title: Differentiation of diasteromeric α-sulfanyl-β-amino acid derivatives by electrospray ionization tandem mass spectrometry.
abstract: A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.
authors.affiliation: National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad 500 007, India.
authors.forename: Gundimeda S
authors.initials: GS
authors.lastname: Ramanjaneyulu
authors.forename: Davalagar Vijay
authors.initials: DV
authors.lastname: Darshan
authors.forename: Koosam
authors.initials: K
authors.lastname: Mahendar
authors.forename: Mannepalli Lakshmi
authors.initials: ML
authors.lastname: Kantam
authors.forename: Sripadi
authors.initials: S
authors.lastname: Prabhakar
mesh_terms: D000596:Amino Acids / Q000032:analysis* / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids