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Preparation and Characterization of
Manganese (II) Complexes with Potential
Therapeutic Application against α-Synuclein
Aggregation
Kate Byrne
BSc Medicinal Chemistry & Pharmaceutical Science
Year 3 Project
Overview
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Aim of the Project
Parkinson’s Disease and Etiology
α-Synuclein and Lewy Bodies
Project Rationale and Objectives
Synthesis of the compounds
Characterisation of the compounds
Conclusion
Aim
The aim of this project was to synthesize, purify and
characterise three manganese(II) complexes as part of a
structure-activity relationship (SAR) study of a potential
therapeutic system for Parkinson’s disease
Parkinson’s Disease
Parkinson’s disease, (PD) is a progressive neurological
disease which is a result of the loss of dopamine
producing brain cells
Parkinson’s disease is named after Dr. James Parkinson
who first reported symptoms of the disease in 1817 when
it was referred to as “Paralysis Agitans”
Etiology Idiopathic
Figure 1: Dr. James Parkinson
Statistics
• Parkinson’s disease affects 6.3 million people worldwide.
• Over 9,000 of those affected by the disease are Irish.
• The disease typically develops at the age of 65 however
people can develop “early-onset” parkinson’s before
reaching 50 years.
• Current life expectancy: 81 years
• Projected Life expectancy 2030: 90+ years
α-Synuclein
α-Synuclein is a protein that is abundant in the human brain.
In the early stages of Parkinson’s disease misfolded α-synuclein
proteins are converted to pathological oligomers and higher
order aggregates that form fibrils leading to the formation of
Lewy Bodies.
Figure 2: α-Synuclein aggregation stages
Emil Paleek, et al., Changes in interfacial properties of α-synuclein preceding its aggregation, Analyst, 2008, 133,
76.
Lewy bodies and Parkinson’s
Disease
Lewy bodies are abnormal α-Synuclein protein aggregates
that develop in nerve cells in regions of the brain that are
involved in motor control.
The presence of the Lewy Body protein aggregates in the
brain is a pathological hallmark of Parkinson’s Disease.1
Inhibiting α-Synuclein aggregation offers a therapeutic
target for Parkinson’s Disease and evidence in the literature
suggests a role for inorganic medicinal chemistry2
1. He-Jin Lee, et al., Extracellular α-synuclein a novel and crucial factor in Lewy body diseases, Nature Reviews
Neurology, 2014, 10, 92-98.
2. D.J. Haynes, S. Lim, P.S. Donnelly, Metal complexes designed to bind to amyloid-β for diagnosis and treatment of
Alzheimer’s disease, Chem. Soc. Rev., 2014, 43, 6701-6715.
Lead Compound
The complex salt, MD1 has been shown to be an excellent lead
compound for the prevention of α-Synuclein aggregation.
MD1:
[Mn2(oda)(phen)4(H2O)2][Mn2(oda)(phen)4(oda)2]4H2O
Where; odaH2 = octanedioic acid; phen = 1,10-phenanthroline
Figure 4: Structures of MD1 and Octanedioic Acid
• Comprised of bi-nuclear Cationic and Anionic components
(Complex salt).1
• Bridging and terminal octanedioate ligands, deprotonated
octanedioic acid
• Highly water soluble.
• Exhibits antioxidant capability.2
• Reduces α-Synuclein aggregation in fungal (saccharomyces
cerevisiae) and mammalian (HEK293) cellular models.2
1. M. McCann, M. Devereux, et al. Synthesis and structure of the Mn2 (II,II) complex salt [Mn2(oda)(phen)4(H2O)2] [Mn2(oda)2(phen)4]
(odaH2 = octanedioic acid): a catalyst for H2O2 disproportionation., J. Chem. Soc., Chem. Commun., 1994, 2643.
2. T. Ribeiro, M. McCann, M. Devereux, M. Pereira, et al., Evaluation of antioxidant activity of a Mn 2+complex salt and its potential
therapeutic use against alpha—synuclein aggregation. Manuscript in preparation. (Target Journal: Nature Communications)
Research question
What are the structural aspects of
MD1 that are important for its
α-Synuclein aggregation inhibitory
properties?
Objective of the StructureActivity Relationship Study
To investigate analogues of MD1 to determine how
variations in structure influence the α-Synuclein
aggregation inhibitory potential of this class of
manganese(II) complex.
Note: The analogues were varied in terms of the number
of Manganese centres in the complex as well as the charge
on the complex
Key Objectives
To synthesise and characterise three known
analogues of MD1 with variations in
structure achieved by replacing the
octanedioate ligands with aliphatic
dicarboxylic acid ligands of varying chain
length
Octanedioic acid (odaH2)
Hexanedioic acid (hxdaH2)
[Mn(hxda)(phen)2(H2O)].7H2O 1
[Mn(pda)(phen)]2
[Mn2(bda)2(phen)2(H2O)].2H2O3
Pentanedioic acid (pdaH2)
Butanedioic acid (bdaH2)
1. M. McCann, M. Devereux, et al., Manganese(II) complexes of hexanedioic and heptanedioic acids: X-ray crystal structure of
[Mn(hxda)(phen)2(H2O)].7H2O and [Mn(phen)2(H2O)][Mn(hpda)(phen)2(H2O)](hpda) .12.5H2O, Polyhedron, 1997, 16, 2741.
