Synthesis and identifications of potential metabolites as biomarkers of the synthetic cannabinoid AKB-48

Synthesis and structure determination of a synthetic cannabinoid CUMYL-THPINACA metabolite with differentiation between the ortho-, meta-, and para-hydroxyl positions of the cumyl moiety

Synthetic cannabinoids, a type of new psychoactive substances, are likely to be rapidly metabolized; thus, the detection of their metabolites, rather than the parent compound, is a common method used to prove drug consumption. Although the analysis of metabolites is generally performed by mass spectrometry, it is limited to structural estimation because of few commercially available standards. In particular, distinguishing between positional isomers is difficult. Synthetic cannabinoids with a cumyl moiety can be hydroxylated at the cumyl moiety during metabolism, but it remains unclear whether the hydroxylation occurs at the ortho, meta, or para position. This study determined the structures of a metabolite formed by mono-hydroxylation at the cumyl moiety of the synthetic cannabinoid CUMYL-THPINACA, used as a model compound. Chemical synthesis was performed to create possible metabolites with one hydroxyl group at the ortho, meta, or para positions of the cumyl moiety. Using the synthesized metabolites and liquid chromatography-quadrupole time-of-flight mass spectrometry, the metabolite detected in the microsomal reaction of CUMYL-THPINACA was identified as a compound mono-hydroxylated at the para position based on retention time and product ion spectra. Moreover, the rapid metabolism of CUMYL-THPINACA was demonstrated with an in vitro half-life of 4.9 min and the identified metabolite could be detected for a relatively long time in vitro. The synthesized metabolite may be utilized as a good reference standard for proof of CUMYL-THPINACA consumption. These findings have potential applications in the synthesis of metabolites of other synthetic cannabinoids bearing a cumyl moiety.

The metabolic profile of the synthetic cannabinoid receptor agonist ADB-HEXINACA using human hepatocytes, LC-QTOF-MS and synthesized reference standards

Synthetic cannabinoid receptor agonists (SCRAs) remain a major public health concern, with their use implicated in intoxications and drug-related deaths worldwide. Increasing our systematic understanding of SCRA metabolism supports clinical and forensic toxicology casework, facilitating the timely identification of analytical targets for toxicological screening procedures and confirmatory analysis. This is particularly important as new SCRAs continue to emerge on the illicit drug market. In this work, the metabolism of ADB-HEXINACA (ADB-HINACA, N-[1-amino-3,3-dimethyl-1-oxobutan-2-yl]-1-hexyl-1H-indazole-3-carboxamide), which has increased in prevalence in the United Kingdom and other jurisdictions, was investigated using in vitro techniques. The (S)-enantiomer of ADB-HEXINACA was incubated with pooled human hepatocytes over 3 hours to identify unique and abundant metabolites using liquid chromatography-quadrupole time-of-flight mass spectrometry. In total, 16 metabolites were identified, resulting from mono-hydroxylation, di-hydroxylation, ketone formation (mono-hydroxylation then dehydrogenation), carboxylic acid formation, terminal amide hydrolysis, dihydrodiol formation, glucuronidation and combinations thereof. The majority of metabolism took place on the hexyl tail, forming ketone and mono-hydroxylated products. The major metabolite was the 5-oxo-hexyl product (M9), while the most significant mono-hydroxylation product was the 4-hydroxy-hexyl product (M8), both of which were confirmed by comparison to in-house synthesized reference standards. The 5-hydroxy-hexyl (M6) and 6-hydroxy-hexyl (M7) metabolites were not chromatographically resolved, and the 5-hydroxy-hexyl product was the second largest mono-hydroxylated metabolite. The structures of the terminal amide hydrolysis products without (M16, third largest metabolite) and with the 5-positioned ketone (M13) were also confirmed by comparison to synthesized reference standards, along with the 4-oxo-hexyl metabolite (M11). The 5-oxo-hexyl and 4-hydroxy-hexyl metabolites are suggested as biomarkers for ADB-HEXINACA consumption.

In vitro metabolic profiling of new synthetic cannabinoids, ADB-FUBIATA, AFUBIATA, CH-FUBIATA, and CH-PIATA

In the recreational drug market, synthetic cannabinoids with a new acetamide linker structure emerged, most likely to circumvent the law. As the knowledge of drug metabolites is vital for proving drug consumption, the phase I metabolism of the newly emerging cannabinoids, ADB-FUBIATA, AFUBIATA, CH-FUBIATA, and CH-PIATA, was investigated. Each drug (10 μmol/L) was incubated with human liver microsomes for 1 h, and the samples, after dilution, were analyzed by liquid chromatography-high-resolution mass spectrometry. All drugs were metabolized via hydroxylation and N-dealkylation, while AFUBIATA and CH-PIATA additionally underwent ketone formation. The metabolites AF7 (hydroxylated at the indole/adjacent methylene) of ADB-FUBIATA, A16 (hydroxylated at the adamantane) of AFUBIATA, CF15 (hydroxylated at the cyclohexane) of CH-FUBIATA, and CP9 (hydroxylated at the pentane) of CH-PIATA were the most abundant metabolites by considering the peak areas on the chromatograms, and are recommended for urinalysis. The structure-metabolism relationship was also discussed, which generally agreed well with previously reported metabolic pathways of other synthetic cannabinoids. However, the preferred hydroxylation site of ADB-FUBIATA, the indole/adjacent methylene, clearly differed from that of ADB-FUBICA, the 3,3-dimethylbutanamide moiety, despite their structures differing only by a methylene group, emphasizing that metabolic predictions of new drugs should not replace in vitro experimental analyses, albeit helpful.

