title: Differentiation of a pair of diastereomeric tertiarybutoxycarbonylprolylproline ethyl esters by collision-induced dissociation of sodium adduct ions in electrospray ionization mass spectrometry and evidence for chiral recognition by ab initio molecular orbital calculations.
abstract: The fragmentation of the sodium adduct ions for tert-butoxycarbonyl-L-prolyl-L-proline ethyl ester (Boc-L-Pro-L-Pro-OEt) was compared with that for Boc-D-Pro-L-Pro-OEt in positive-ion electrospray ionization (ESI) mass spectrometry. In the collision-induced dissociation (CID) mass spectra of the [M + Na](+) ions, the abundance of the [M + Na - C(CH(3))(3) + H](+) ion, which is due to the loss of a tert-butyl group from the [M + Na](+) ion for Boc-D-Pro-L-Pro-OEt, was about eight times higher than that for Boc-L-Pro-L-Pro-OEt. In addition, in the CID spectra of the sodium adduct fragment ion ([M + Na - Boc + H](+)), the abundance of the [M + Na - Boc - prolylresidue + H](+) ion, which is due to the loss of prolyl residue from the [M + Na - Boc + H](+) ion for Boc-L-Pro-L-Pro-OEt, was about five times higher than that for Boc-D-Pro-L-Pro-OEt. These results indicate that Boc-L-Pro-L-Pro-OEt was distinguished from Boc-D-Pro-L-Pro-OEt by the CID mass spectra of the sodium adduct ions in ESI mass spectrometry. The optimized geometries of the [M + Na](+) and the [M + Na - Boc + H](+) ions calculated by ab initio molecular orbital calculations suggest that the chiral recognition of these diastereomers was due to the difference of the orientation of a sodium ion to the oxygen and nitrogen atoms in dipeptide derivatives, and to the difference of the total energies between them.
authors.affiliation: Faculty of Pharmaceutical Sciences, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan. tsunemat@fukuoka-u.ac.jp
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tsunematsu
authors.forename: Hirohito
authors.initials: H
authors.lastname: Ikeda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hanazono
authors.forename: Masanori
authors.initials: M
authors.lastname: Inagaki
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Isobe
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Higuchi
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Goto
authors.forename: Magobei
authors.initials: M
authors.lastname: Yamamoto
mesh_terms: D004151:Dipeptides / Q000737:chemistry*; D004952:Esters; D007477:Ions / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D012964:Sodium / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
chemical_list: D004151:Dipeptides; D004952:Esters; D007477:Ions; C448039:prolyl-proline; D012964:Sodium