LC-MS detection of amino acids and neurotransmitters by using α-active 2,4,5-triphenylpyrylium salt as an efficient derivatizing material

Abstract

Herein, a series of pyrylium salts such as 2,4,6-trimethylpyrylium (P1), 2,6-dimethyl,4-phenylpyrylium (P2), 2,4-diphenylpyrylium (P3), 2,6-diphenylpyrylium (P4), 2,4,5-triphenylpyrylium (P5), 2,4,6-triphenylpyrylium (P6), 2-phenyl, 4,5-diphenylmethylprrylium (P7), 2,3,4,5-tetraphenylpyrylium (P8), 2,3,4,5,6-pentaphenylpyrylium (P9) and 3,4-dimethoxybenzyl,6-phenylpyrylium (P10) were used as highly specific derivatizing agent for mass spectrometric detection of neurochemicals (neurotransmitters and amino acids). Neurotransmitters of dopamine (DA), norepinephrine (NE), histamine (His), γ-amino butyric acid (GABA) and 5-hydroxytyramine (5-HT), and the amino acids of alanine (Ala), serine (Ser), proline (Pro), tryptophan (Trp), threonine (Thr), 4-hydroxy proline (4-Hyp), isoleucine (Ile), leucine (Leu), aspargine (Asn), aspartic acid (Asp), glutamine (Gln), lysine (Lys), glutamic acid (Glu), histidine (H), phenylalanine (Phe), arginine (Arg), valine (Val), tyrosine (Tyr) and cysteine (Cys) were successfully derivatized with the pyrylium salts. The hydrophobic and hydrophilic nature of pyrylium salts were modified by changing the side chain groups. The influence of pyrylium concentration, catalyst concentration, temperature and reaction time were thoroughly optimized. The obtained result suggests that the small molecules like neurotransmitters, amino acids and small peptides have better sensitivity than the peptides and intact proteins. We believe that hydrophobic pyrylium salts will be a potential derivatizing agent for the future mass spectrometric analysis using clinical samples.