Chiral recognition and enantiomer assays of N-(3,5-dinitrobenzoyl)amino acid derivatives using electrospray ionization–mass spectrometry

Enantiomer assays of amino acid derivatives using tertiary amine appended trans-4-hydroxyproline derivatives as chiral selectors in the gas phase

“…150 • C, cone voltage 8 V, capillary voltage 3.5 kV, syringe pump 5 L min −1 , desolvation gas flow 408 L h −1 , and cone gas flow 60 L h −1 . observed in the ESI-mass spectrum, the˛M S values were greater than those observed using proline-based chiral selectors, (S)-2 and (R)-3 [57]. Also, the sense of chiral recognition is consistent with what is observed previously ( Table 2).…”

“…(1) is used to determine X R . However, the observed˛M S value of (2S, 4R)-4 and (2R, 4S)-5 for analyte 8 is much diminished, compared to proline-based selectors (S)-2 and (R)-3 [57], although intensities of selector-analyte complexes are relatively increased. The enantioselectivities are also less for diethyl amide of DNB-leucine, 9 and DNB-leucine, 10, respectively.…”

“…Recently, we have worked on the determination of enantiomeric composition of various analytes with soluble analogs of Pirkle-type chiral stationary phase (CSP) [47][48][49][50][51][52][53] as chiral selectors using single-stage ESI-MS of solutions containing the analyte of interest and a mixture of pseudo-enantiomeric chiral selectors [54][55][56][57]. For example, the (S)-butyl amide, 8 (see Chart 1), and the (R)-pentyl amide of N-(3,5-dinitrobenzoyl)leucine (pseudoenantiomeric antipode of 8 with a five-carbon chain attached on nitrogen of amide group), form a pseudo-enantiomeric pair "pseudo-enantiomeric" means the two selectors behave as enantiomers even though their mass differs by 14 amu due to the length of the alkyl group which is not involved in the chiral recognition process.…”

“…In order to determine whether chiral recognition would be observed in the reciprocal sense, our group had investigated the enantioselectivity of pseudo-enantiomeric chiral selectors (S)-2 and (R)-3 (Chart 1), using ester or amide derivatives of 3,5-dintrobenzoyl amino acids, such as 8 as analyte by ESI-MS [57]. MS enantioselectivity values (˛M S ) were increased by optimizing the experimental conditions, including desolvation temperature, cone voltage, and additives.…”