Discrimination and identification of regioisomeric β-keto analogues of 3,4-methylenedioxyamphetamines by gas chromatography-mass spectrometry

Prediction of designer drugs: Synthesis and spectroscopic analysis of synthetic cathinone analogs that may appear on the Swedish drug market

The use of hyphenated analytical techniques in forensic drug screening enables simultaneous identification of a wide range of different compounds. However, the appearance of drug seizures containing new substances, mainly new psychoactive substances (NPS), is steadily increasing. These new and other already known substances often possess structural similarities and consequently they exhibit spectral data with slight differences. This situation has made the criteria that ensure indubitable identification of compounds increasingly important. In this work, 6 new synthetic cathinones that have not yet appeared in any Swedish drug seizures were synthesized. Their chemical structures were similar to those of already known cathinone analogs of which 42 were also included in the study. Hence, a total of 48 synthetic cathinones making up sets of homologous and regioisomeric compounds were used to challenge the capabilities of various analytical techniques commonly applied in forensic drug screening, ie, gas chromatography-mass spectrometry (GC-MS), gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR), nuclear magnetic resonance (NMR), and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Special attention was paid to the capabilities of GC-MS and GC-FTIR to distinguish between the synthetic cathinones and the results showed that neither GC-MS nor GC-FTIR alone can successfully differentiate between all synthetic cathinones. However, the 2 techniques proved to be complementary and their combined use is therefore beneficial. For example, the structural homologs were better differentiated by GC-MS, while GC-FTIR performed better for the regioisomers. Further, new spectroscopic data of the synthesized cathinone analogs is hereby presented for the forensic community. The synthetic work also showed that cathinone reference compounds can be produced in few reaction steps.

Molecular recognition of pseudodistamine isomeric precursors trans-3(4)-aminopiperidin-4(3)-ols by EI mass spectrometry

Synthesis of drugs, biologically active compounds or their derivatives always requires precise and reliable method of their identification, including differentiation of the possible isomers. Pseudodistamines and their precursors became a matter of elevated attention due to their different enzymatic inhibition. This paper deals with one of the groups of the pseudodistamine precursors - trans-3(4)-aminopiperidin-4(3)-ols. Their synthesis brings to a mixture of 2 regioisomers, resulting in the necessity of their reliable recognition. NMR spectroscopy commonly used by organic chemists requires advance knowledge and experience to analyse the spectra of these regioisomers. Therefore, we herein proposed a simpler way to recognize trans-3(4)-aminopiperidin-4(3)-ols using mass spectrometry with electron ionization. Fragmentation of 4 pairs of aminopiperidinol regioisomers with variation of amine moiety was studied. The obtained results allowed defining a group of 3 ions ([M-18]^+., [M-19]⁺, [M-43]⁺) related only to the structure of trans-4-aminopiperidin-3-ols and 1 ion (m/z 100) related to the structure of trans-3-aminopiperidin-4-ols. Besides, interrogation of intensity of ions common for spectra of both regioisomers allows making differentiation as well.

Development of a mass spectrometric hydroxyl-position determination method for the hydroxyindole metabolites of JWH-018 by GC-MS/MS

One of the many issues of designer drugs of abuse like synthetic cannabinoids (SCs) such as JWH-018 is that details on their metabolism has yet to be fully elucidated and that multiple metabolites exist. The presence of isomeric compounds poses further challenges in their identification. Our group has previously shown the effectiveness of gas chromatography-electron ionization-tandem mass spectrometry (GC-EI-MS/MS) in the mass spectrometric differentiation of the positional isomers of the naphthoylindole-type SC JWH-081, and speculated that the same approach could be used for the metabolite isomers. Using JWH-018 as a model SC, the aim of this study was to differentiate the positional isomers of its hydroxyindole metabolites by GC-MS/MS. Standard compounds of JWH-018 and its hydroxyindole metabolite positional isomers were first analyzed by GC-EI-MS in full scan mode, which was only able to differentiate the 4-hydroxyindole isomer. Further GC-MS/MS analysis was performed by selecting m/z 302 as the precursor ion. All four isomers produced characteristic product ions that enabled the differentiation between them. Using these ions, MRM analysis was performed on the urine of JWH-018 administered mice and determined the hydroxyl positions to be at the 6-position on the indole ring. GC-EI-MS/MS allowed for the regioisomeric differentiation of the hydroxyindole metabolite isomers of JWH-018. Furthermore, analysis of the fragmentation patterns suggests that the present method has high potential to be extended to hydroxyindole metabolites of other naphthoylindole type SCs in identifying the position of the hydroxyl group on the indole ring. Copyright © 2016 John Wiley & Sons, Ltd.

