Chemoproteomic Profiling by Cysteine Fluoroalkylation Reveals Myrocin G as an Inhibitor of the Nonhomologous End Joining DNA Repair Pathway.

Chemoproteomic profiling of cysteines has emerged as a powerful method for screening the proteome-wide targets of cysteine-reactive fragments, drugs, and natural products. Herein, we report the development and an in-depth evaluation of a tetrafluoroalkyl benziodoxole (TFBX) as a cysteine-selective chemoproteomic probe. We show that this probe features numerous key improvements compared to the traditionally used cysteine-reactive probes, including a superior target occupancy, faster labeling kinetics, and broader proteomic coverage, thus enabling profiling of cysteines directly in live cells. In addition, the fluorine "signature" of probe 7 constitutes an additional advantage resulting in a more confident adduct-amino acid site assignment in mass-spectrometry-based identification workflows. We demonstrate the utility of our new probe for proteome-wide target profiling by identifying the cellular targets of (-)-myrocin G, an antiproliferative fungal natural product with a to-date unknown mechanism of action. We show that this natural product and a simplified analogue target the X-ray repair cross-complementing protein 5 (XRCC5), an ATP-dependent DNA helicase that primes DNA repair machinery for nonhomologous end joining (NHEJ) upon DNA double-strand breaks, making them the first reported inhibitors of this biomedically highly important protein. We further demonstrate that myrocins disrupt the interaction of XRCC5 with DNA leading to sensitization of cancer cells to the chemotherapeutic agent etoposide as well as UV-light-induced DNA damage. Altogether, our next-generation cysteine-reactive probe enables broader and deeper profiling of the cysteinome, rendering it a highly attractive tool for elucidation of targets of electrophilic small molecules.

Increased Potency and Selectivity for Group III Metabotropic Glutamate Receptor Agonists Binding at Dual sites.

A group III metabotropic glutamate (mGlu) receptor agonist (PCEP) was identified by virtual HTS. This orthosteric ligand is composed by an l-AP4-derived fragment that mimics glutamate and a chain that binds into a neighboring pocket, offering possibilities to improve affinity and selectivity. Herein we describe a series of derivatives where the distal chain is replaced by an aromatic or heteroaromatic group. Potent agonists were identified, including some with a mGlu4 subtype preference, e.g., 17m (LSP1-2111) and 16g (LSP4-2022). Molecular modeling suggests that aromatic functional groups may bind at either one of the two chloride regulatory sites. These agonists may thus be considered as particular bitopic/dualsteric ligands. 17m was shown to reduce GABAergic synaptic transmission at striatopallidal synapses. We now demonstrate its inhibitory effect at glutamatergic parallel fiber-Purkinje cell synapses in the cerebellar cortex. Although these ligands have physicochemical properties that are markedly different from typical CNS drugs, they hold significant therapeutic potential.

Synthesis of Mono- and Bis(fluoroalkyl)pyrimidines from FARs, Fluorinated Acetoacetates, and Malononitrile Provides Easy Access to Novel High-Value Pyrimidine Scaffolds.

A new strategy was developed using fluorinated acetoacetates, malononitrile, and fluoroalkyl amino reagents (FARs) to access unprecedented 4,6-bis(fluoroalkyl)pyrimidine-5-carboxylates, their carboxylic acid analogues, and 4-amino-6-(fluoroalkyl)pyrimidine-5-carbonitriles. An efficient cyclization step using suitable amidines was developed under microwave irradiation, providing the desired pyrimidines rapidly and efficiently. Standard saponification conditions were applied from carboxylate derivatives to access to the corresponding carboxylic acids. These new valuable building blocks, bearing either a single or two emergent fluorinated substituents, hold strong potential for medicinal and agrochemical research.

Fluoroalkyl Amino Reagents (FARs): A General Approach towards the Synthesis of Heterocyclic Compounds Bearing Emergent Fluorinated Substituents.

Fluorinated heterocycles are important building blocks in pharmaceutical, agrochemical and material sciences. Therefore, organofluorine chemistry has witnessed high interest in the development of efficient methods for the introduction of emergent fluorinated substituents (EFS) onto heterocycles. In this context, fluoroalkyl amino reagents (FARs)-a class of chemicals that was slightly forgotten over the last decades-has emerged again recently and proved to be a powerful tool for the introduction of various fluorinated groups onto (hetero)aromatic derivatives.

Determination of the absolute configuration of phosphinic analogues of glutamate.

A series of phosphinic glutamate derivatives (e.g.LSP1-2111) have been proven to be potent agonists of metabotropic glutamate (mGlu) receptors and shown promising in vivo activity. However, so far all were synthesized and tested as a mixture of two diastereomers whose absolute and relative configurations are not known. In this study, the stereomers were separated on a Crownpack CR(+) column and their absolute configuration was assessed by means of a diastereoselective synthesis. Both separated L-stereomers activated the mGlu4 receptor with EC50's of 0.72 and 4.4 µM for (1S,1'S)-and (1S,1'R)-LSP1-2111, respectively.