Synthesis of novel vanillin derivatives: study of their antioxidant and potential neuroprotective properties.

Scipioni, Matteo

Abstract

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is a naturally-occurring phenolic compound, forming the main component of the bean and pod of vanilla orchids. It is widely used as a flavouring agent in food and drinks, and as a preservative in the cosmetic and pharmaceutical industries. In the past decades, several studies have reported on the antioxidant and protective effects of vanillin in several oxidative stress models, both in vitro and in vivo. The aim of this thesis was to synthesise novel vanillin derivatives with enhanced antioxidant properties and to study their potential neuroprotective activities in oxidative stress models in vitro. To achieve this aim, novel vanillin derivatives were synthesised through a reductive amination reaction, by reacting vanillin with a selection of amines. All the derivatives were characterized using 1H and 13C nuclear magnetic resonance and mass spectrometry. The vanillin derivatives were tested in several antioxidant assays with different mechanisms of action, in order to identify the functionalities that contributed to the antioxidant properties of this novel class of compounds. A structure-activity relationship (SAR) was therefore determined. The tetramer 4c turned out to be the most efficient antioxidant in all the assays. The latter compound consists of four vanillin moieties, together with a molecular structure that facilitates electron delocalisation for enhanced antioxidant activity. Selected based on their chemical structures and antioxidant properties, various vanillin derivatives were tested as potential multi-target-directed ligands (MTDLs), for use in the treatment of Alzheimer's disease (AD) - a multifactorial neurodegenerative disease. For this reason, the vanillin derivatives were tested for their ability to inhibit both the acetylcholinesterase (AChE) enzyme and the self-mediated A-beta(1-42) aggregation. The monomer 1f displayed the best inhibitory activities in both respects, with IC50 values at micro-M concentrations. In silico studies were performed in order to identify the molecular elements involved in the AChE inhibitory activities and to predict the ability of selected compounds to cross the blood-brain-barrier (BBB), which is of critical importance when targeting neurodegenerative diseases. Monomer 1f was predicted to be able to cross the BBB. Following this - and this time selected based on their antioxidant and AChE and amyloid inhibitory activities - another group of vanillin derivatives was then tested in oxidative stress models, by applying hydrogen peroxide or a mixture of rotenone/oligomycin A as stressors, in a neuroblastoma SH-SY5Y cell line. Vanillin derivatives showed cellular protective effects, for example by increasing cell viability and reducing reactive oxygen species (ROS) production. However, they were unable to protect the cells' DNA from oxidative damage. Again, compound 4c displayed the most efficient protective effects at micromolar concentrations. Finally, in order to study the mechanism behind the protective effects of 4c in SH-SY5Y cell line, research focused on its ability to activate the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway, which is known to be a predominant mediator of cellular antioxidant response. Since no Nrf2 was observed in the nucleus, this confirms that there must be an alternative mechanism for the antioxidant activity of 4c. Overall, compounds 1f and 4c showed promise for their further development with the potential to assist in the treatment of AD.

Citation

SCIPIONI, M. 2019. Synthesis of novel vanillin derivatives: study of their antioxidant and potential neuroprotective properties. Robert Gordon University [online], PhD thesis. Available from: https://openair.rgu.ac.uk

• Thesis Type: Thesis
• Deposit Date: Jan 28, 2020
• Publicly Available Date: Jan 28, 2020
• Keywords: Vanillin; Antioxidants; Alzheimer's disease; Neurodegeneration; Oxidative stress
• Public URL: https://rgu-repository.worktribe.com/output/841956
• Award Date: Sep 30, 2019