Azetidinic amino acids: stereocontrolled synthesis and pharmacological characterization as ligands for glutamate receptors and transporters

• Published in: Organic & biomolecular chemistry 2005-11, Vol.3 (21), p.3926-3936
• Main Authors: Bräuner-Osborne, Hans, Bunch, Lennart, Chopin, Nathalie, Couty, François, Evano, Gwilherm, Jensen, Anders A, Kusk, Mie, Nielsen, Birgitte, Rabasso, Nicolas
• Format: Article
• Language: English
• Subjects: Amino Acid Transport System X-AG - metabolism; Amino Acids; Animals; Azetidines - chemical synthesis; Azetidines - pharmacology; Cyclization; Humans; Ligands; Protein Binding; Receptors, Glutamate - metabolism; Receptors, Metabotropic Glutamate - metabolism; Stereoisomerism; Structure-Activity Relationship
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/b509514j

A set of ten azetidinic amino acids, that can be envisioned as C-4 alkyl substituted analogues of trans-2-carboxyazetidine-3-acetic acid (t-CAA) and/or conformationally constrained analogues of (R)- or (S)-glutamic acid (Glu) have been synthesized in a diastereo- and enantiomerically pure form from beta-amino alcohols through a straightforward five step sequence. The key step of this synthesis is an original anionic 4-exo-tet ring closure that forms the azetidine ring upon an intramolecular Michael addition. This reaction was proven to be reversible and to lead to a thermodynamic distribution of two diastereoisomers that were easily separated and converted in two steps into azetidinic amino acids. Azetidines 35-44 were characterized in binding studies on native ionotropic Glu receptors and in functional assays at cloned metabotropic receptors mGluR1, 2 and 4, representing group I, II and III mGlu receptors, respectively. Furthermore, azetidine analogues 35, 36, and 40 were also characterized as potential ligands at the glutamate transporter subtypes EAAT1-3 in the FLIPR Membrane Potential (FMP) assay. The (2R)-azetidines 35, 37, 39, 41 and 43 were inactive in iGlu, mGlu and EAAT assays, whereas a marked change in the pharmacological profile at the iGlu receptors was observed when a methyl group was introduced in the C-4 position, compound 36 versus t-CAA. At EAAT1-3, compound 35 was inactive, whereas azetidines 36 and 40 were both identified as inhibitors and showed selectivity for the EAAT2 subtype.