The most common solid tumors show intrinsic multidrug resistance (MDR) or inevitably acquire suchwhen treated with anticancer drugs. In this work, we describe the discovery of a peripherally restricted, potent, competitive NMDA receptor antagonist 1l by a structure-activity-study of the broad-acting ionotropic glutamate receptor antagonist 1a. Subsequently, we demonstrate that 1l augments the cytotoxic action of sorafenib in murine hepatocellular carcinoma (HCC) cells. The underlying biological mechanism was shown to be interference with the lipid signaling pathway, leading to reduced expression of MDR transporters and therebyan increased accumulation of sorafenib in the cancer cells. Interference with lipid signaling pathwaysby NMDA receptor inhibition is a novel and promising strategy for reversing transporter-mediated chemoresistance in cancer cells.

Pseudopeptide inhibitors of MMP-12 with a phosphinic dipeptide G psi[PO(2)H-CH(2)]L covering the P1-P1'- positions originating from a combinatorial solid phase library have been identified and kinetically analysed with respect to binding mechanism and selectivity towards MMP-7, MMP-9, MMP-13 and MMP-14. One compound with a low nanomolar dissociation constant for MMP-12 showed significantly lower affinity towards all other MMPs tested compared to MMP-12. Two compounds showed selectivity against MMP-9, MMP-13 and MMP-14. One additional compound showed selectivity against MMP-7. The selectivity of these compounds could partly be rationalized by analysis of homology models of the enzymes. Truncated versions of one inhibitor spanning P2 to P2', P3 to P2' or P2 to P3' showed that interactions on both the prime and the non-prime side are important for binding. A two-step binding mechanism, with a rate limiting second step, was shown for binding of a tryptophane containing inhibitor to MMP-12 by transient state analysis, using the tryptophane residue of the inhibitor as fluorescent probe.

A series of analogues of the (S)-2-Amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA) receptor agonist BnTetAMPA (5b) were synthesized and characterized pharmacologically in radioligand binding assays at native and cloned AMPA receptors and functionally by two-electrode voltage clamp electrophysiology at the four homomeric AMPA receptors expressed in Xenopus laevis oocytes. The analogues 6 and 7 exhibit very different pharmacological profiles with binding affinity preference for the subtypes GluA1 and GluA3, respectively. X-ray crystal structures of three ligands (6, 7, and 8) in complex with the agonist binding domain (ABD) of GluA2 show that they induce full domain closure despite their low agonist efficacies. Trp767 in GluA2 ABD could be an important determinant for partial agonism of this compound series at AMPA receptors, since agonist efficacy also correlated with the location of the Trp767 side chain.

Competitive antagonists for ionotropic glutamate receptors (iGluRs) are highly valuable tool compounds for studying health and disease states in the central nervous system. However, only few subtype selective tool compounds are available and the discovery of antagonists with novel iGluR subtype selectivity profiles remains a profound challenge. In this paper, we report an elaborate structure–activity relationship (SAR) study of the parental scaffold 2,3-trans-3-carboxy-3-phenyl-proline by the synthesis of 40 new analogues. Three synthetic strategies were employed with two new strategies of which one being a highly efficient and fully enantioselective strategy based on C­(sp3)–H activation methodology. The SAR study led to the conclusion that selectivity for the NMDA receptors was a general trend when adding substituents in the 5′-position. Selective NMDA receptor antagonists were obtained with high potency (IC50 values as low as 200 nM) and 3–34-fold preference for GluN1/GluN2A over GluN1/GluN2B-D NMDA receptors.

Development of pharmacological tools for the ionotropic glutamate receptors (iGluRs) is imperative for the study and understanding of the role and function of these receptors in the central nervous system. We report the synthesis of 18 analogues of (2S,3R)-2-carboxy-3-pyrrolidine acetic acid (3a), which explores the effect of introducing a substituent on the ε-carbon (3c−q). A new synthetic method was developed for the efficient synthesis of racemic 3a and applied to give expedited access to 13 racemic analogues of 3a. Pharmacological characterization was carried out at native iGluRs, cloned homomeric kainate receptors (GluK1−3), NMDA receptors (GluN1/ GluN2A-D), and excitatory amino acid transporters (EAAT1−3). From the structure−activity relationship studies, several new ligands emerged, exemplified by triazole 3p-d1, GluK3preferring (GluK1/GluK3 K i ratio of 15), and the structurally closely related tetrazole 3q-s3−4 that displayed 4.4−100-fold preference as an antagonist for the GluN1/GluN2A receptor (K i = 0.61 μM) over GluN1/GluN2B-D (K i = 2.7−62 μM).