Synthesis and SAR of a series of mGlu7 NAMs based on an ethyl-8-methoxy-4-(4-phenylpiperazin-1-yl)quinoline carboxylate core

Green synthesis and antitumor activity of (E)-diethyl 2-styrylquinoline-3,4-dicarboxylates

In this work, a green, efficient and catalyst-free synthesis of a series of structurally novel (E)-diethyl 2-styrylquinoline-3,4-dicarboxylates via a direct olefination reaction between diethyl 2-methylquinoline-3,4-dicarboxylate and various aromatic aldehydes was successfully accomplished by employing eco-friendly 1,3-dimethylurea/l-(+)-tartaric acid (DMU/LTA) as an inexpensive, non-toxic and reusable reaction medium. This methodology has the attractive advantages of mild reaction conditions, simple experimental operation, and the absence of any dangerous catalysts or unsafe volatile organic solvents, with satisfactory to good yields. Subsequently, a primary in vitro evaluation for their anti-proliferative activity against human cancer cell lines A549, HT29 and T24 revealed that the compound with the 3,4,5-trimethoxystyryl moiety exhibited potent anti-tumor activity with IC50 values of 2.38, 4.52 and 9.86 μmol L-1, respectively, thereby being equipotent or even better than the reference cisplatin.

3-Substituted 6-Azabicyclo[3.1.1]heptanes: Nonclassical Piperidine Isosteres for Drug Discovery

Advanced analogs of piperidine and smaller homologues of tropane─3-substituted 6-azabicyclo[3.1.1]heptanes─were synthesized on a large scale using readily available bulk reagents. The key step of the approach involved the double alkylation reaction of malonate with cis-2,4-bis(mesyloxymethyl)azetidine-1-carboxylate, in turn easily prepared on up to 1 kg scale. After hydrolysis, N-Boc-6-azabicyclo[3.1.1]heptane-3,3-dicarboxylic acid was obtained (up to 400 g in a single run), which was used as a common intermediate for the preparation of all the title building blocks. In particular, Pb(OAc)4-mediated oxidative decarboxylation of this intermediate gave 2,6-methanopiperidone derivative (up to 400 g scale), while monodecarboxylation gave N-Boc-6-azabicyclo[3.1.1]heptane-3-carboxylic acids as an easily separatable mixture of cis and trans diastereomers (up to 100 g scale). Further functional group transformations gave diastereopure cis- and trans-N-Boc-monoprotected diamines and amino alcohols. Molecular structure analysis using exit vector parameters (EVP) revealed that cis isomers of 3-substituted 6-azabicyclo[3.1.1]heptanes are three-dimensional analogs of common 1,4-disubstituted piperidine chair conformer, whereas trans isomers can be considered as unusual "boat" piperidines.

Targeting mGluR group III for the treatment of neurodegenerative diseases

Glutamate, an excitatory neurotransmitter, is essential for neuronal function, and it acts on ionotropic or metabotropic glutamate receptors (mGluRs). A disturbance in glutamatergic signaling is a hallmark of many neurodegenerative diseases. Developing disease-modifying treatments for neurodegenerative diseases targeting glutamate receptors is a promising avenue. The understudied group III mGluR 4, 6-8 are commonly found in the presynaptic membrane, and their activation inhibits glutamate release. Thus, targeted mGluRs therapies could aid in treating neurodegenerative diseases. This review describes group III mGluRs and their pharmacological ligands in the context of amyotrophic lateral sclerosis, Parkinson's, Alzheimer's, and Huntington's diseases. Attempts to evaluate the efficacy of these drugs in clinical trials are also discussed. Despite a growing list of group III mGluR-specific pharmacological ligands, research on the use of these drugs in neurodegenerative diseases is limited, except for Parkinson's disease. Future efforts should focus on delineating the contribution of group III mGluR to neurodegeneration and developing novel ligands with superior efficacy and a favorable side effect profile for the treatment of neurodegenerative diseases.

