Development of serine protease inhibitors displaying a multicentered short (<2.3 A) hydrogen bond binding mode: inhibitors of urokinase-type plasminogen activator and factor Xa

Exploring Photoswitchable Binding Interactions with Small-Molecule- and Peptide-Based Inhibitors of Trypsin

The ability to photochemically activate a drug, both when and where needed, requires optimisation of the difference in biological activity between each isomeric state. As a step to this goal, we report small-molecule- and peptide-based inhibitors of the same protease-trypsin-to better understand how photoswitchable drugs interact with their biological target. The best peptidic inhibitor displayed a more than fivefold difference in inhibitory activity between isomeric states, whereas the best small-molecule inhibitor only showed a 3.4-fold difference. Docking and molecular modelling suggest this result is due to a large change in 3D structure in the key binding residues of the peptidic inhibitor upon isomerisation; this is not observed for the small-molecule inhibitor. Hence, we demonstrate that significant structural changes in critical binding motifs upon irradiation are essential for maximising the difference in biological activity between isomeric states. This is an important consideration in the design of future photoswitchable drugs for clinical applications.

Recognition-Induced Enhanced Emission of Core-Fluorescent ESIPT-type Macrocycles

Core-fluorescent cavitands based on 2-(2'-resorcinol)benzimidazole fluorophores (RBIs) merged with the resorcin[4]arene skeleton were designed and synthesized. The cavitands, due to the presence of intramolecular hydrogen bonds and increased acidity, show excited state intramolecular proton transfer (ESIPT) and readily undergo deprotonation to form dianionic cavitands, capable of strong binding to organic cations. The changes in fluorescence are induced by deprotonation and binding events and involve huge Stokes shifts (due to emission from anionic double keto tautomers) and cation-selective enhancement of emission originating from the restriction of intramolecular motion (RIR) upon recognition in the cavity. Ab initio calculations indicate that the macrocyclic scaffold stabilizes the ground state tautomeric forms of the fluorophores that are not observed for non-macrocyclic analogs. In the excited state, the emitting forms for both macrocyclic scaffolds and non-macrocyclic analogs are anionic double keto tautomers, which are the result of excited state intramolecular proton transfer (ESIPT) or excited state double proton transfer (ESDPT).

Urokinase plasminogen activator as an anti-metastasis target: inhibitor design principles, recent amiloride derivatives, and issues with human/mouse species selectivity

The urokinase plasminogen activator (uPA) is a widely studied anticancer drug target with multiple classes of inhibitors reported to date. Many of these inhibitors contain amidine or guanidine groups, while others lacking these groups show improved oral bioavailability. Most of the X-ray co-crystal structures of small molecule uPA inhibitors show a key salt bridge with the side chain carboxylate of Asp189 in the S1 pocket of uPA. This review summarises the different classes of uPA inhibitors, their binding interactions and experimentally measured inhibitory potencies and highlights species selectivity issues with attention to recently described 6-substituted amiloride and 5‑N,N-(hexamethylene)amiloride (HMA) derivatives.

Highly Efficient and Ambient-Temperature Synthesis of Benzimidazoles via Co(III)/Co(II)-Mediated Redox Catalysis

An efficient method for ambient-temperature synthesis of a variety of 2-substituted and 1,2-disubstituted benzimidazoles from aldehyde and phenylenediamine substrates has been developed by utilizing Co(III)/Co(II)-mediated redox catalysis. The combination of only 1 mol% of Co(acac)2 and stoichiometric amount of hydrogen peroxide provides a fast, green, and mild access to a diversity of benzimidazoles under solvent-free conditions.

Metal-Free C-H/C-H Coupling of 2H-Imidazole 1-Oxides with Polyphenols toward Imidazole-Linked Polyphenolic Compounds

The methodology of nucleophilic substitution of hydrogen (S_N^H) was successfully applied as a convenient synthetic tool to afford azaheterocyclic derivatives of phenols of various architectures. A series of 26 novel imidazole-linked polyphenolic compounds were first prepared in 72-95% yields through the direct metal-free C-H/C-H coupling of polyphenols with 2H-imidazole 1-oxides. Comprehensive studies on the reaction condition optimization, scope, and limitations enabled the development of a straightforward method toward novel bifunctional derivatives bearing both phenolic and imidazole scaffolds of particular interest in the design of challenging molecules for versatile applications in medicinal chemistry and materials science.

Modifications at C(5) of 2-(2-Pyrrolidinyl)-Substituted 1,4-Benzodioxane Elicit Potent α4β2 Nicotinic Acetylcholine Receptor Partial Agonism with High Selectivity over the α3β4 Subtype

A series of diastereomeric 2-(2-pyrrolidinyl)-1,4-benzodioxanes bearing a small, hydrogen-bonding substituent at the 7-, 6-, or 5-position of benzodioxane have been studied for α4β2 and α3β4 nicotinic acetylcholine receptor affinity and activity. Analogous to C(5)H replacement with N and to a much greater extent than decoration at C(7), substitution at benzodioxane C(5) confers very high α4β2/α3β4 selectivity to the α4β2 partial agonism. Docking into the two receptor structures recently determined by cryo-electron microscopy and site-directed mutagenesis at the minus β2 side converge in indicating that the limited accommodation capacity of the β2 pocket, compared to that of the β4 pocket, makes substitution at C(5) rather than at more projecting C(7) position determinant for this pursued subtype selectivity.

