Chiral recognizable host–guest interactions detected by fast-atom bombardment mass spectrometry: application to the enantiomeric excess determination of primary amines

Eur. J. Mass Spectrom. 7, 447–459 (2001)
DOI: 10.1255/ejms.460

Chiral recognizable host–guest interactions detected by fast-atom bombardment mass spectrometry: application to the enantiomeric excess determination of primary amines

Masami Sawada,^* Yoshio Takai, Hiroyuki Imamura, Hitoshi Yamada and Shigetoshi Takahashi
The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Hiroshi Yamaoka
Faculty of Science, Osaka Women’s University, Sakai, Osaka 567-0035, Japan
Keiji Hirose and Yoshito Tobe
Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Jyuichi Tanaka
Faculty of Engineering, Osaka Institute of Technology, Asahi-ku, Osaka 535-0002, Japan

ABSTRACT:

The enantiomeric excess (ee) of organic amine compounds has been determined using fast-atom bombardment (FAB) mass spectrometry based on the chiral host–guest complexation systems. The method uses a 1 : 1 mixture of the given chiral crown ether hosts (H_RRRR and H_SSSS-dn), one of whose enantiomers is isotopically labeled, for the ee– determination of a given amine salt guest (G⁺). The peak intensity ratio {I[(H_RRRR + G)⁺] / I[(H_SSSS-dn + G)⁺] = IRIS} of the two diastereomeric host–guest complex ions clearly changes with the change in the ee of the guest. The intensity excess (I_e) of the two complex ion peaks is newly defined as I_e = (IRIS – 1) / (IRIS + 1). The two sets of mass spectrometrically obtained I_e values vs a set of ee values of phenylalanine methyl ester and leucine methyl ester hydrochlorides show excellent linear relationships through the zero point (R² = 0.9989 and R² = 0.9970, respectively). This indicates the potential utility of the present ee– determination method to within ± 3% ee. Furthermore, based on the solution equilibrium distributions of the complex ions, the linearity is mathematically justified. Therefore, the ee-determination can be simplified as ee (%) = (|I_e| / |I_e(100)|) × 100: here, I_e(100) is the corresponding I_e value obtained using an enantiomerically pure (100% ee) guest as a reference. The present chiral dimethoxyphenyl crown ether host pairs employed are effective (IRIS ³ 1.5) for the ee-determination of most a-amino acid esters, but not effective (IRIS » 1.0) for most simple alkylamines.

Keywords: chiral recognition, enantiomeric excess, host–guest complexation, chiral crown ether, fast-atom bombardment, deuterium labeling

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