Synthesis and Pharmacological Evaluation of 5-Hydroxy-2-(2- phenylethyll)chromone Analogues

Kalamazoo College, Kalamazoo MI

Investigators

Abstract

(7) PROJECT SUMMARY/ ABSTRACT: Glutamate (Glu) is a key excitatory neurotransmitter of the central nervous system (CNS) and plays a significant role in synaptic plasticity, learning and memory. When synaptic concentrations of Glu increase beyond 1μM, overstimulation of Glu receptors initiates an irregular rise in intracellular calcium leading to a cascade of negative cellular responses resulting in neuron death. This process is formally known as glutamate excitotoxicity. Glutamate excitotoxicity has been shown to be a common pathology in glaucoma, amyotrophic lateral sclerosis, and Alzheimer’s, Parkinson’s, and Huntington’s disease. As such, approaches designed to prevent glutamate excitotoxicity would be beneficial for the treatment of many neurodegenerative disorders. 5-Hydroxy-2-(2- phenylethyl)chromone (5-HPEC) was shown to prevent glutamate excitotoxicity; however, its mechanism of action is unknown. Studies from our lab have revealed for the first time that 5-HPEC can act as a low affinity 5- HT2B antagonist and significantly reduces neuronal loss in a Caenorhabditis elegans (C. elegans) model of glutamate excitotoxity. The hypothesis for this proposal is the 5-HPEC scaffold can be used to design and develop selective and potent 5-HT2B antagonists with improved neuroprotective activity against glutamate induced excitotoxicity. Two aims have been proposed to test this hypothesis. Aim 1: Design, synthesize and characterize 5-hydroxy-2-(3-phenylpropyl)chromone analogues as 5-HT2B receptor antagonists. Preliminary structure activity relationship studies showed C-2 alkyl chain homologation of 5-HPEC to 5-hydroxy-2-(3-phenylpropyl)chromone (5-HPPC) improves affinity at 5-HT2B 10 fold. Ligand docking studies of 5-HPPC using the available 5-HT2B crystal structure identified six positions on the 5-HPPC scaffold most likely to influence binding affinity. Aim 1A is to synthesize 40 new analogues based on results from the molecular modeling studies. Synthetic routes executable by undergraduates have been devised to obtain the proposed analogues. Aim 1B will determine the affinity, selectivity, and functional activity for these compounds at 5-HT2B. For compounds with improved receptor pharmacology over 5-HPPC further assays will be used to characterize them as agonist, partial agonist, or antagonist at 5-HT2B. Aim 2: Determine neuroprotective activity of the newly synthesized ligands. Using an established C. elegans model of glutamate excitotoxicity we were able to show administration of 5-HPEC at 22mM significantly reduces neuronal loss due to glutamate excitotoxicity. The goal of this aim is to examine the neuroprotective activity of the synthesized compounds in these animals. In Aim 2A the average number of necrotic head neurons per animal will be determined using differential interference contrast microscopy. In Aim 2B differences in locomotor activity due to neuronal loss between treated and untreated animals will be compared. Compounds showing improved ligand pharmacology at 5-HT2B should reduce neuronal loss and improve locomotor activity.