Impurity profiling and synthesis of precursors to the hallucinogenic amphetamine DOB

DOB (4‐bromo‐2,5‐dimethoxyamphetamine) is a newly emerging hallucinogenic amphetamine that sparked serious health warnings in Ireland, following its first seizure back in 2003. Known more commonly as “snowball”, this drug is highly potent and may be used as a substitute to ecstasy (MDMA) and lysergic acid diethylamide (LSD). To date, the work carried out on the impurity profiling of DOB is limited in comparison to amphetamine, methamphetamine and MDMA. In this work, the impurity profile of 4‐bromo‐2,5‐dimethoxyphenyl‐2‐propanone (4‐Br‐2,5‐P2P) is explored. This ketone is a direct precursor to DOB. Its more versatile non‐bromo analogue, 2,5‐ dimethoxyphenyl‐2‐propanone (2,5‐P2P) is also examined, as in addition to DOB, it may be used in the synthesis of a range of several other hallucinogenic amphetamines. A number of different routes to both 2,5‐P2P and 4‐Br‐2,5‐P2P were investigated. For each of these routes, the impurities produced were carefully isolated. Following isolation, the impurities were fully characterised (by 1H‐NMR/13C‐NMR spectroscopy, IR, MS), in order to aid structure elucidation. Compounds not easily resolved by flash column chromatography were analysed by LC‐MS and/or independently synthesised for the purpose of attaining reference standards. Adaptation of the well‐known ‘phenylacetic acid route’ to synthesis of both 2,5‐P2P and 4‐Br‐2,5‐P2P, was found to provide low yields of the expected ketone products. Four impurities were isolated during the preparation of both ketones. The yield of one of these impurities (possessing a dibenzylketone core), was greatly influenced by the amount of acetic anhydride reagent used during the reaction. Having carried out the reaction with several different equivalents of acetic anhydride, it was found that formation of the ‘dibenzylketone’ could not be eliminated. This may increase its likelihood of being detected in the final drug product. The ‘Darzens route’, having very recently emerged as a synthetic route to amphetamine and MDMA precursors, was discovered to be a viable route for manufacture of 2,5‐P2P and 4‐Br‐2,5‐P2P. Despite execution of the reaction being more tedious, the route provides superior yields (≈50–60%) to those achieved using the ‘phenylacetic acid route’ (≈35–38%). Incorporation of a bromine atom (at the aromatic 4‐position) is required at some stage during synthesis of DOB. The bromination of many intermediates/starting materials was therefore also examined in detail. Bromination of the acid starting material 2,5‐dimethoxyphenylacetic acid (2,5‐PAA) was found to be clean and high yielding. This was in stark contrast to the bromination of the benzaldehyde starting material, the ketone precursor 2,5‐P2P and the dibenzylketone‐based impurity. Numerous brominated products were isolated from each of these reactions, many of which were novel compounds, and previously unreported as impurities in the literature. The unpredictable/nondescript nature of these brominations is likely to have a significant impact on the impurity profile of illicitly produced DOB.

Synthesis and evaluation of novel ellipticines as potential anti-cancer agents

Ellipticine is a natural product which possesses multimodal anti-cancer activity. This thesis encompasses the synthesis and biological evaluation of novel ellipticine and isoellipticine derivatives as anti-cancer agents. Expanding on previous work within the group utilising vinylmagnesium bromide, derivatisation of the C5 position of ellipticine was accomplished by reaction of a key ketolactam intermediate with Grignard reagents. Corresponding attempts to introduce diverse substitution at the C11 position were unsuccessful, although one novel C11 derivative was produced using an alkyllithium reagent. A panel of novel ellipticinium salts encompassing a range of substitutions at the N2, C9 and N6 positions were prepared. Extensive derivatisation of the N10 position of isoellipticine was undertaken for the first time. Novel substitution in the form of acid and methyl ester functionalities were introduced at the C7 position of isoellipticine while novel C7 aldehyde and alcohol derivatives were synthesised. A large panel of isoellipticinium salts were prepared with conditions adjusted for the reactivity of the alkyl halide. Novel coupling reactions to increase the yield of isoellipticine were attempted but proved unsuccessful. A panel of 54 novel derivatives was prepared and a multimodal analysis of their anti-cancer activity was conducted. The NCI 60-human tumour cell lines screen was a primary source of information on the in vitro activity of compounds with derivatives found to exert potent anticancer effects, with mean GI50 values as low as 1.01 μM across the full range of cancer types and as low as 16 nM in individual cell lines. A second in vitro screen in collaboration with researchers in the University of Nantes identified derivatives which could potently inhibit growth in a p53 mutant NSCLC cell line. The cell cycle effects of a selected panel of isoellipticines were studied in leukaemia cell lines by researchers in the Department of Biochemistry and Cell Biology, UCC. Emerging from this, the therapeutic potential of one of the derivatives in AML was then assessed in vivo in an AML xenograft mouse model, with tumour weight reduced by a factor of 7 in treated mice relative to control.