Neurodegenerative disorders like Parkinson’s and Alzheimer’s disease affect millions of
people around the world. Oxidative stress has been implicated in the pathogenesis of a
number of neurodegenerative disorders, cancer and ischemia. The brain is particularly
vulnerable to oxidative damage because of its high utilisation of oxygen, high levels of
polyunsaturated fatty acids, relatively high levels of redox transition metal ions and low levels
of antioxidants. Oxidative stress occurs due to an imbalance in the pro–oxidant and
antioxidant levels. Reactive oxygen/nitrogen species (ROS/RNS) is a collective term used
for free radicals and related molecules, promoting oxidative stress within cells and ultimately
leading to neurodegeneration. Antioxidants counteract the excess in ROS/RNS, and is
therefore of interest in the treatment and prevention of neurodegenerative disorders.
Monoamine oxidases, especially monoamine oxidase B (MAO–B), also play an important role
in neurodegenerative disorders. MAO–B is the main enzyme responsible for the oxidative
deamination of dopamine in the substantia nigra of the brain. By inhibiting MAO–B,
dopamine is increased in the brain providing symptomatic relief in Parkinson’s disease.
The focus of the current study was to synthesise multifunctional compounds that could be
used in the treatment and/or prevention of neurodegenerative diseases. In this study
flavonoids were selected because of their wide spectrum of biological activities, including
antioxidant activity and its monoamine oxidase inhibition. Flavones and chalcones are both
classified under flavonoids and both structures were included. The amantadine moiety was
included because of its known ability to inhibit calcium flux through the N–methyl–D–aspartate
(NMDA) receptor channel. Six amantadine–flavonoid derivatives were synthesised using
standard laboratory procedures and structures were determined with standard methods such
as NMR, IR and mass spectrometry. The synthesised compounds were tested in a selection
of biological assays, to establish the relative antioxidant properties and MAO inhibitory
activity.
The biological assays employed to test antioxidant properties were the thiobarbituric acid
(TBA) and nitro–blue tetrazolium (NBT) assays. The TBA assay relies on the assessment of
lipid peroxidation, induced via hydroxyl anions (OH), generating a pink colour with the
complex formation between malondialdehyde (MDA) and TBA, which is measured
spectrophotometrically at 532 nm. The principal of the NBT assay is the reduction of NBT to
nitro–blue diformazan (NBD), producing a purple colour in the presence of superoxide anions
(O2
–).
The synthesised compounds were also evaluated for their MAO inhibitory activity toward
recombinant human MAO–A and -B and inhibition values were expressed as IC50 values.
The experimental data obtained in the NBT and TBA assay indicated a weak but a significant
ability to scavenge O2
– and OH. In the NBT assay N–(adamantan–1–yl)–2–{3–hydroxy–4–[(2E)–
3–(3–methoxyphenyl)pro–2–enoyl]phenoxy}acetamide (6) had the best results with a 50.47 ±
1.31 uM/mg protein reduction in NBD formation, indicating that the hydroxyl group
contributed to activity. The synthesised compounds were compared to the toxin (KCN) with
a reduction in NDB formation of 69.88 ± 1.59 uM/mg protein. Results obtained from the TBA
assay indicated that the flavone moiety had better OH scavenging ability than that of the
chalcone moiety with N–(adamantan–1–yl)–2–[(5–hydroxy–4–oxo–2–phenyl–4H–chromen–7–
yl)oxy]acetamide (3) showing the best activity at 0.967 ± 0.063 nmol MDA/mg tissue. The
synthesised compounds were compared to the toxin (H2O2) 1.316 ± 0.028 nmol MDA/mg
tissue. None of the test compounds could be compared to the results obtained with Trolox®.
The IC50 values obtained for inhibition of recombinant human MAO indicated that the
chalcone moiety (N–(adamantan–1–yl)–4–[(1E)–3–oxo–3–phenylpro–1–en–1–yl]benzamide (5))
showed the best inhibition of MAO–B with an IC50 of 0.717 ± 0.009 M and of MAO–A with an
IC50 of 24.987 ± 5.988 M. It was further confirmed that N–(adamantan–1–yl)–4–[(1E)–3–oxo–3–
phenylpro–1–en–1–yl]benzamide (5) binds reversible to MAO–B and that the mode of inhibition
is competitive. Docking studies revealed that N–(adamantan–1–yl)–4–[(1E)–3–oxo–3–phenylpro–
1–en–1–yl]benzamide (5) traverses both cavities of MAO–B with the chalcone moiety
orientated towards the FAD co–factor while the amantadine moiety protrudes into the
entrance cavity. / Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/7339 |
| Date | January 2011 |
| Creators | Fourie, Petrus Michiel |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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