Ozone-Mediated Amine Oxidation and Beyond: A Solvent-Free, Flow-Chemistry Approach

Ozone is a powerful oxidant, most commonly used for oxidation of alkenes to carbonyls. The synthetic utility of other ozone-mediated reactions is hindered by its high reactivity and propensity to overoxidize organic molecules, including most solvents. This challenge can largely be mitigated by adsorbing both substrate and ozone onto silica gel, providing a solvent-free oxidation method. In this manuscript, a flow-based packed bed reactor approach is described that provides exceptional control of reaction temperature and time to achieve improved control and chemoselectivity over this challenging transformation. A powerful method to oxidize primary amines into nitroalkanes is achieved. Examples of pyridine, C-H bond, and arene oxidations are also demonstrated, confirming the system is generalizable to diverse ozone-mediated processes.

Synthetic cannabinoids in e-liquids: A proton and fluorine NMR analysis from a conventional spectrometer to a compact one

The ¹H NMR profiles of 13 samples of e-liquids supplied by French customs were obtained with high-field and low-field NMR. The high-field ¹H NMR spectra allowed the detection of matrix signals, synthetic cannabinoids, and flavouring compounds. Quantitative results were obtained for the five synthetic cannabinoids detected: JWH-210, 5F-MDMB-PICA, 5F-ADB, 5F-AKB48, and ADB-FUBINACA. Conventional GC-MS analysis was used to confirm compound identification. Fluorine-19 NMR was proposed for the quantification of fluorinated synthetic cannabinoids and was successfully implemented on both 400 MHz and 60 MHz NMR spectrometers. This study based on few examples explored the potentiality of low-field NMR for quantitative and quantitative analysis of synthetic cannabinoids in e-liquids.

Systematic evaluation of a panel of 30 synthetic cannabinoid receptor agonists structurally related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA using a combination of binding and different CB1 receptor activation assays: Part I-Synthesis, analytical characterization, and binding affinity for human CB1 receptors

Synthetic cannabinoid receptor agonists (SCRAs) are one of the largest and most structurally diverse classes of new psychoactive substances (NPS). Despite this, pharmacological data are often lacking following the identification of a new SCRA in drug markets. In this first of a three-part series, we describe the synthesis, analytical characterization, and binding affinity of a proactively generated, systematic library of 30 indole, indazole, and 7-azaindole SCRAs related to MMB-4en-PICA, MDMB-4en-PINACA, ADB-4en-PINACA, and MMB-4CN-BUTINACA featuring a 4-pentenyl (4en-P), butyl (B/BUT), or 4-cyanobutyl (4CN-B/BUT) tail and a methyl l-valinate (MMB), methyl l-tert-leucinate (MDMB), methyl l-phenylalaninate (MPP), l-valinamide (AB), l-tert-leucinamide (ADB), l-phenylalaninamide (APP), adamantyl (A), or cumyl head group. Competitive radioligand binding assays demonstrated that the indazole core conferred the highest CB₁ binding affinity (K_i  = 0.17-39 nM), followed by indole- (K_i  = 0.95-160 nM) and then 7-azaindole-derived SCRAs (K_i  = 5.4-271 nM). Variation of the head group had the greatest effect on binding, with tert-leucine amides and methyl esters (K_i  = 0.17-14 nM) generally showing the greatest affinities, followed by valine derivatives (K_i  = 0.72-180 nM), and then phenylalanine derivatives (K_i  = 2.5-271 nM). Adamantyl head groups (K_i  = 8.8-59 nM) were suboptimal for binding, whereas the cumyl analogues consistently conferred high affinity (K_i  = 0.62-36 nM). Finally, both butyl (K_i  = 3.1-163 nM) and 4-cyanobutyl (K_i  = 5.5-44 nM) tail groups were less favorable for CB₁ binding than their corresponding 4-pentenyl counterparts (K_i  = 0.72-25 nM).

Metabolic Profiling of a CB2 Agonist, AM9338, Using LC-MS and Microcoil-NMR: Identification of a Novel Dihydroxy Adamantyl Metabolite

Adamantyl groups are key structural subunit commonly used in many marketed drugs targeting diseases ranging from viral infections to neurological disorders. The metabolic disposition of adamantyl compounds has been mostly studied using LC-MS based approaches. However, metabolite quantities isolated from biological preparations are often insufficient for unambiguous structural characterization by NMR. In this work, we utilized microcoil NMR in conjunction with LC-MS to characterize liver microsomal metabolites of an adamantyl based CB2 agonist AM9338, 1-(3-(1H-1,2,3-triazol-1-yl) propyl)-N-(adamantan-1-yl)-1H-indazole-3-carboxamide, a candidate compound for potential multiple sclerosis treatment. We have identified a total of 9 oxidative metabolites of AM9338 whereas mono- or di-hydroxylation of the adamantyl moiety is the primary metabolic pathway. While it is generally believed that the tertiary adamantyl carbons are the preferred sites of CYP450 oxidation, both the mono- and di-hydroxyl metabolites of AM9338 show that the primary oxidative sites are located on the secondary adamantyl carbons. To our knowledge this di-hydroxylated metabolite is a novel adamantyl metabolite that has not been reported before. Further, the stereochemistry of both mono- and di-hydroxyl adamantyl metabolites has been determined using NOE correlations. Furthermore, docking of AM9338 into the CYP3A4 metabolic enzyme corroborates with our experimental findings, and the modelling results also provide a possible mechanism for the unusual susceptibility of adamantyl secondary carbons to metabolic oxidations. The novel dihydroxylated AM9338 metabolite identified in this study, along with the previously known adamantyl metabolites, gives a more complete picture of the metabolic disposition for adamantyl compounds.