Transcription factors HB21/40/53 trigger inflorescence arrest through abscisic acid accumulation at the end of flowering.

Flowers, and hence, fruits and seeds, are produced by the activity of the inflorescence meristem after the floral transition. In plants with indeterminate inflorescences the final number of flowers produced by the inflorescence meristem is determined by the length of the flowering period, which ends with inflorescence arrest. Inflorescence arrest depends on many different factors, such as the presence of seeds, the influence of the environment, or endogenous factors such as phytohormone levels and age, which modulate inflorescence meristem activity. The FRUITFULL-APETALA2 (FUL-AP2) pathway plays a major role in regulating the end of flowering, likely integrating both endogenous cues and those related to seed formation. Among AP2 targets, HOMEOBOX PROTEIN21 (HB21) has been identified as a putative mediator of AP2 function in the control of inflorescence arrest. HB21 is a homeodomain leucine zipper transcription factor involved in establishing axillary bud dormancy. Here we characterized the role of HB21 in the control of the inflorescence arrest at the end of flowering in Arabidopsis (Arabidopsis thaliana). HB21, together with HB40 and HB53, are upregulated in the inflorescence apex at the end of flowering, promoting floral bud arrest. We also show that abscisic acid (ABA) accumulation occurs in the inflorescence apex in an HB-dependent manner. Our work suggests a physiological role of ABA in floral bud arrest at the end of flowering, pointing to ABA as a regulator of inflorescence arrest downstream of the HB21/40/53 genes.

Investigation of the Compatibility between Warheads and Peptidomimetic Sequences of Protease Inhibitors-A Comprehensive Reactivity and Selectivity Study.

Covalent peptidomimetic protease inhibitors have gained a lot of attention in drug development in recent years. They are designed to covalently bind the catalytically active amino acids through electrophilic groups called warheads. Covalent inhibition has an advantage in terms of pharmacodynamic properties but can also bear toxicity risks due to non-selective off-target protein binding. Therefore, the right combination of a reactive warhead with a well-suited peptidomimetic sequence is of great importance. Herein, the selectivities of well-known warheads combined with peptidomimetic sequences suited for five different proteases were investigated, highlighting the impact of both structure parts (warhead and peptidomimetic sequence) for affinity and selectivity. Molecular docking gave insights into the predicted binding modes of the inhibitors inside the binding pockets of the different enzymes. Moreover, the warheads were investigated by NMR and LC-MS reactivity assays against serine/threonine and cysteine nucleophile models, as well as by quantum mechanics simulations.

Advances in the Development of SARS-CoV-2 Mpro Inhibitors.

Since the outbreak of COVID-19, one of the strategies used to search for new drugs has been to find inhibitors of the main protease (Mpro) of the virus SARS-CoV-2. Initially, previously reported inhibitors of related proteases such as the main proteases of SARS-CoV and MERS-CoV were tested. A huge effort was then carried out by the scientific community to design, synthesize and test new small molecules acting as inactivators of SARS-CoV-2 Mpro. From the chemical structure view, these compounds can be classified into two main groups: one corresponds to modified peptides displaying an adequate sequence for high affinity and a reactive warhead; and the second is a diverse group including chemical compounds that do not have a peptide framework. Although a drug including a SARS-CoV-2 main protease inhibitor has already been commercialized, denoting the importance of this field, more compounds have been demonstrated to be promising potent inhibitors as potential antiviral drugs.

Elucidating the Dual Mode of Action of Dipeptidyl Enoates in the Inhibition of Rhodesain Cysteine Proteases.

A computational study of the two possible inhibition mechanisms of rhodesain cysteine protease by the dipeptidyl enoate Cbz-Phe-Leu-CH=CH-CO2 C2 H5 has been carried out by means of molecular dynamics simulations with hybrid QM/MM potentials. The low free energy barriers confirm that the Cys25 residue can attack both Cß and C1 atoms of the inhibitor, confirming a dual mode of action in the inhibition of the rhodesain by enoates. According to the results, the inhibition process through the Cys25 attack on the Cß atom of the inhibitor is an exergonic and irreversible process, while the inhibition process when Cys25 attacks on the C1 atom of the inhibitor is and exergonic but reversible process. The interactions between the inhibitor and rhodesain suggest that P2 is the most important fragment to consider in the design of new efficient inhibitors of rhodesain. These results may be useful for the design of new inhibitors of rhodesain and other related cysteine proteases based on dipeptidyl enoates scaffolds.

Quantum Mechanics/Molecular Mechanics Studies of the Mechanism of Cysteine Proteases Inhibition by Dipeptidyl Nitroalkenes.

