Enantioseparation of the carboxamide-type synthetic cannabinoids N-(1-amino-3-methyl-1-oxobutan-2-yl)-1-(5-fluoropentyl)-1H-indazole-3-carboxamide and methyl [1-(5-fluoropentyl)-1H-indazole-3-carbonyl]-valinate in illicit herbal products

Abstract Synthetic cannabinoids, recently used as alternatives to Cannabis sativa , are among the most frequently abused drugs. Identified in 2014, the synthetic cannabinoids N -(1-amino-3-methyl-1-oxobutan-2-yl)-1-(5-fluoropentyl)-1 H -indazole-3-carboxamide (5F-AB-PINACA) and methyl [1-(5-fluoropentyl)-1 H -indazole-3-carbonyl]-valinate (5F-AMB) are carboxamides composed of 1-(5-fluoropentyl)-1 H -indazole-3-carboxylic acid and valine amide/methyl ester. Because of their composition, these molecules have pairs of enantiomers derived from the chiral center of their amino acid structures. Previous studies on the identification of 5F-AB-PINACA and 5F-AMB did not consider the existence of enantiomers, and there have been no reports on the enantiopurities of synthetic cannabinoids. We synthesized both enantiomers of these compounds and then separated the enantiomers by liquid chromatography–high-resolution mass spectrometry using a column with a chiral stationary phase consisted with amylose tris (3-chloro-4-methylphenylcarbamate). Under the optimized conditions, the enantiomer resolutions were 2.2 and 2.3 for 5F-AB-PINACA and 5F-AMB, respectively. Analysis of 10 herbal samples containing 5F-AB-PINACA and one herbal sample containing 5F-AMB showed that they all contained the ( S )-enantiomer, but the ( R )-enantiomer was only detected in two samples and at a ratio of less than 20%.