Quantitative Chiral Analysis of Sugars by Electrospray Ionization Tandem Mass Spectrometry Using Modified Amino Acids as Chiral Reference Compounds D. V. Augusti, ². ⊥ F. Carazza, ‡ R. Augusti, ², ⊥ W. A. Tao, §,⊥ and R. G. Cooks* ,⊥ Departamento de Quı ´ mica, Universidade Federal de Minas Gerais, Belo Horizonte/MG, Brazil 31270-901, and Department of Chemistry, Purdue University, West Lafayette, Indiana 47907 Rapid quantitative enantiomeric analysis of mannose, glucose, galactose, and ribose is achieved using electro- spray ionization and cluster ion dissociation with data analysis by the kinetic method. Several modified amino acids (N-Ac-L-Phe, N-benzoyl-L-Phe, N-t-Boc-L-Phe, N-Ac- L-Pro, N-t-Boc- L-Pro, N-Fmoc-L-Pro, N-Ac-L-Tyr, O-Me- L-Tyr) and four transition divalent metal cations (Co 2 + , Cu 2 + , Ni 2 + , and Zn 2 + ) were tested to select the best system for chiral recognition and quantitation of each sugar. Quantitative determinations of the enantiomeric composi- tions of sugar solutions were achieved using either multiple- or two-point calibration curves; differences between the actual and experimental values were <2% enantiomeric excess (ee). Significant progress has been made during the past few years on chiral identification and quantification 1-3 based exclusively on mass spectrometry. It is possible to classify the mass spectrometry methods used for chiral recognition and quantification into four types: (1) Host -guest diasteromeric adducts are generated using a chiral guest and analyzed in a single-stage mass spectrometer in the first type of experiment. One of the enantiomeric hosts is isotopically labeled, and thus, the corresponding mixture of diasteromeric adducts can be mass-resolved. Chemical ioniza- tion, 4,5 fast atom bombardment (FAB), 6-8 matrix-assisted laser desorption/ ionization (MALDI), 9 and electrospray ionization (ESI) 10 mass spectrometry have all been used in this type of experiment. (2) Chiral recognition in the second type of experiment is based on ion/ molecule reactions. 11 Diasteromeric adducts, gen- erated by inserting the analyte into a chiral host molecule, are mass-selected and allowed to react with a neutral reagent that need not be chiral. Chiral distinction is possible, since the rates of guest exchange depend on the chirality of the enantiomeric guest. 12-15 (3) A third group of methods for chiral recognition is based on collision-induced dissociation (CID) of diasteromeric adducts in a tandem mass spectrometry (MS/ MS) experiment. 16-19 (4) A fourth approach uses tandem mass spectrometry and the kinetic method to quantify chiral effects. 20-22 This methodology has been successfully applied to quantitative analysis of amino acids, 23,24 R-hydroxyacids 25 and some drugs. 26,27 It is the subject of the present study. * Corresponding author. Tel: (765) 494-5262. Fax: (765) 494-0239. E-mail: cooks@ purdue.edu. † On leave from Departamento de Quı ´mica, Universidade Federal de Minas Gerais, Belo Horizonte/ MG, Brazil 31270-901. ‡ Universidade Federal de Minas Gerais. § Current address: The Institute for Systems Biology, 1441 N. 34th St., Seattle, WA 98103. ⊥ Purdue University. (1) Guo, J.; Wu, J.; Siuzdak, G.; Finn, M. G. 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