Structural Characterization of Emerging Synthetic Drugs

Abstract

Structural Characterization of Emerging Synthetic Drugs J. Tyler Davidson The identification of well-characterized seized drugs is performed thousands of times a day in the United States; however, the expanding use of emerging synthetic drugs is creating a growing problem for both toxicological and seized drug analyses. Two of the most rapidly growing areas of emerging synthetic drugs are synthetic cathinones and fentanyl-related compounds (FRCs). In this work we demonstrate the combination of multi-stage mass spectrometry (MS n), accurate mass measurements with high-resolution mass spectrometry (HRMS), and isotopic labeling for the structural characterization of synthetic cathinones and fentanyl analogs. The deliverables of this research include the identification of conserved fragmentation pathways for synthetic cathinones and fentanyl analogs, proposed mechanisms for the formation of characteristic ions through both protonated tandem mass spectrometry (MS/MS) and electron ionization mass spectrometry (EI-MS), and a discussion about how to apply the broadened understanding of the fragmentation behavior to the identification of novel synthetic cathinones and fentanyl analogs. The first major finding about the fragmentation behavior of synthetic cathinones is that the tropylium ion (m/z 91), or substituted derivative thereof, forms through different oxygencontaining intermediates that do not contain a formal C=O bond but instead contain a phthalanelike core structure. The phthalane-like intermediates were elucidated through gas-phase ion spectroscopy measurements and density functional theory (DFT) calculations. Likewise, the use of stable isotope labeling revealed the unprecedented finding that, during collision-induced dissociation (CID) of α-pyrrolidinophenone synthetic cathinones, the α-carbon is retained almost exclusively in the tropylium ion and the carbonyl carbon is not retained in the tropylium ion. Isotope labeling also identified competitive pathways for the loss of CO and ethylene (C2H4) from a primary intermediate ion, which provides support for the direct loss of CO from the alkyl side chain. A second major finding was the identification of characteristic protonated MS/MS fragmentation pathways and proposed mechanistic origins for both protonated MS/MS and EI-MS fragmentation for α-pyrrolidinophenone and N-alkylated synthetic cathinones. For MS/MS spectra of protonated α-pyrrolidinophenone synthetic cathinones the dominant fragmentation pathways are through 4-center hydrogen rearrangements to produce pyrrolidine ring cleavage, characteristic iminium ions and diagnostic ions at m/z 91 and m/z 105. For EI mass spectra, radical-directed αcleavages result in dominant iminium ions. In contrast to α-pyrrolidinophenone synthetic cathinones, MS/MS of protonated N-alkylated synthetic cathinones provided abundant radical losses from both the N-alkylated and aliphatic side chains, a dominant loss of H2O for 2° amines and the formation of abundant alkylphenones for 3° amines. These findings help advance our cu...

PyFragMS─A Web Tool for the Investigation of the Collision-Induced Fragmentation Pathways

“…One peak with m / z 135 was not annotated. In Figure E, the correct pathway that leads to this fragment formation is shown, as was described by Davidson . This pathway was proven by authors using MS n experiments, DFT calculations, and infrared ion spectroscopy.…”

“…In Figure 3 E, the correct pathway that leads to this fragment formation is shown, as was described by Davidson. 70 This pathway was proven by authors using MS n experiments, DFT calculations, and infrared ion spectroscopy. Unfortunately, currently, our algorithm cannot account for possible intramolecular rearrangement.…”

“…(E) Correct fragmentation pathway and structure for the 135 ion proved using MS n experiments, DFT calculations, and infrared ion spectroscopy. 70 (F) Annotation of fragment ions proposed by MzCloud and MetFrag. The selected m / z = 135.05 was annotated wrong.…”

“…(D 1 ,D 2 ) Computed fragmentation trees for different protonation sites. (E) Correct fragmentation pathway and structure for the 135 ion proved using MS n experiments, DFT calculations, and infrared ion spectroscopy . (F) Annotation of fragment ions proposed by MzCloud and MetFrag.…”