Differential Activity of Orthosteric Agonists and Allosteric Modulators at Metabotropic Glutamate Receptor 7

Metabotropic glutamate receptor 7 (mGlu7) is a G protein coupled receptor that has demonstrated promise as a therapeutic target across a number of neurologic and psychiatric diseases. Compounds that modulate the activity of mGlu7, such as positive and negative allosteric modulators, may represent new therapeutic strategies to modulate receptor activity. The endogenous neurotransmitter associated with the mGlu receptor family, glutamate, exhibits low efficacy and potency in activating mGlu7, and surrogate agonists, such as the compound L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4), are often used for receptor activation and compound profiling. To understand the implications of the use of such agonists in the development of positive allosteric modulators (PAMs), we performed a systematic evaluation of receptor activation using a system in which mutations can be made in either protomer of the mGlu7 dimer; we employed mutations that prevent interaction with the orthosteric site as well as the G-protein coupling site of the receptor. We then measured increases in calcium levels downstream of a promiscuous G protein to assess the effects of mutations in one of the two protomers in the presence of two different agonists and three positive allosteric modulators. Our results reveal that distinct PAMs, for example N-[3-Chloro-4-[(5-chloro-2-pyridinyl)oxy]phenyl]-2-pyridinecarboxamide (VU0422288) and 3-(2,3-Difluoro-4-methoxyphenyl)-2,5-dimethyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidine (VU6005649), do exhibit different maximal levels of potentiation with L-AP4 versus glutamate, but there appear to be common stable receptor conformations that are shared among all of the compounds examined here. SIGNIFICANCE STATEMENT: This manuscript describes the systematic evaluation of the mGlu7 agonists glutamate and L-(+)-2-Amino-4-phosphonobutyric acid (L-AP4) in the presence and absence of three distinct potentiators examining possible mechanistic differences. These findings demonstrate that mGlu7 potentiators display subtle variances in response to glutamate versus L-AP4.

Persistent challenges in the development of an mGlu7 PAM in vivo tool compound: The discovery of VU6046980

Herein, we report on the further chemical optimization of the first reported mGlu7 positive allosteric modulator (PAM), VU6027459. Replacement of the quinoline core by a cinnoline scaffold increased mGlu7 PAM potency by ∼ 10-fold, and concomitant introduction of a chiral tricyclic motif led to potent mGlu7 PAMs with enantioselective mGlu receptor selectivity profiles. Of these, VU6046980 emerged as a putative in vivo tool compound with excellent CNS penetration (Kp = 4.1; Kp,uu = 0.7) and efficacy in preclinical models. However, either off-target activity at the sigma-1 receptor or activity at a target not elucidated by large ancillary pharmacology panels led to sedation not driven by activation of mGlu7 (validated in Grm7 knockout mice). Thus, despite a significant advance, a viable mGlu7 PAM in vivo tool remains elusive.

Applications of Isosteres of Piperazine in the Design of Biologically Active Compounds: Part 2

Applications of piperazine and homopiperazine in drug design are well-established, and these heterocycles have found use as both scaffolding and terminal elements and also as a means of introducing a water-solubilizing element into a molecule. In the accompanying review (10.1021/acs.jafc.2c00726), we summarized applications of piperazine and homopiperazine and their fused ring homologues in bioactive compound design along with illustrations of the use of 4-substituted piperidines and a sulfoximine-based mimetic. In this review, we discuss applications of pyrrolidine- and fused-pyrrolidine-based mimetics of piperazine and homopiperazine and illustrate derivatives of azetidine that include stretched and spirocyclic motifs, along with applications of a series of diaminocycloalkanes.

Discovery of VU6027459: A First-in-Class Selective and CNS Penetrant mGlu7 Positive Allosteric Modulator Tool Compound

Herein, we report the discovery of the first selective and CNS penetrant mGlu₇ PAM (VU6027459) derived from a "molecular switch" within a selective mGlu₇ NAM chemotype. VU6027459 displayed CNS penetration in both mice (K_p = 2.74) and rats (K_p= 4.78), it was orally bioavailable in rats (%F = 69.5), and undesired activity at DAT was ablated.