability of mass spectral libraries that help to identify unknown compounds. However, an unknown compound can be identified even if its spectrum has not yet been registered in a library. In such a case, its identification can be achieved if the fragmentation pathways of similar molecules are known. Moreover, the fragmentation pathways of compounds allow study of their formation mechanisms when using isotopically labeled precursors (Tressl et al., 1993). 3(2H)-Furanones are important compounds contribut- ing to the flavor of many natural products and thermally processed foods. 4-Hydroxy-2,5-dimethyl-3(2H)-fura- none (Furaneol, 1), 2(or 5)-ethyl-4-hydroxy-5(or 2)-meth- yl-3(2H)-furanone (homofuraneol, 2), and 4-hydroxy-5- methyl-3(2H)-furanone (norfuraneol, 3) have been identified in foods and food-related model systems (Hodge et al., 1963; Nunomura et al., 1976; Severin and Seilmeier, 1967). Alkylated 4-hydroxy-3(2H)-furanones exist in the tautomeric forms I and II (Scheme 1). Tautomeric ratios from 1:2 (Re et al., 1973) to 1:3 (Huber, 1992) have been reported for the homofuraneol tautomers 2A and 2B (R ) C 2 H 5 ). The tautomers of 2 can be separated by GC on polar stationary phases (Blank and Fay, 1996; Blank et al., 1997). In contrast, Furaneol tautomers cannot be distinguished due to symmetry of the molecule. The mass spectra of 1-3 were first published by Rodin et al. (1965), Re et al. (1973), and Tonsbeek et al. (1968), respectively. However, a complete description of their fragmentation is not yet available. To the best of our knowledge, only a few attempts have been made to interpret the fragmentation of 3(2H)-furanones. Some authors discussed a few fragments generated with conventional GC/MS with electron impact ionization (Nunomura et al., 1976; Preininger and Grosch, 1994). However, no systematic studies have yet been pub- lished. In contrast, fragmentation of isotetronic acids [3-hydroxy-2(5H)-furanones] and the corresponding meth- yl esters has been extensively studied by Bonini et al. (1980, 1981). Recently, we discussed formation of Furaneol and homofuraneol through the Maillard reaction based on pentose sugars (Blank and Fay, 1996). Using isotopi- cally labeled precursors, a mechanism for the formation of 3(2H)-furanones via Strecker-assisted chain elonga- tion of the pentose moiety was proposed on the basis of data obtained by GC coupled with tandem mass spec- trometry (GC/MS/MS). However, 3(2H)-furanones, par- ticularly Furaneol, can also be generated by condensa- tion of sugar fragmentation products (Blank et al., 1996). We report here on the mass spectrometric fragmenta- tion of 3(2H)-furanones, which has been established using synthesized isotopically labeled analogues. In addition to GC/MS, GC/MS/MS was used because of its suitability for mechanistic studies (Fay et al., 1996). The proposed fragmentation schemes were applied to isoto- pomers of 3(2H)-furanones formed in Maillard model reactions. MATERIALS AND METHODS The following nomenclature was used (A Guide to IUPAC. Nomenclature of Organic Compounds, recommendation 1993; Blackwell Scientific Publications: Oxford, U.K., 1993): 2-([2,2,2- * Author to whom correspondence should be ad- dressed (fax +41/21-785-86-07; e-mail imre.blank@ chlsnr.nestrd.ch). Scheme 1. Tautomerization of Alkylated 4-Hydroxy-3(2H)-furanones Resulting in the Tautomeric Forms A and B (R ) CH3 for Furaneol and R ) C2H5 for Homofuraneol) 4057 J. Agric. Food Chem. 1997, 45, 4057-4064 S0021-8561(97)00230-6 CCC: $14.00 © 1997 American Chemical Society