Unusual Mass Spectrometric Dissociation Pathway of Protonated Isoquinoline-3-Carboxamides Due to Multiple Reversible Water Adduct Formation in the Gas Phase

• Published in: Journal of the American Society for Mass Spectrometry Vol. 20; no. 11; pp. 2034 - 2048
• Main Authors: Beuck, Simon, Schwabe, Tobias, Grimme, Stefan, Schlörer, Nils, Kamber, Matthias, Schänzer, Wilhelm, Thevis, Mario
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.11.2009; Springer-Verlag; Elsevier; Springer Nature B.V
• Subjects: Adducts; Analytical Chemistry; Bioinformatics; Biotechnology; Carbon monoxide; Carbonyls; Chemical synthesis; Chemistry; Chemistry and Materials Science; Chromatography, Liquid - methods; Disorders; Doping in Sports - prevention & control; Drugs; Exact sciences and technology; Forensic engineering; Fragmentation; Gases - chemistry; Glycine; Humans; Ions; Isoquinolines - analysis; Isoquinolines - chemistry; Mass spectrometry; Mass Spectrometry - methods; Mathematical models; Metabolites; Molecular Structure; Organic Chemistry; Pharmaceutical Preparations - chemistry; Phase Transition; Propylene; Proteomics; Protons; Reactivity and mechanisms; Spectrometry, Mass, Electrospray Ionization - methods; Substance Abuse Detection - methods; Tandem Mass Spectrometry - methods; Water - chemistry; Nuclear Magnetic Resonance; Sport Drug Testing; Prolyl Hydroxylase Domain; Dissociation Pathway; QTrap Mass Spectrometer; Tandem mass spectrometry; Collisional activation; Isoquinoline derivatives; Protonated form; Theoretical study; Density functional method; Carboxamide; Fragmentation pattern; Gas phase; Mass spectrometry; Electrospray
• ISSN: 1044-0305; 1879-1123; 1879-1123
• DOI: 10.1016/j.jasms.2009.07.016

The study of the collision-induced dissociation behavior of various substituted isoquinoline-3-carboxamides, which are amongst a group of drug candidates for the treatment of anemic disorders (e.g., FG-2216), allowed for the formulation of the general mechanisms underlying the unusual fragmentation behavior of this class of compounds. Characterization was achieved with high-resolution/high accuracy LTQ-Orbitrap tandem mass spectrometry of the protonated precursor ions. Presented data were substantiated by the synthesis and analysis of proposed gas-phase intermediate structures and stable isotope labeled analogues, as well as by density functional theory calculations. Exemplary, CID of protonated N-[(1-chloro-4-hydroxy-7-isopropoxy-isoquinolin-3-yl)carbonyl]glycine gives rise to the isoquinoline-3-carboxy-methyleneamide product ion which nominally eliminates a fragment of 11 u. This was attributed to the loss of methyleneamine (−29 u) and a concomitant spontaneous and reversible water addition (+18 u) to the resulting acylium ion to yield the protonated isoquinoline-3-carboxylic acid. The same water addition pattern is observed after loss of propylene (−42 u). A further nominal loss of 10 u is explained by the elimination of carbon monoxide (−28 u) followed by another water adduct formation (+18 u) to yield the protonated 1-chloro-3,4,7-trihydroxy-isoquinoline. The source of the multiple gas-phase water addition remained unclear. This atypical fragmentation pattern proved to be highly characteristic for all studied and differentially substituted isoquinoline-3-carboxamides, and offers powerful analytical tools for the establishment of a LC/MS(/MS) based screening procedure for model HIF-stabilizers and their potential metabolites in clinical, forensic and sports drug testing. The loss of 11 u in ESI-MS/MS spectra of isoquinolines was elucidated. The release of methyleneamine accompanied by an ion-molecule reaction with water was proven.