Lennart Bunch

Hydrogenotrophic methanogens are anaerobic archaea that convert carbon dioxide and hydrogen into methane. Central to this process is the heterodisulfide reductase (Hdr), which catalyzes the reduction of the heterodisulfide made of coenzyme M and coenzyme B. In vivo, Hdr functions in association with electron‐donating modules such as the [NiFe]‐hydrogenase (HdrMvh), which supplies reducing equivalents derived from hydrogen oxidation. Here, we isolate the catalytic properties of Hdr by evaluating substrate turnover independently of its native electron‐donating modules using an artificial electron donor system. The molecular features governing substrate recognition and turnover by Hdr were investigated through the design and synthesis of 18 non‐endogenous analogs of the native heterodisulfide substrate (compounds 2a–r ). We show that several non‐endogenous disulfides can serve as alternative substrates for Hdr, including analogs with variation in the coenzyme B‐derived amino acid moiety ( O ‐phosphono‐Ser, L ‐Asp, L ‐Glu, and 2‐aminoadipic acid), and that the coenzyme M sulfonate can be replaced by a carboxylate group. In contrast, modifications that disrupt charge balance, chain length, or stereochemical compatibility result in loss of substrate activity and, in some cases, lead to inhibitory behavior, underscoring the narrow constraints required for productive catalysis.

Enhancing glutamate (Glu) uptake by positive allosteric modulation of excitatory amino acid transporter subtype 2 (EAAT2) is an attractive strategy to enable neuroprotection. However, while the EAAT field is rich in reports on inhibitors, enhancing EAAT2 protein dynamics is a much more difficult objective. A natural product approach reported that a spider venom HPLC fraction, number 10, showed neuroprotective effects. It was referred to as parawixin10, and later the structure of the key component responsible for the neuroprotective action was disclosed to be an N-acylamine, compound 2. We have resynthesized the N-acylamine 2 (parawixin10) and show here that this compound does not enhance Glu uptake in a wide range of radioligand binding assays, nor does it, in our hands, show any neuroprotective effect in a dose-dependent, statistically significant way.

Interconversion of functional groups in organic chemistry is a key task. Here we have developed an oxidative transformation of aldehydes to nitriles using lithium bis(trimethylsilyl)amide as a nitrogen source and copper iodide as an inexpensive catalyst under aerobic and ligand free conditions. The reaction proceeds in 23-98% yield (median of 78%), tolerating various functional groups (22 examples). Furthermore, the reaction was easily scaled to 25 mmol (3.2 g of nitrile product), potentially making it relevant for industry applications.

NMDA receptor ligands have therapeutic potential in neurological and psychiatric disorders. We designed (R)-3-(5-thienyl)carboxamido-2-aminopropanoic acid derivatives with nanomolar agonist potencies at NMDA receptor subtypes (GluN12/A-D). These compounds are superagonists at GluN1/2C compared to glycine and partial to full agonists at GluN1/2A and GluN1/2D but display functional antagonism at GluN1/2B due to low agonist efficacy. Notably, 8d display 864% agonist efficacy at GluN1/2C relative to glycine, and 8j has high potency at GluN1/2A (0.018 μM), GluN1/2C (0.0029 μM), and GluN1/2D (0.016 μM). We evaluated the binding mode in the glycine site using molecular modeling and mutagenesis. In vitro absorption, distribution, metabolism, and excretion (ADME) assays predict high metabolic stability but poor blood-brain barrier permeability. However, an ester prodrug for the carboxylate group of 7j display moderately high blood-brain barrier permeability. The thiophenecarboxamide agonists expand the synthetic pharmacology of NMDA receptors and provide structural insights that facilitate the design of GluN1 agonists with GluN2 subunit-specific activity.

