Azetidinic amino acids: stereocontrolled synthesis and pharmacological characterization as ligands for glutamate receptors and transporters.
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.
Bräuner-Osborne
Hans
H
Department of Medicinal Chemistry, Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100, Copenhagen, Denmark.
Bunch
Lennart
L
Chopin
Nathalie
N
Couty
François
F
Evano
Gwilherm
G
Jensen
Anders A
AA
Kusk
Mie
M
Nielsen
Birgitte
B
Rabasso
Nicolas
N
D027322:Amino Acid Transport System X-AG / Q000378:metabolism*; D000596:Amino Acids; D000818:Animals; D001384:Azetidines / Q000138:chemical synthesis* / Q000494:pharmacology*; D003500:Cyclization; D006801:Humans; D008024:Ligands; D011485:Protein Binding; D017470:Receptors, Glutamate / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D027322:Amino Acid Transport System X-AG; D000596:Amino Acids; D001384:Azetidines; D008024:Ligands; D017470:Receptors, Glutamate; D018094:Receptors, Metabotropic Glutamate; C108822:metabotropic glutamate receptor 2; C102718:metabotropic glutamate receptor 3; C104077:metabotropic glutamate receptor type 1; C108823:metabotropic glutamate receptor 4