In this work a computational study of the mechanism of inhibition of cruzain, rhodesain, and cathepsin L cysteine proteases by the dipeptidyl nitroalkene Cbz-Phe-Ala-CH=CH-NO2 has been carried out by means of molecular dynamics simulations with hybrid QM/MM potentials. The free-energy surfaces confirmed that the inhibition takes place by the formation of a covalent bond between the protein and the ß-carbon atom of the inhibitor. According to the results, the tested inhibitor should be a much more efficient inhibitor of cruzain than of rhodesain, and little activity would be expected against cathepsin L, in total correspondence with the available experimental data. The origin of these differences may lie in the different stabilizing electrostatic interactions established between the inhibitor and the residues of the active site and S2 pocket of these enzymes. These results may be useful for the rational design of new dipeptidyl nitroalkenes with higher and more selective inhibitory activity against cysteine proteases.

Formal [3+2] Cycloaddition Reactions of Electron-Rich Aryl Epoxides with Alkenes under Lewis Acid Catalysis Affording Tetrasubstituted Tetrahydrofurans.

We report on the regio- and stereoselective synthesis of tetrahydrofurans by reaction between epoxides and alkenes in the presence of a Lewis acid. This is an unprecedented formal [3+2] cycloaddition reaction between an epoxide and an alkene. The chemical reaction represents a very concise synthesis of tetrahydrofurans from accessible starting compounds.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-7.

Breakthroughs in Medicinal Chemistry [...].

Regioselective Opening of Nitroepoxides with Unsymmetrical Diamines.

Nitroepoxides are easily transformed into benzodiazepines, tetrahydrobenzodiazepines, imidazopyridines, and N-alkyl tetrahydroquinoxalines by treatment with 2-aminobenzylamines, 2-aminopyridines, and N-alkyl 1,2-diaminobenzenes, respectively. Regioselectivity is controlled through attack of the most nucleophilic nitrogen of the unsymmetrical diamine to the ß position of the epoxide. These reactions represent an efficient way to prepare privileged bioactive structures.

Antiprotozoal and cysteine proteases inhibitory activity of dipeptidyl enoates.

A family of dipeptidyl enoates has been prepared and tested against the parasitic cysteine proteases rhodesain, cruzain and falcipain-2 related to sleeping sickness, Chagas disease and malaria, respectively. They have also been tested against human cathepsins B and L1 for selectivity. Dipeptidyl enoates resulted to be irreversible inhibitors of these enzymes. Some of the members of the family are very potent inhibitors of parasitic cysteine proteases displaying k2nd (M-1s-1) values of seven orders of magnitude. In vivo antiprotozoal testing was also performed. Inhibitors exhibited IC50 values in the micromolar range against Plasmodium falciparum, Trypanosoma brucei, Trypanosoma cruzi and even more promising lower values against Leishmania donovanii.

Quantum mechanics/molecular mechanics studies of the mechanism of cysteine protease inhibition by peptidyl-2,3-epoxyketones.

Cysteine proteases are the most abundant proteases in parasitic protozoa and they are essential enzymes to the life cycle of several of them, thus becoming attractive therapeutic targets for the development of new inhibitors. In this paper, a computational study of the inhibition mechanism of cysteine protease by dipeptidyl-2,3-epoxyketone Cbz-Phe-Hph-(S), a recently proposed inhibitor, has been carried out by means of molecular dynamics (MD) simulations with hybrid QM/MM potentials. The computed free energy surfaces of the inhibition mechanism of cysteine proteases by peptidyl epoxyketones showing how the activation of the epoxide ring and the attack of Cys25 on either C2 or C3 atoms take place in a concerted manner. According to our results, the acid species responsible for the protonation of the oxygen atom of the ring would be able to conserve His159, in contrast to previous studies that proposed a water molecule as the activating species. The low activation free energies for the reaction where Cys25 attacks the C2 atom of the epoxide ring (12.1 kcal mol-1) or to the C3 atom (15.4 kcal mol-1), together with the high negative reaction energies suggest that the derivatives of peptidyl-2,3-epoxyketones can be used to develop new potent inhibitors for the treatment of Chagas disease.

Synthetic Studies on the Preparation of Alanyl Epoxysulfones as Cathepsin Cysteine Protease Electrophilic Traps.

A Darzens reaction between tert-butoxycarbonyl alaninal and chloromethyl phenyl sulfone afforded chlorohydrins, which were converted into epoxysulfones by reaction with sodium tert-butoxide. Epoxysulfone 10 and chloroketone 14 derived from chlorohydrins by oxidation proved to be inhibitors of cathepsins H, S, and C as determined by competitive activity-based protein profiling.

A novel p38 MAPK docking-groove-targeted compound is a potent inhibitor of inflammatory hyperalgesia.

