Molecular approaches to the treatment of motor neuron degeneration
thesisposted on 17.02.2017, 02:22 by Wood, Laura Katherine
This thesis describes methods towards the synthesis and evaluation of potential small molecule agents for the treatment of motor neuron degeneration. Several factors are known to contribute to the mechanisms of neurodegeneration, including cellular degradation caused by the production of radical oxygen species and dysfunction of glutamate transporters and receptors leading to the disruption of Ca2+ homeostasis in neurons. The work undertaken in this thesis attempted to target these factors by incorporating antioxidant and Ca2+-chelating function within the same structure, thus simultaneously combating known pathways towards apoptosis. Chapter One provides a background to the pathogenesis of neurodegenerative disease and specifically amyotrophic lateral sclerosis (ALS). This chapter gives an overview of the many pathways, both genetically inheritable and sporadic, that may lead to the premature activation of apoptotic pathways in neurons, as well as current and proposed approaches towards interrupting these pathways. Chapter Two describes the synthesis of compounds based on the structure of 1,2-bis(o-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid (BAPTA), an effective Ca2+ chelator. As studies have indicated that BAPTA acts as an effective treatment against neurodegeneration but has difficulty crossing the blood brain barrier, modification of BAPTA by the introduction of hydrophilic groups was pursued in this chapter. A number of tetraethyl ester derivatives of BAPTA were synthesised, including bis phenol acid 20 and tetraethyl ester 19, which underwent reaction with 2-(2-chloroethoxy)ethanol to produce the polyethylene glycol derivative 21 and glycosylation to give the protected glucose derivative 23. The target compounds were evaluated for antioxidant potency using a linoleic acid protocol, with results indicating that a number of hydrophilic BAPTA derivatives had moderate to high antioxidant efficiency, particularly phenolic analogues 19 and 20, which exhibited efficiencies comparable to vitamin E. A number of methods towards the formation and functionalisation of chroman cores are investigated in Chapter Three. For the purposes of this project, installation of functionalised chains was required at chroman positions C2 and C8, in order to incorporate Ca2+-chelating arms similar to BAPTA. From mono-protected tri- and dimethylhydroquinone (34 and 39, respectively), reaction with paraformaldehyde and selected alkenes formed C2-functionalised chromans in one step, however it was discovered that a slight increase in the overall yield of 2,5,7-trimethyl chromans was achieved when two-step syntheses via a butoxymethyl intermediate was performed. In an effort to further increase the yields of functionalised 2,5,7-trimethyl chromans, synthesis using mono-acetylated bromo dimethylhydroquinone 61 produced C8 bromo chromans 65 and 66 in high yield, which could be successfully debrominated under reductive conditions to give C8-unsubstituted chromans. Phthalimide 72 was formed from the derivatisation of bromo chroman 66, as means of installing a nitrogen on the C2 chain in a effort towards the synthesis of target compound A. As part of an alternative pathway, several failed attempts were made to form phthalamidyl-functionalised C2 chains via etherification with chromans, thus instead installation of the desired functionality was achieved by reacting acetamide alkene 89 with bromo intermediate 61 to form chroman 90, which contained the desired backbone for future formation of target B (91). Synthetic pathways towards an alternative dual action-target 112 are detailed in Chapter Four. Two different synthetic routes were pursued, the first of which involved chroman core formation by reaction of 2,6-dimethylhydroquinone with methyl vinyl ketone and trimethyl orthoformate, followed by a series of transformations of the C2 chain to give the benzyl protected alcohol 101. Further C2 chain derivatisation and C8 functionalisation yielded the protected target 107 with a total yield of 4% after eleven steps. Alternatively, as a more efficient approach towards the final target, a similar sequence of functionalisation reactions were undertaken with previously synthesised acetate protected alcohol 41, yielding the deprotected target compound 112, which exhibited antioxidant efficiency higher than vitamin E and significantly higher than BAPTA.