2. Martin Curran, PhD Thesis, DIT/NUIM 1996.
3. M. McCann, M. Devereux, et al., Synthesis, X-ray crystal structure and catalytic activities of manganese(II) butanedioic acid
complexes [Mn(bda)(phen)2(H2O)4].2H2O and {[Mn(bda)(bipy2(H2O)2].H2O }n, Polyhedron, 1997, 16, 2547.
Structure of the Analogue
Complexes
[Mn(hxda)(phen)2(H2O)].7H2O :
Mononuclear (1 manganese centre), 2
phens per manganese, neutral charge
[Mn(pda)(phen)]: Polymeric, 1
phen per manganese, neutral
charge.
[Mn2(bda)2(phen)2(H2O)].2H2O:
Binuclear (2 manganese centres), 1 phen per
manganese, neutral charge
Synthetic Scheme Stage One:
Generation of the manganese(II) dicarboxylate
precursors
Where; R = -(CH2)4 - or -(CH2)3 -or -(CH2)2 -
Synthetic Scheme Stage Two:
Reaction of the precursor complexes with 1,10phenanthroline to produce the analogues of MD1
Reflux
{Mn(OOC-(CH2)n-COO)}x + 4 phen →
EtOH
[Mn(hxda)(phen)2(H2O)].7H2O (where n = 4)
[Mn(pda)(phen)] (where n = 3)
[Mn2(bda)2(phen)2(H2O)].2H2O (where n = 2)
Characterisation
The three precursor complexes and the three analogue
complexes were characterised using the following
techniques:
• Infra-Red (IR) Spectroscopy
• Magnetic Susceptibility Analysis
• Inductively-Coupled Mass Spectrometry (ICP-MS)
Infrared Spectroscopy
An IR spectrum was recorded of:
• The Ligand
• The Precursor Complex
• The Final Complex
Each of the spectra was then overlayed
Hexanedioic Acid
[Mn(hxda)].H2O
[Mn(hxda)(phen)2(H2O)].7H2O
Hexanedioic Acid Spectra
Overlay
Infrared Spectroscopy
Precursor Complex and Analogue Complex Similarities
Characteristic Carbonyl Peak
• Asymmetric Stretch 1590-1547cm-1
• Symmetric Stretch 1400-1420cm-1
Determination of [Mn] Using
ICP
ICP Standards
600000
500000
400000
Intensity
300000
y = 66202x + 5669.9
R² = 0.9999
200000
100000
0
-1
0
1
2
3
4
5
6
Concentration (ppm)
7
8
9
Mn2+ Analysis
Name of Complex
[Mn(bda)].2H2O
Theoretical
Concentration
(ppm)
5.3
Experimental
Concentration
(ppm)
4.647
[Mn(pda)].H2O
5.36
4.001
[Mn(hxda)].H2O
5
3.468
Drug 1,
[Mn2(bda)2(phen)2(H2O)].2
H2O
Drug 2, [Mn(pda)(phen)]
5.4
9.5
4.75 x 2
5.45
4.325
4.68
1.468
Drug 3,
[Mn(hxda)(phen)2(H2O)].7
H2O
Magnetic Susceptibility
Balance
µ𝑠 .𝑜. =
𝑛(𝑛 + 2)
Where;
N = number of unpaired electrons, n=5
µ𝑠 .𝑜. =
5(5 + 2) = 35 = 5.92
µs.o. = 5.92B.M.
Gram Magnetic Susceptibility
Calculation
c ∗ l ∗ (R − R 0 )
Χg =
109 ∗ m
C= calibration constant, 1.05
L= sample length, cm
R= reading taken of sample
R0 = reading taken with no sample
M= sample mass (g)
Molar Magnetic Susceptibility
𝛸𝑀 = 𝛸𝑔 ∗ 𝑀
Where;
𝛸𝑀 = Molar Magetic Susceptibility
𝛸𝑔 = Gram Magnetic Susceptibility (cm3 g-1)
M= Molar Mass (g mol-1)
Effective Magnetic Moment
µEFF = 2.828 𝑇𝑋𝑀
µEFF = effective magnetic moment, B.M.
T= Temperature (K), 292K
XM = Molar magnetic Susceptibility, cm3 mol-1
Name of Substance
[Mn(bda)].2H2O
Theoretical Value
B.M.
5.92
Experimental
Value B.M.
5.87
[Mn(pda)].H2O
5.92
6.16
[Mn(hxda)].H2O
5.92
3.09
Drug 1,
[Mn2(bda)2(phen)2(H2O)].
2H2O
5.92
8.91
4.455 x 2
Drug 2, [Mn(pda)(phen)]
5.92
6.36
Drug 3,
[Mn(hxda)(phen)2(H2O)].
7H2O
5.92
8.62
Conclusion
1. The complex salt [Mn2(oda)(phen)4(H2O)2]
[Mn2(oda)(phen)4(oda)2]4H2O (MD1) is an excellent lead
candidate for the prevention of α-Synuclein aggregation.
2. Three known analogues of MD1
{[Mn(hxda)(phen)2(H2O)].7H2O; [Mn(pda)(phen)]; and
[Mn2(bda)2(phen)2(H2O)].2H2O along with their precursor
manganese(II) dicarboxylate complexes have been
synthesised using methods previously published
3. All six complexes have been characterised using a range of
analytical techniques.
4. Further work is required to purify the complexes in
preparation for their use in a structure-activity relationship
study.
Acknowledgements
I would like to thank my supervisors Professor Michael
Devereux and Dr. Patricia Ennis for their help and support
when carrying out this project.
I would also like to thank the School of Chemical &
Pharmaceutical Sciences for allowing me to use their
equipment.
Thank You