The MAPK (mitogen-activated protein kinase) p38 is an important mediator of inflammation and of inflammatory and neuropathic pain. We have described recently that docking-groove-dependent interactions are important for p38 MAPK-mediated signal transduction. Thus virtual screening was performed to identify putative docking-groove-targeted p38 MAPK inhibitors. Several compounds of the benzo-oxadiazol family were identified with low micromolar inhibitory activity both in a p38 MAPK activity assay, and in THP-1 human monocytes acting as inhibitors of LPS (lipopolysaccharide)-induced TNFα (tumour necrosis factor α) secretion. Positions 2 and 5 in the phenyl ring are essential for the described inhibitory activity with a chloride in position 5 and a methyl group in position 2 yielding the best results, giving an IC50 value of 1.8 µM (FGA-19 compound). Notably, FGA-19 exerted a potent and long-lasting analgesic effect in vivo when tested in a mouse model of inflammatory hyperalgesia. A single intrathecal injection of FGA-19 completely resolved hyperalgesia, being 10-fold as potent and displaying longer lasting effects than the established p38 MAPK inhibitor SB239063. FGA-19 also reversed persistent pain in a model of post-inflammatory hyperalgesia in LysM (lysozyme M)-GRK2 (G-protein-coupled-receptor kinase)(+/-) mice. These potent in vivo effects suggested p38 MAPK docking-site-targeted inhibitors as a potential novel strategy for the treatment of inflammatory pain.

Peptidyl nitroalkene inhibitors of main protease rationalized by computational and crystallographic investigations as antivirals against SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic continues to represent a global public health issue. The viral main protease (Mpro) represents one of the most attractive targets for the development of antiviral drugs. Herein we report peptidyl nitroalkenes exhibiting enzyme inhibitory activity against Mpro (Ki: 1-10 µM) good anti-SARS-CoV-2 infection activity in the low micromolar range (EC50: 1-12 µM) without significant toxicity. Additional kinetic studies of compounds FGA145, FGA146 and FGA147 show that all three compounds inhibit cathepsin L, denoting a possible multitarget effect of these compounds in the antiviral activity. Structural analysis shows the binding mode of FGA146 and FGA147 to the active site of the protein. Furthermore, our results illustrate that peptidyl nitroalkenes are effective covalent reversible inhibitors of the Mpro and cathepsin L, and that inhibitors FGA145, FGA146 and FGA147 prevent infection against SARS-CoV-2.

Dynamic kinetic asymmetric ring-opening/reductive amination sequence of racemic nitroepoxides with chiral amines: enantioselective synthesis of chiral vicinal diamines.

We report a highly diastereoselective synthesis of vicinal diamines by the treatment of nitroepoxides with primary amines and then a reducing agent. When using a chiral primary amine, racemic nitroepoxides are transformed into chiral diamines as a single enantiomers (>95:5 er) through a dynamic kinetic asymmetric transformation (DYKAT). The overall process is a one-pot procedure combining the exposure of nitroepoxides to chiral amines to afford diastereomeric mixtures of aminoimines and subsequent stereoselective imine reduction.

Impact of the Recognition Part of Dipeptidyl Nitroalkene Compounds on the Inhibition Mechanism of Cysteine Proteases Cruzain and Cathepsin L.

Cysteine proteases (CPs) are an important class of enzymes, many of which are responsible for several human diseases. For instance, cruzain of protozoan parasite Trypanosoma cruzi is responsible for the Chagas disease, while the role of human cathepsin L is associated with some cancers or is a potential target for the treatment of COVID-19. However, despite paramount work carried out during the past years, the compounds that have been proposed so far show limited inhibitory action against these enzymes. We present a study of proposed covalent inhibitors of these two CPs, cruzain and cathepsin L, based on the design, synthesis, kinetic measurements, and QM/MM computational simulations on dipeptidyl nitroalkene compounds. The experimentally determined inhibition data, together with the analysis and the predicted inhibition constants derived from the free energy landscape of the full inhibition process, allowed describing the impact of the recognition part of these compounds and, in particular, the modifications on the P2 site. The designed compounds and, in particular, the one with a bulky group (Trp) at the P2 site show promising in vitro inhibition activities against cruzain and cathepsin L for use as a starting lead compound in the development of drugs with medical applications for the treatment of human diseases and future designs.

Impact of the Warhead of Dipeptidyl Keto Michael Acceptors on the Inhibition Mechanism of Cysteine Protease Cathepsin L.