Twenty-one simplified analogues of the natural product domoic acid were designed, synthesized, and then characterized at homomeric kainic acid (KA) receptors (GluK1-3,5). LBG20304 displays a high affinity for homomeric GluK5 receptors (IC50 = 432 nM) with a >40-fold selectivity over homomeric GluK1-3 subtypes and >> 100-fold selectivity over native AMPA and N-methyl d-aspartate receptors. Functional studies of LBG20304 on heteromeric GluK2/5 receptors show no agonist or antagonist functional response at 10 mu M, while a concentration of 100 mu M at neuronal slices (rat) shows low agonist activity. A molecular dynamics simulation of LBG20304, in a homology model of GluK5, suggests specific interactions with the GluK5 receptor and an occluded ligand binding domain, which is translated to agonist or partial agonist activity. LBG20304 is a new compound for the study of the role and function of the KA receptors with the aim of understanding the involvement of these receptors in health and disease.

Metabotropic glutamate (Glu) receptors (mGlu receptors) play a key role in modulating excitatory neurotransmission in the central nervous system (CNS). In this study, we report the structure-based design and pharmacological evaluation of densely functionalized, conformationally restricted glutamate analogue (1S,2S,3S)-2-((S)-amino(carboxy)methyl)-3-(carboxymethyl)cyclopropane-1-carboxylic acid (LBG30300). LBG30300 was synthesized in a stereocontrolled fashion in nine steps from a commercially available optically active epoxide. Functional characterization of all eight mGlu receptor subtypes showed that LBG30300 is a picomolar agonist at mGlu₂ with excellent selectivity over mGlu₃ and the other six mGlu receptor subtypes. Bioavailability studies on mice (IV administration) confirm CNS exposure, and an in silico study predicts a binding mode of LBG30300 which induces a flipping of Tyr144 to allow for a salt bridge interaction of the acetate group with Arg271. The Tyr144 residue now prevents Arg271 from interacting with Asp146, which is a residue of differentiation between mGlu₂ and mGlu₃ and thus could explain the observed subtype selectivity.

Herein we describe a convenient method for the synthesis of the β-substituted Cys analogs 1a, b and trans-β-mercapto proline 1c, from their corresponding α,β-unsaturated-α-amino esters using p-methoxybenzyl mercaptan as the sulfur source. The intermediate β-thioethers are stable toward chromatographic purification, and after global deprotection the β-mercapto amino acids 1a–c are obtained in good to high yields (64%–99%).

The development of tool compounds for the ionotropic glutamate receptors (iGluRs) remains an important research objective, as these are essential for the study and understanding of the roles of these receptors in health and disease. Herein, we report on the pharmacological characterization of (S)-2-hydroxyhistidine (2a) and (S)-2-mercaptohistidine (2b) as mediators of glutamatergic neurotransmission. While 2a displayed negligible binding affinity or activity at all glutamate receptors and transporters investigated, 2b displayed selectivity for homomeric GluK3 with binding affinities in the low micromolar range (K-i = 6.42 +/- 0.74 mu M). The iGluR subtype selectivity ratio for 2b was calculated at similar to 30-fold for GluK1/GluK3, GluA3/GluK3, and GluA4/GluK3 and >100-fold for GluK2/GluK3, GluA1/GluK3, and GluA2/GluK3. Unexpectedly, functional characterization of 2b revealed that the compound is an antagonist (K-b = 7.6 mu M) at homomeric GluK3 receptors while exhibiting only weak agonist activity at GluA2 (EC50 = 3.25 +/- 0.55 mM). The functional properties of 2b were explored further in electrophysiological recordings of mouse hippocampal neurons.

Anilines are key constituents in biologically active compounds and often obtained from transition metal‐catalyzed coupling of an aryl halide with an amine. In this work, we report a transition metal‐free method for the synthesis of meta‐bromo‐ and meta‐trifluoromethylanilines starting from 3‐tribromomethylcyclopentanone or 3‐(2‐bromo‐2‐chloro‐1,1,1‐trifluoroethyl)cyclopentanone, respectively. The scope of the transformation is shown by application of primary, secondary and aromatic amines. The reaction proceeds in acceptable to high yields (20–81 %), and allows for the synthesis of anilines with substitution patterns otherwise difficult to access.