Differentiation of regioisomeric chloroamphetamine analogs using gas chromatography-chemical ionization-tandem mass spectrometry

In recent years, a large number of clandestinely synthesized new psychoactive substances with high structural variety have been detected in forensic samples. Analytical differentiation of regioisomers is a significant issue in forensic drug analysis, because, in most cases, legal controls are placed on only one or two of the conceivable isomers. In this study, gas chromatography-tandem mass spectrometry (GC-MS-MS) was used to differentiate the regioisomers of chloroamphetamine analogs (chloroamphetamines and chloromethamphetamines) synthesized in the authors' laboratories. Free bases, trifluoroacetyl derivatives, and trimethylsilyl derivatives were subjected to GC-MS-MS using DB-1ms, DB-5ms, and DB-17ms capillary columns, respectively. The regioisomers of chloroamphetamine analogs in all forms were well separated on the DB-5ms column. The electron ionization mass spectra of the chloroamphetamine analogs gave very little structural information for differentiation among these analogs, even after trifluoroacetyl and trimethylsilyl derivatization of the analytes. Characteristic product ions of the 2-positional isomers were observed by electron ionization-MS-MS. In contrast, chemical ionization-MS-MS of the free bases provided more structural information about chloride position on the aromatic ring when [M+H-HCl]+ was selected as a precursor ion. The results suggest that a combination of chromatographic analysis and MS-MS supports differentiation for regioisomers of chloroamphetamine analogs.

Positional isomer differentiation of synthetic cannabinoid JWH-081 by GC-MS/MS

Like many new designer drugs of abuse, synthetic cannabinoids (SC) have structural or positional isomers which may or may not all be regulated under law. Differences in acute toxicity may exist between isomers which impose further burden in the fields of forensic toxicology, medicine and legislation. Isomer differentiation therefore becomes crucial from these standpoints as new designer drugs continuously emerge with just minor positional modifications to their preexisting analogs. The aim of this study was to differentiate the positional isomers of JWH-081. Purchased standard compounds of JWH-081 and its positional isomers were analyzed by gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) first in scan mode to investigate those isomers who could be differentiated by EI scan spectra. Isomers with identical or near-identical EI spectra were further subjected to GC-tandem mass spectrometry (MS/MS) analysis with appropriate precursor ions. EI scan was able to distinguish 3 of the 7 isomers: 2-methoxy, 7-methoxy and 8-methoxy. The remaining isomers exhibited near-identical spectra; hence, MS/MS was performed by selecting m/z 185 and 157 as precursor ions. 3-Methoxy and 5-methoxy isomers produced characteristic product ions that enabled the differentiation between them. Product ion spectrum of 6-methoxy isomer resembled that of JWH-081; however, the relative ion intensities were clearly different from one another. The combination of EI scan and MS/MS allowed for the regioisomeric differentiation of the targeted compounds in this study.

The analysis of amphetamine-like cathinone derivatives using positive electrospray ionization with in-source collision-induced dissociation

RATIONALE

Amphetamine-like cathinone derivatives have become popular as recreational drugs over the past several years but their identification for forensic purposes is made difficult as they undergo extensive fragmentation under commonly used electron ionization (EI) conditions to afford ambiguous mass spectra. To overcome this, the feasibility of using positive electrospray ionization (ESI) with in-source collision-induced dissociation (CID) to produce distinguishable product ion mass spectra was examined.

METHODS

A set of six homologous cathinone derivatives was analyzed using an LTQ/Orbitrap™ high-resolution mass spectrometer to establish if there are any commonalities or uniqueness in their mass spectra. These compounds and a number of other cathinone derivatives were also analyzed on a single quadrupole mass spectrometer to establish the feasibility of using in-source CID for their identification in forensic drug samples.

RESULTS

The ESI product ion mass spectra of the [M + H](+) ions of six model compounds were found to be readily interpretable and product ion formation pathways are presented. The use of such mass spectral data in the analysis of forensic drug samples facilitated the discrimination of closely related cathinone derivatives that were difficult to distinguish using conventional gas chromatography/electron ionization mass spectrometry. A product ion mass spectral library of 22 commonly encountered cathinone derivatives was also developed.

CONCLUSIONS

It has been shown that the product ion ESI mass spectra of cathinone derivatives are readily interpretable and are useful for the identification of this drug group in forensic samples.

