Chemo-Enzymatic Synthesis of a Series of 2,4-Syn-Functionalized (S)-Glutamate Analogues: New Insight into the Structure−Activity Relation of Ionotropic Glutamate Receptor Subtypes 5, 6, and 7

Abstract

( S)-Glutamic acid (Glu) is the major excitatory neurotransmitter in the central nervous system (CNS) activating the plethora of ionotropic Glu receptors (iGluRs) and metabotropic Glu receptors (mGluRs). In this paper, we present a chemo-enzymatic strategy for the enantioselective synthesis of five new Glu analogues 2a- f ( 2d is exempt) holding a functionalized substituent in the 4-position. Nine Glu analogues 2a- j are characterized pharmacologically at native 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA), kainic acid (KA), and N-methyl- d-aspartic acid (NMDA) receptors in rat synaptosomes as well as in binding assays at cloned rat iGluR5-7 subtypes. A detailed in silico study address as to why 2h is a high-affinity ligand at iGluR5-7 ( K i = 3.81, 123, 57.3 nM, respectively), while 2e is only a high affinity ligand at iGluR5 ( K i = 42.8 nM). Furthermore, a small series of commercially available iGluR ligands are characterized in iGluR5-7 binding.

Binding site and interlobe interactions of the ionotropic glutamate receptor GluK3 ligand binding domain revealed by high resolution crystal structure in complex with (S)-glutamate

“…Overall, the binding mode of glutamate is conserved and similar to other iGluRs (Mayer, 2005;Naur et al, 2005), which is in agreement with its high binding affinity towards full length GluK3 (K i = 494 nM, Sagot et al, 2008). The binding affinity of glutamate for GluK3 LBD was determined to be K i = 7.4 ± 1.6 lM (Fig.…”

“…1C), suggesting that the binding at the GluK3 LBD construct is lower than at the full-length receptor. A difference between the affinities of glutamate at the full length receptor and the isolated LBD is seen also for GluK2; the LBD construct has a K i of 1.4 lM (Mayer, 2005) while K i at the full length receptor is 331 nM (Sagot et al, 2008). The purified GluK1 LBD on the other hand had a similar affinity for glutamate as for full length receptors; K i of 57 nM (Mayer, 2005) and 140 nM (Sagot et al, 2008), respectively.…”

The Glutamate Hypothesis in ALS: Pathophysiology and Drug Development

“…Among ten Glu-analogues assessed for their affinities for human EAAT1-3, enantiomer 3 showed selectivity for EAAT2 (IC 50 of 75 μM for EAAT2, compared to IC 50 >1000 μM for EAAT1 and 3), but a lower affinity for the reference competitive, non-transportable EAAT inhibitor, DL-TBOA. These experiments highlight that extending the R side chain (derivatives 3) results in a selective EAAT2 inhibitor with low affinity for all of the ionotropic GluRs [90,91]. Recently, other glutamate analogues were also characterized pharmacologically using a […”

Glutamate Receptor Ion Channels: Structure, Regulation, and Function

“…Kainate has a 2-carboxypyrrolidine-3-acetic acid backbone, and analogs containing this backbone, known as kainoids (Sonnenberg et al, 1996;Hodgson et al, 2005;Sagot et al, 2008;Bunch and Krogsgaard-Larsen, 2009), include domoic acid (Hampson et al, 1992;Alt et al, 2004) and acromelic acid (Kwak et al, 1992;Smith and McIlhinney, 1992). Agonist potency and efficacy are subunit-specific, because kainate and domoic acid are potent agonists of GluK1 and GluK2 but show low potency at GluK3 receptors (Table 6; Jane et al, 2009).…”