Cathepsin L (CatL) is a lysosomal cysteine protease whose activity has been related to several human pathologies. However, although preclinical trials using CatL inhibitors were promising, clinical trials have been unsuccessful up to now. We are presenting a study of two designed dipeptidyl keto Michael acceptor potential inhibitors of CatL with either a keto vinyl ester or a keto vinyl sulfone (KVS) warhead. The compounds were synthesized and experimentally assayed in vitro, and their inhibition molecular mechanism was explored based on molecular dynamics simulations at the density functional theory/molecular mechanics level. The results confirm that both compounds inhibit CatL in the nanomolar range and show a time-dependent inhibition. Interestingly, despite both presenting almost equivalent equilibrium constants for the reversible formation of the noncovalent enzyme/inhibitor complex, differences are observed in the chemical step corresponding to the enzyme-inhibitor covalent bond formation, results that are mirrored by the computer simulations. Theoretically determined kinetic and thermodynamic results, which are in very good agreement with the experiments, afford a detailed explanation of the relevance of the different structural features of both compounds having a significant impact on enzyme inhibition. The unprecedented binding interactions of both inhibitors in the P1' site of CatL represent valuable information for the design of inhibitors. In particular, the peptidyl KVS can be used as a starting lead compound in the development of drugs with medical applications for the treatment of cancerous pathologies since sulfone warheads have previously shown promising cell stability compared to other functions such as carboxylic esters. Future improvements can be guided by the atomistic description of the enzyme-inhibitor interactions established along the inhibition reaction derived from computer simulations.

Radical mechanism in the elimination of 2-arylsulfinyl esters.

The mechanism of the dehydrosulfenylation of 2-arylsulfinyl esters was investigated. The reaction was found to follow a homolytic cleavage mechanism as verified by electrospray ionization tandem mass spectrometry and experimental work. Rearranged sulfoxides are obtained as byproduct during the elimination reaction.

Stereoisomerization of beta-hydroxy-alpha-sulfenyl-gamma-butyrolactones controlled by two concomitant 1,4-type nonbonded sulfur-oxygen interactions as analyzed by X-ray crystallography.

We have synthesized nine beta-hydroxy-alpha-sulfenyl-gamma-butyrolactones having different substituents. The syn-anti or syn-syn lactones (or any mixture of both) invariably isomerized into syn-anti/syn-syn lactones in a ratio of approximately 6/4. The other two possible isomeric lactones (anti-syn or anti-anti) were never observed. The crystal structures of syn-syn lactones have been determined. We found sulfur-oxygen distances to be less than the sum of the van der Waals radii (3.3 A), with the angle formed among the hydroxylic oxygen, sulfur, and quaternary aromatic carbon being close to 180 degrees. In addition, carbonylic oxygen-sulfur is directed <40 degrees from the perpendicular to the C-S-C. Theoretical calculations were performed which emphasize the directionality of the sulfur-oxygen interaction. The X-ray and theoretical studies demonstrate that two concomitant, attractive 1,4 intramolecular interactions of divalent sulfur with both carbonyl and hydroxyl oxygens are the driving force for the aforementioned stereochemical preference. Then nonbonded sulfur-oxygen interactions would control the stereoselectivity of the reaction. The same features are observed in the X-ray structure of a beta-hydroxy-alpha-sulfinyl-gamma-butyrolactone.

Mechanism of inhibition of SARS-CoV-2 Mpro by N3 peptidyl Michael acceptor explained by QM/MM simulations and design of new derivatives with tunable chemical reactivity.

The SARS-CoV-2 main protease (Mpro) is essential for replication of the virus responsible for the COVID-19 pandemic, and one of the main targets for drug design. Here, we simulate the inhibition process of SARS-CoV-2 Mpro with a known Michael acceptor (peptidyl) inhibitor, N3. The free energy landscape for the mechanism of the formation of the covalent enzyme-inhibitor product is computed with QM/MM molecular dynamics methods. The simulations show a two-step mechanism, and give structures and calculated barriers in good agreement with experiment. Using these results and information from our previous investigation on the proteolysis reaction of SARS-CoV-2 Mpro, we design two new, synthetically accessible N3-analogues as potential inhibitors, in which the recognition and warhead motifs are modified. QM/MM modelling of the mechanism of inhibition of Mpro by these novel compounds indicates that both may be promising candidates as drug leads against COVID-19, one as an irreversible inhibitor and one as a potential reversible inhibitor.

Three-Step Telescoped Synthesis of Monosubstituted Vicinal Diamines from Aldehydes.

Aldehydes are easily transformed into vicinal diamines and piperazines through a one-pot procedure including a Darzens reaction and treatment with an amine or diamine and then with a reducing agent. Additionally, quinoxalines can be accessed by reaction with 1,2-benzenediamine under oxidative conditions. These transformations are simple methods for the preparation of synthetically interesting monosubstituted diamines, piperazines, and quinoxalines.