Differentiation of structural isomers in a target drug database by LC/Q‐TOFMS using fragmentation prediction

Abstract

Isomers cannot be differentiated from each other solely based on accurate mass measurement of the compound. A liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOFMS) method was used to systematically fragment a large group of different isomers. Two software programs were used to characterize in silico mass fragmentation of compounds in order to identify characteristic fragments. The software programs employed were ACD/MS Fragmenter (ACD Labs Toronto, Canada), which uses general fragmentation rules to generate fragments based on the structure of a compound, and SmartFormula3D (Bruker Daltonics), which assigns fragments from a mass spectra and calculates the molecular formulae for the ions using accurate mass data. From an in-house toxicology database of 874 drug substances, 48 isomer groups comprising 111 compounds, for which a reference standard was available, were found. The product ion spectra were processed with the two software programs and 1-3 fragments were identified for each compound. In 82% of the cases, the fragment could be identified with both software programs. Only 10 isomer pairs could not be differentiated from each other based on their fragments. These compounds were either diastereomers or position isomers undergoing identical fragmentation. Accurate mass data could be utilized with both software programs for structural elucidation of the fragments. Mean mass accuracy and isotopic pattern match values (SigmaFit; Bruker Daltonics Bremen, Germany) were 0.9 mDa and 24.6 mSigma, respectively. The study introduces a practical approach for preliminary compound identification in a large target database by LC/Q-TOFMS without necessarily possessing reference standards.

Kinetic Control of Protonation in Electrospray Ionization

“…Data processing was performed using Bruker DataAnalysis software, including the chemical formula assignment software, SmartFormula (SF) [15][16][17][18][19] and SmartFormula3D (SF3D) [20,21] …”

Combined drug screening and confirmation by liquid chromatography time-of-flight mass spectrometry with reverse database search

“…To deal with the differentiation of isomers, Ferrer and Thurman were the first to publish a comprehensive presentation of qualifier ion sets, for 101 pesticides, by ISCID LC-TOFMS [18]. The accurate mass data of the qualifier ions enables molecular formula assignment, providing precise information of the fragmentation path, especially if combined with in silico tools [19].…”

Computational mass spectrometry for metabolomics: Identification of metabolites and small molecules

“…The commercial software ACD/MS Fragmenter [35] is such a tool that uses a database of fragmentation rules. Pelander et al used both SmartFormula3D and the ACD Fragmenter to differentiate structural isomers in a comparatively low number of phase I metabolites of quetiapine from LC/TOF MS spectra [36], and recently generalized the survey to 111 compounds in 48 isomer groups [37].…”