New Benzimidazole-1,2,4-Triazole Hybrid Compounds: Synthesis, Anticandidal Activity and Cytotoxicity Evaluation

Owing to the growing need for antifungal agents, we synthesized a new series 2-((5-(4-(5-substituted-1H-benzimidazol-2-yl)phenyl)-4-substituted-4H-1,2,4-triazol-3-yl)thio)-1-(substitutedphenyl)ethan-1-one derivatives, which were tested against Candida species. The synthesized compounds were characterized and elucidated by FT-IR, ¹H-NMR, ¹³C-NMR and HR-MS spectroscopies. The synthesized compounds were screened in vitro anticandidal activity against Candida species by broth microdiluation methods. In vitro cytotoxic effects of the final compounds were determined by MTT assay. Microbiological studies revealed that compounds 5m, 5o, 5r, 5t, 5y, 5ab, and 5ad possess a good antifungal profile. Compounds 5w was the most active derivative and showed comparable antifungal activity to those of reference drugs ketoconazole and fluconazole. Cytotoxicity evaluation of compounds 5m, 5o, 5r, 5w, 5y, 5ab and 5ad showed that compounds 5w and 5ad were the least cytotoxic agents. Effects of these two compounds against ergosterol biosynthesis were observed by LC-MS-MS method, which is based on quantification of ergosterol level in C. albicans. Compounds 5w and 5d inhibited ergosterol biosynthesis concentration dependently. A fluorescence microscopy study was performed to visualize effect of compound 5w against C. albicans at cellular level. It was determined that compound 5w has a membrane damaging effect, which may be related with inhibition of biosynthesis of ergosterol.

Structure-activity relationship studies for multitarget antithrombotic drugs

Thrombosis is a complex process involving multiple pathways. Currently, therapy relies on the combination of two or more antithrombotic drugs, showing that inhibiting more than one target provides benefits in the prevention and treatment of thrombosis. This review focuses on structure-activity relationship studies of molecules possessing multiple actions against thrombosis, namely, dual inhibitors of coagulation, dual inhibitors of coagulation and platelet aggregation, and also dual inhibitors of platelet aggregation. EP217609 has just entered clinical trials, which raise the expectations on the multitarget strategy to prevent or treat thrombosis.

Hydrogen Bonding of 1,2-Azaborines in the Binding Cavity of T4 Lysozyme Mutants: Structures and Thermodynamics

Protein crystallography and calorimetry were used to characterize the binding of 1,2-azaborines to model cavities in T4 lysozyme in direct comparison to their carbonaceous counterparts. In the apolar L99A cavity, affinity for Ab dropped only slightly versus benzene. In the cavity designed to accommodate a single hydrogen bond (L99A/M102Q), Gln102═O···H-N hydrogen bonding for Ab and BEtAb was observed in the crystallographic complexes. The strength of the hydrogen bonding was estimated as 0.94 and 0.64 kcal/mol for Ab and BEtAb, respectively. This work unambiguously demonstrates that 1,2-azaborines can be readily accommodated in classic aryl recognition pockets and establishes one of 1,2-azaborine's distinguishing features from its carbonaceous isostere benzene: its ability to serve as an NH hydrogen bond donor in a biological setting.

Selective and Efficient Generation of ortho-Brominated para-Substituted Phenols in ACS-Grade Methanol

The mono ortho-bromination of phenolic building blocks by NBS has been achieved in short reaction times (15-20 min) using ACS-grade methanol as a solvent. The reactions can be conducted on phenol, naphthol and biphenol substrates, giving yields of >86% on gram scale. Excellent selectivity for the desired mono ortho-brominated products is achieved in the presence of 10 mol % para-TsOH, and the reaction is shown to be tolerant of a range of substituents, including CH3, F, and NHBoc.

Expedient synthesis of benzimidazoles using amides

In the present report an efficient, rapid, facile and inexpensive route for the synthesis of benzimidazoles using 1,2-arylenediamines and amides in acidic medium under thermal/microwave conditions is developed.

Eco-Friendly Synthesis of 2-Substituted Benzimidazoles Using Air as the Oxidant

A simple, environmentally friendly procedure for the synthesis of 2-substituted benzimidazoles by the one-pot condensation of o-phenylenediamines with aromatic aldehydes using continuous bubbling of air in absolute ethanol at room temperature is described. The simplicity of the system, mild conditions, involvement of a non-toxic and practically inexhaustible oxidant, easy and quick isolation of the products, and moderate to good yields are the main advantages of this procedure.

Synthesis of novel 1,2,5-trisubstituted benzimidazoles as potential antitumor agents

Novel methyl 1-(5-tert-butyl-1H-pyrazol-3-yl)-2-(aryl)-1H-benzo[d]imidazole-5-carboxylates 11 were synthesized by following a four-step strategy involving a nucleophilic aromatic displacement (S(N)Ar) and a solvent free approach as key steps for the formation of the desired products. Structure of intermediates and products were confirmed by X-ray diffraction as well as the tautomeric rearrangement suffered by the pyrazole moiety during the curse of the final cyclization process. Several of the obtained compounds were screened by the US National Cancer Institute (NCI) for their ability to inhibit 60 different human tumor cell lines. Products 11b and 11n exhibited the highest activity against a range of cancer cell lines with remarkable values in panels of Non-Small Cell Lung Cancer, Melanoma and Leukemia, with GI(50) range of 1.15-7.33 μM and 0.167-7.59 μM, respectively, and suitable LC(50) with values greater than 100 μM.