Fragmentation of oxime and silyl oxime ether odd-electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

The McLafferty rearrangement is an extensively studied fragmentation reaction for the odd-electron positive ions from a diverse range of functional groups and molecules. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by GC-TOF MS and density functional theory calculations. These compounds consisted of three main groups: carbonyls, oximes and silyl oxime ethers. In all electron ionization mass spectra, the fragment ions that could be attributed to the occurrence of a McLafferty rearrangement were observed. For t-butyldimethylsilyl oxime ethers with oxygen in a β-position, the McLafferty rearrangement was accompanied by loss of the t-butyl radical. The various mass spectra showed that the McLafferty rearrangement is relatively enhanced compared with other primary fragmentation reactions by the following factors: oxime versus carbonyl, oxygen versus methylene at the β-position and ketone versus aldehyde. Calculations predict that the stepwise mechanism is favored over the concerted mechanism for all but one compound. For carbonyl compounds, C-C bond breaking was the rate-determining step. However, for both the oximes and t-butyldimethylsilyl oxime ethers with oxygen at the β-position, the hydrogen transfer step was rate limiting, whereas with a CH(2) group at the β-position, the C-C bond breaking was again rate determining. n-Propoxy-acetaldehyde, bearing an oxygen atom at the β-position, is the only case that was predicted to proceed through a concerted mechanism. The synthesized oximes exist as both the (E)- and (Z)-isomers, and these were separable by GC. In the mass spectra of the two isomers, fragment ions that were generated by the McLafferty rearrangement were observed. Finally, fragment ions corresponding to the McLafferty reverse charge rearrangement were observed for all compounds at varying relative ion intensities compared with the conventional McLafferty rearrangement.

Identification of ten new designer drugs by GC-MS, UPLC-QTOF-MS, and NMR as part of a police investigation of a Danish internet company

The ability of forensic laboratories to detect and identify unknown compounds is highly important since new, non-controlled designer drugs are appearing on the market with increasing frequency. In this study, the combined use of gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography-quadrupole time of flight-mass spectrometry (UPLC-QTOF-MS) was used for screening of new unknowns. In one large seizure from a Danish Internet company, ten different drugs were identified. Several of the compounds were seized for the first time in Denmark. The GC-MS and UPLC-QTOF-MS analyses were supplemented by nuclear magnetic resonance (NMR) spectra for the structural elucidation of p-fluoroamphetamine, mephedrone (4-methylmethcathinone), flephedrone (4-fluoromethcathinone), PPP (α-pyrrolidinopropiophenone), MDPV (3,4-methylenedioxypyrovalerone), Bk-MBDB (2-methylamino-1-(3,4-methylenedioxyphenyl)butan-1-one), pFBT (3-(pfluorobenzoyl)-tropane), and JWH-073 (1-butyl-3-(1-naphthoyl)indol), whereas methylone (3,4-methylenedioxymethcathinone) and N-ethylcathinone matched electron impact-mass spectrometry (EI-MS) library spectra and therefore the screenings were considered sufficient. EI-MS spectra and the proposed main fragmentation patterns are presented as well as QTOF-MS exact masses and fragments and NMR chemical shifts. For the β-ketophenylethylamines (mephedrone, flephedrone, PPP, MDPV, Bk-MBDB, methylone, and N-ethylcathinone) some general fragmentation patterns observed in the EI-MS and QTOF-MS spectra are further discussed and compared to other β-ketophenylethylamines.

Fragmentation Pathways of Trifluoroacetyl Derivatives of Methamphetamine, Amphetamine, and Methylenedioxyphenylalkylamine Designer Drugs by Gas Chromatography/Mass Spectrometry

Methamphetamine (MA), amphetamine (AM), and the methylenedioxyphenylalkylamine designer drugs, such as 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyethylamphetamine (MDEA), N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine (MBDB), 3,4-methylenedioxyamphetamine (MDA), and 3,4-(methylenedioxyphenyl)-2-butanamine (BDB), are widely abused as psychedelics. In this paper, these compounds were derivatized with trifluoroacetic (TFA) anhydride and analyzed by gas chromatography/mass spectrometry using electron ionization in positive mode. Gas chromatographic separation for TFA derivatives of all compounds was successfully resolved using an Equity-5 fused silica capillary column with a poly (5% diphenyl-95% dimethylsiloxane) stationary phase. Base peaks or prominent peaks of MA, AM, MDMA, MDEA, MBDB, MDA, and BDB appeared at m/z 154, 140, 154, 168, 168, 135, and 135, respectively. These occurred due to α-cleavage from the amide nitrogen, splitting into the TFA imine species and benzyl or methylenedioxybenzyl cations. Further prominent fragment ions at m/z 118 for MA and AM, m/z 162 for MDMA, MDEA, and MDA, and m/z 176 for MBDB and BDB were produced by cleavage of the phenylpropane or methylenedioxypropane hydrocarbon radical cation via a hydrogen rearrangement. These fragmentation pathways for the TFA derivatives of all the compounds are summarized and illustrated in this paper.

