Impurity profiling of methamphetamine synthesised from α-phenylacetoacetonitrile (APAAN)

Changes in methamphetamine impurity profiles induced by tert-butoxycarbonylation

Analysis of impurities in methamphetamine (MA) can be used to characterize MA seizures, investigate the relationship among MA seizures, and provide information on their synthetic routes. Recently, chemically derivatized MA, such as tert-butoxycarbonyl (t-Boc) MA, has been seized and attracted attention because routine forensic analysis methods may fail to correctly identify them. Chemical derivatization is a simple method for protection and deprotection of a compound, and protection of MA using t-Boc can be used to mask the MA. Although t-Boc derivatization might alter the impurity profile of MA, the actual changes in the impurity profile have not been investigated. In this study, changes in the MA impurity profile with tert-butoxycarbonylation were explored. MA and some typical impurities were derivatized using di-tert-butyl dicarbonate and water. Analysis of the impurities in five MA samples by gas chromatography showed that peaks both appeared and disappeared for the deprotected MA compared with the original MA. However, typical impurities important for characterizing MA seizures were conserved after derivatization and deprotection. Most of the new peaks were speculated to be contaminants introduced during derivatization and deprotection. A peak giving a mass spectrum similar to that of t-Boc MA was detected in the chromatograms of t-Boc MA and deprotected MA. Although the origin of this peak was not determined, it might be a marker for the MA involving tert-butoxycarbonylation. These results indicate that tert-butoxycarbonylation can alter the MA impurity profile; therefore, care is needed when interpreting results for derivatized MA.

Impurity profiling of methamphetamine synthesized from methyl α-acetylphenylacetate

The group of P2P precursors including α-phenylacetoacetonitrile (APAAN), α-phenylacetoamide (APAA) and methyl α-acetylphenylacetate (MAPA) has become increasingly popular in Europe and other parts of the world in the last decade. Previous investigations have reported the use of APAAN in the synthesis of amphetamine and methamphetamine and identified a range of characteristic impurities. This research has expanded upon the current literature by investigating the use of MAPA in the synthesis of methamphetamine. In this study methamphetamine was synthesized via three common clandestine methods: the Leuckart synthesis and two reductive amination methods. We report the identification of seven impurities, four of which are methyl ester equivalents of impurities previously reported for the detection of APAAN. These are methyl 2-phenylbut-2-enoate, methyl 2-phenyl-3-hydroxybutanoate, methyl 3-(methylamino)-2-phenylbut-2-enoate and methyl 3-(methylamino)-2-phenylbutanoate. The other impurities identified are ethyl ester compounds formed via transesterification of the methyl ester due to the reaction solvent. This susceptibility for transesterification suggests that identification of the pre-precursor used may not always be straightforward and may be dependent on the reaction conditions employed. Of the impurities reported, methyl 3-(methylamino)-2-phenylbutanoate was deemed to be a potentially reliable impurity for detection of the use of MAPA; however, it is expected that lower levels of characteristic impurities may be detected in methamphetamine synthesized from MAPA than that from APAAN.