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An efficient route for the synthesis of 6 drugs belonging to phenethylamine and amphetamine classes in excellent overall yields and high optical purity has been described. The strategy involves introduction of stereogenic centers by means of two-stereocentered Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of racemic syn-benzyloxy epoxide followed by Pd-catalyzed regioselective cationic hydrogenation of amino alcohols as the key reactions.

Commercial manufacturing of benzphetamine hydrochloride along with its impurity profiling is disclosed. Deoxygenation of pseudoephedrine is reported with ～100% retention by shielding the amine group as its tert-butyl carbamate, which is very straightforward to eliminate at the end. Four unknown process-related impurities are isolated from the samples of final API and characterized on the basis of their NMR and mass spectral analysis. Structures of the isolated impurities are confirmed by independent syntheses and coinjecting with the isolated one.

Methamphetamine HCl was synthesized using three variations of the hydriodic acid/red phosphorus (HI/Pred) synthetic route. A Plackett-Burman experimental design was used to determine how reaction parameters affected the isotopic composition of the product. Isotope ratio mass spectrometry results showed only the source of precursor 13C was significant in determining product δ13C; the manufacturer, reaction temperature, time, scale, and source of HI were not significant. The precursor was also the main determinant of product δ2H, with smaller contributions from the HI source for one method. From precursor to product, large δ2H depletion occurred for most samples. Deuterium nuclear magnetic resonance spectroscopy (2H NMR) was used to investigate the specific site of this. Significant fraction of deuterium was observed only at the benzylic position, the site of hydrogen addition during synthesis. Methamphetamine synthesized from ephedrine was shown to be depleted in this position.

We have established a method for quantitative analysis of the deuterium contents (D/H) at the phenyl, methine, benzyl, N-methyl and methyl groups of l-ephedrine/HCl, d-pseudoephedrine/HCl and methamphetamine/HCl by 2H NMR spectroscopy. Comparison of the 5 position-specific D/H values of l-ephedrine/HCl and d-pseudoephedrine/HCl prepared by three methods (chemical synthesis, semichemical synthesis, and biosynthesis) showed that chemically synthesized ephedrines and semi-synthetic ephedrines have highly specific distributions of deuterium at the methine position and at the benzyl position, compared with the other positions. The classification of several methamphetamine samples seized in Japan in terms of the D/H values at these two positions clearly showed that the methamphetamine samples had been synthesized from ephedrines extracted from Ephedra plants or semisynthetic ephedrines but not from synthetic ephedrine. This isotope ratio analysis method should be useful to trace the origins of seized methamphetamine in Southeast Asia.

This present invention relates to a process for preparing benzylated amines by the reaction of an amine selected from methamphetamine and propylhexedrine with benzyl halide. Numerous improvements are obtained by employing the amine in molar excess with respect to benzyl halide, preferably in a molar ratio of 2 to 1. The excess amine is employed to selectively neutralize by-product acid as the amine salt. The amine salt is then separated from the reaction mixture and basified to reclaim starting amine for recycle to the process.