The 2-alkyl-2 H-indazole regioisomers of synthetic cannabinoids AB-CHMINACA, AB-FUBINACA, AB-PINACA, and 5F-AB-PINACA are possible manufacturing impurities with cannabimimetic activities

Mitchell Longworth; Samuel D Banister; James B C Mack; Michelle Glass; Mark Connor; Michael Kassiou

doi:10.1007/s11419-016-0316-y

The 2-alkyl-2 H-indazole regioisomers of synthetic cannabinoids AB-CHMINACA, AB-FUBINACA, AB-PINACA, and 5F-AB-PINACA are possible manufacturing impurities with cannabimimetic activities

Forensic Toxicol. 2016:34:286-303. doi: 10.1007/s11419-016-0316-y. Epub 2016 Apr 27.

Authors

Mitchell Longworth^#¹, Samuel D Banister^#^{1

2}, James B C Mack³, Michelle Glass⁴, Mark Connor⁵, Michael Kassiou^{1

6}

Affiliations

¹ School of Chemistry, The University of Sydney, Sydney, NSW 2006 Australia.
² Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA USA.
³ Department of Chemistry, Stanford University, Stanford, CA USA.
⁴ School of Medical Sciences, The University of Auckland, Auckland, New Zealand.
⁵ Department of Biomedical Sciences, Macquarie University, Sydney, Australia.
⁶ Faculty of Health Sciences, The University of Sydney, Sydney, Australia.

^# Contributed equally.

Abstract

Indazole-derived synthetic cannabinoids (SCs) featuring an alkyl substituent at the 1-position and l-valinamide at the 3-carboxamide position (e.g., AB-CHMINACA) have been identified by forensic chemists around the world, and are associated with serious adverse health effects. Regioisomerism is possible for indazole SCs, with the 2-alkyl-2H-indazole regioisomer of AB-CHMINACA recently identified in SC products in Japan. It is unknown whether this regiosiomer represents a manufacturing impurity arising as a synthetic byproduct, or was intentionally synthesized as a cannabimimetic agent. This study reports the synthesis, analytical characterization, and pharmacological evaluation of commonly encountered indazole SCs AB-CHMINACA, AB-FUBINACA, AB-PINACA, 5F-AB-PINACA and their corresponding 2-alkyl-2H-indazole regioisomers. Both regioisomers of each SC were prepared from a common precursor, and the physical properties, ¹H and ¹³C nuclear magnetic resonance spectroscopy, gas chromatography-mass spectrometry, and ultraviolet-visible spectroscopy of all SC compounds are described. Additionally, AB-CHMINACA, AB-FUBINACA, AB-PINACA, and 5F-AB-PINACA were found to act as high potency agonists at CB₁ (EC₅₀ = 2.1-11.6 nM) and CB₂ (EC₅₀ = 5.6-21.1 nM) receptors in fluorometric assays, while the corresponding 2-alkyl-2H-indazole regioisomers demonstrated low potency (micromolar) agonist activities at both receptors. Taken together, these data suggest that 2-alkyl-2H-indazole regioisomers of AB-CHMINACA, AB-FUBINACA, AB-PINACA, and 5F-AB-PINACA are likely to be encountered by forensic chemists and toxicologists as the result of improper purification during the clandestine synthesis of 1-alkyl-1H-indazole regioisomers, and can be distinguished by differences in gas chromatography-mass spectrometry fragmentation pattern.

Keywords: 2H-indazole regioisomer; CHMINACA; FUBINACA; Indazole synthetic cannabinoid; Manufacturing impurity with cannabinoid activity; PINACA.