Bioanalysis of new designer drugs

Since the late 1990s the illicit drug market has undergone considerable change: along with the traditional drugs of abuse that still dominate, more than 100 psychotropic substances designed to bypass controlled substances legislation have appeared and led to intoxications and fatalities. Starting from the huge class of phenylalkylamines, containing many subgroups, the spectrum of structures has grown from tryptamines, piperazines, phenylcyclohexyl derivates and pyrrolidinophenones to synthetic cannabinoids and the first synthetic cocaine. Due to the small prevalence and high number of unknown substances, the detection of new designer drugs is a challenge for clinical and forensic toxicologists. Standard screening procedures might fail because a recently discovered or yet unknown substance has not been incorporated in the library used. Nevertheless, many metabolism studies, case reports, screening methods and substance-profiling papers concentrating on single compounds have been published. This review provides an overview of the developed bioanalytical and analytical methods, the matrices used, sample-preparation procedures, concentration of analytes in case of intoxication and also gives a résumé of immunoassay experiences. Additionally, six screening methods for biological matrices with a larger spectrum of analytes are described in more detail.

Analysis of NRG 'legal highs' in the UK: identification and formation of novel cathinones

A large number of cathinone derivatives have shown a wide range of bioactive properties, attracting great interest from communities associated with pharmaceutical research. Some of these derivatives have gained popularity as so-called recreational 'legal highs' due to their availability on the Internet and high street shops. A previous study described the qualitative analysis of 24 'legal high' Energy-1 (NRG-1) and NRG-2 products obtained from 18 websites following the ban on mephedrone and derivatives in April 2010. The majority of these products contained a mixture of cathinones just carrying a new label. Here, three additional cathinone products have been detected; two from an NRG-1 sample and one from an NRG-3 sample. This report describes their identification. NRG-1 sample 1 consisted of a mixture of 4 cathinones namely 4-fluoromethcathinone (1), 1-(3,4-methylenedioxyphenyl)-2-(methylamino)pentan-1-one (pentylone, 2), 3,4-methylenedioxy-α-pyrrolidinobutyrophenone (MDPBP, 3) and 3,4-methylenedioxypyrovalerone (MDPV, 4). The sample labelled as NRG-3 (mislabelled with the chemical structure of mephedrone) consisted of a mixture of 4-methyl-α-pyrrolidinopropiophenone (MPPP, 5) and (2), whereas the remaining NRG-1 sample 2 (also mislabelled with the chemical structure of mephedrone) consisted of a mixture of (2) and (3). Qualitative analyses were carried out by GC-(EI/CI)-MS, NMR spectroscopy and confirmation by preparation of standards. The preparation of brominated precursors carrying the 3,4-methylenedioxyphenyl nucleus revealed extensive α,α-dibromination: the mass spectral and NMR data of these intermediates are also presented and discussed.

Determination of the metabolites of the new designer drugs bk-MBDB and bk-MDEA in human urine

This is the first report on identifying the specific metabolites of the new designer drugs 2-methylamino-1-(3,4-methylenedioxyphenyl)butan-1-one (bk-MBDB) and 2-ethylamino-1-(3,4-methylenedioxyphenyl)propan-1-one (bk-MDEA) in human urine using synthesized standards. Based on GC/MS and LC/MS, we identified N-dealkylation, demethylenation followed by O-methylation, and beta-ketone reduction as their major metabolic pathways. The quantitative analyses by LC/MS revealed that both demethylenation followed by O-methylation and beta-ketone reduction were superior to N-dealkylation and that both bk-MBDB and bk-MDEA were mainly metabolized into their corresponding 4-hydroxy-3-methoxy metabolites (4-OH-3MeO metabolites). After hydrolysis, the concentrations of 4-OH-3MeO metabolites and 3-hydroxy-4-methoxy metabolites of both bk-MBDB and bk-MDEA dramatically increased, suggesting that the metabolites mainly exist as their conjugates.