Mephedrone and other Methylmethcathinone (MMC) Identification via Benchtop NMR

Cathinone is a natural alkaloid occurring in the khat plant¹ known for its mild stimulating effects when chewing the leaves which is of cultural importance in East Africa and the Middle East.² Synthetic cathinone derivatives played a big role in the emergence of the new psychoactive substances (NPS) grey market in the 2000s and were sold online mislabeled as “bath salts” or “research chemicals” trying to circumvent potential control mechanisms.³ Cathinones show strong structural similarities to other phenylethylamine based drugs as shown in comparison with amphetamine and methamphetamine in Figure 1. Cathinones share the β-keto amphetamine (cathinone) core structure.

Figure 1. Molecular structures of some phenylethylamine based drugs.

One subgroup of this class are methylmethcathinones. Mephedrone, or 4-methylmethcathinone (4-MMC), appeared earlier on the market than its ortho- and meta-substituted isomers, 2-MMC and 3-MMC. It was mainly traded over the internet as a legal-high alternative for amphetamine (‘speed’) or cocaine. Similar to derivatization strategies for other drugs, when 4-MMC became a controlled substance, its uncontrolled derivatives 2-MMC and 3-MMC were introduced to the grey market. During 2020, a strong increase of cathinone seizures in Europe was reported by the European Monitoring Center for Drugs and Drug Addiction (EMCDDA) and the recently re-emerging 3-MMC made up for nearly ¼ of all seized cathinones.⁴

Before new legislations started regulating new psychoactive substances (NPS) based on general structural motifs, only specific substances were controlled and their derivates were not covered. While, the legal situation became easier with the introduction of these legislations, the executive authorities (custom border laboratories or other forensic analysis sites) are challenged with the detection of the continuously growing list of new designer drugs.

We have previously discussed the capability of benchtop NMR identifying both, similarities and differences in molecular structures even for almost identical substances and the methylmethcathinones are just another example. In Figure 2, the 60 MHz ¹H NMR spectra of the regioisomers 2-MMC, 3-MMC, and 4-MMC are shown.

Figure 2. Stacked 60 MHz 1H NMR spectra of the three methylmethcathinone (MMC) isomers. The residual solvent signal is indicated by an asterisk (*) and the water signal by a hash mark (#).

At first glance the spectra look very similar, which is due to the electronic environment of many hydrogen atoms being effectively the same for the three isomers. However, and this is to emphasize here, despite their similarity (and potentially exact same fragment pattern in mass spectrometry), the isomers show differences especially in the aromatic areas of their NMR spectra. The para-substitution pattern of the aromatic signals 2 and 3 between 8 to 7 ppm clearly identifies mephedrone (4-MMC). 2-MMC and 3-MMC show stronger second order effects in this range and the substitution pattern cannot be as easily extracted. However, the integration ratio of the signals 2 and 3 differentiates the ortho- and meta-substituted methylmethcathinones. For 2-MMC we find an integration ratio of 1:3, while in 3-MMC it reads 2:2.

This highlights the structural information available from NMR spectra and the capabilities of benchtop NMR for flagging new designer drugs. The NMR spectra of potential previously unknown drugs will match partially with their derivative spectra in manual or automated comparison via database searches. Quick and easy sample preparation and short spectral acquisition times of suspicious samples are further advantages. If you have any questions about forensic analysis applications for benchtop NMR, please don't hesitate to contact us.

[1] Report on the risk assessment of mephedrone in the framework of the Council Decision on new psychoactive  substances, EMCDDA, https://www.emcdda.europa.eu/system/files/publications/571/TDAK11001ENC_WEB-OPTIMISED_FILE_280269.pdf  (accessed Sept 16, 2022).

[2] https://en.wikipedia.org/wiki/Cathinone (accessed Sept 16, 2022).

[3] Europol–EMCDDA Joint Report on a new psychoactive substance: 4-methylmethcathinone (mephedrone), https://www.emcdda.europa.eu/system/files/publications/559/2010_Mephedrone_Joint_report_279863.pdf (accessed Sept 16, 2022).

[4] Report on the risk assessment of 2-(methylamino)-1-(3-methylphenyl)propan-1-one (3-methylmethcathinone, 3-MMC) in accordance with Article 5c of Regulation (EC) No 1920/2006 (as amended), EMCDDA,https://www.emcdda.europa.eu/system/files/publications/14507/Report%20on%20the%20risk%20assessdatement%20of%203-MMC.pdf (accessed Sept 16, 2022).