α2-Adrenoceptor Antagonists: Synthesis, Pharmacological Evaluation, and Molecular Modeling Investigation of Pyridinoguanidine, Pyridino-2-aminoimidazoline and Their Derivatives

Antibacterial activity of isopropoxy benzene guanidine against Riemerella anatipestifer

Introduction: Riemerella anatipestifer (R. anatipestifer) is an important pathogen in waterfowl, leading to substantial economic losses. In recent years, there has been a notable escalation in the drug resistance rate of R. anatipestifer. Consequently, there is an imperative need to expedite the development of novel antibacterial medications to effectively manage the infection caused by R. anatipestifer. Methods: This study investigated the in vitro and in vivo antibacterial activities of a novel substituted benzene guanidine analog, namely, isopropoxy benzene guanidine (IBG), against R. anatipestifer by using the microdilution method, time-killing curve, and a pericarditis model. The possible mechanisms of these activities were explored. Results and Discussion: The minimal inhibitory concentration (MIC) range of IBG for R. anatipestifer was 0.5-2 μg/mL. Time-killing curves showed a concentration-dependent antibacterial effect. IBG alone or in combination with gentamicin significantly reduced the bacterial load of R. anatipestifer in the pericarditis model. Serial-passage mutagenicity assays showed a low probability for developing IBG resistance. Mechanistic studies suggested that IBG induced membrane damage by binding to phosphatidylglycerol and cardiolipin, leading to an imbalance in membrane potential and the transmembrane proton gradient, as well as the decreased of intracellular adenosine triphosphate. In summary, IBG is a potential antibacterial for controlling R. anatipestifer infections.

Effects of sidechain isomerism on polymer-based non-covalent protein delivery

We present the importance of functional group isomerism on intracellular protein delivery using polymers containing different isomeric side chains. While the physical properties of polymer/protein complexes are relatively similar, different planarity of the isomers greatly influences the cellular entry efficiency.

Hexadentate technetium-99m bis(thiosemicarbazonato) complexes: synthesis, characterisation and biodistribution

The syntheses of non-oxido/non-nitrido bis(thiosemicarbazonato)technetium(V) complexes featuring a series of alkyl and ether substituents is presented. The bis(thiosemicarbazones) were radiolabelled with technetium-99m using an optimised one-pot synthesis from [^99mTc][TcO₄]^-. Mass spectrometry and computational chemistry data suggested a distorted trigonal prismatic coordination environment for the bis(thiosemicarbazonato)technetium(V) complexes by way of a bis(thiosemicarbazone)technetium(V)-oxido intermediate complex. The lipophilicities of the complexes were estimated using distribution ratios and three of the new complexes were investigated in mice using kinetic planar imaging and ex vivo biodistribution experiments and were compared to [^99mTc][TcO₄]^-. Modification of the technetium complexes with various lipophilic functional groups altered the biodistributions of the complexes in mice despite evidence suggesting limited stability of the complexes to biologically relevant conditions. The most hydrophilic complex had higher uptake in the kidneys compared to the most lipophilic, which had higher liver uptake, suggesting modification of the excretion pathways.

Regioselective Access to 2-Iminoimidazolidines via AgF-Mediated Cascade Reactions

A convergent access to substituted 2-iminoimidazolidines from aromatic amines and N-propargyl S-methylthiourea is developed via Ag(I)-mediated cascade guanylation-cyclization reactions. This method features high regioselectivity, excellent efficiency, and mild reaction conditions. Subsequent deprotection of the Boc (tert-butyloxycarbonyl) group under acidic conditions provides expedient access to aryl 2-aminoimidazole derivatives in a convenient manner.

1,3-Diazepine: A privileged scaffold in medicinal chemistry

Privileged structures have been widely used as effective templates for drug discovery. While benzo-1,4-diazepine constitutes the first historical example of such a structure, the 1,3 analogue is just as rich in terms of applications in medicinal chemistry. The 1,3-diazepine moiety is present in numerous biological active compounds including natural products, and is used to design compounds displaying a large range of biological activities. It is present in the clinically used anticancer compound pentostatin, in several recent FDA approved β-lactamase inhibitors (e.g., avibactam) and also in coformycin, a natural product known as a ring-expanded purine analogue displaying antiviral and anticancer activities. Several other 1,3-diazepine containing compounds have entered into clinical trials. This heterocyclic structure has been and is still widely used in medicinal chemistry to design enzyme inhibitors, GPCR ligands, and so forth. This review endeavours to highlight the main use of the 1,3-diazepine scaffold and its derivatives, and their applications in medicinal chemistry, drug design, and therapy. We will focus more particularly on the development of enzyme inhibitors incorporating this scaffold, with a strong emphasis on the molecular interactions involved in the inhibition mechanism.

Di-aryl guanidinium derivatives: Towards improved α2-Adrenergic affinity and antagonist activity

Compounds with excellent receptor engagement displaying α₂-AR antagonist activity are useful not only for therapeutic purposes (e.g. antidepressants), but also to help in the crystallization of this particular GPCR. Therefore, based on our broad experience in the topic, we have prepared eighteen di-aryl (phenyl and/or pyridin-2-yl) mono- or di-substituted guanidines and 2-aminoimidazolines. The in vitro α₂-AR binding affinity experiments in human brain tissue showed the advantage of a 2-aminoimidazolinium cation, a di-arylmethylene core, a conformationally locked pyridin-2-yl-guanidine and a di-substituted guanidinium to achieve good α₂-AR engagement. After different in vitro [³⁵S]GTPγS binding experiments in human prefrontal cortex tissue, it was possible to identify that compounds 7a, 7b and 7c were α₂-AR partial agonist, whereas 8h was a potent α₂-AR antagonist. Docking and MD studies with a model of α_2A-AR and two crystal structures suggest that antagonism is achieved by compounds carrying a di-substituted guanidine which substituent occupy a pocket adjacent to TM5 without engaging S200^5.42 or S204^5.46, and a mono-substituted cationic group, which favorably interacts with E94^2.65.

Divergent 2-Chloroquinazolin-4(3H)-one Rearrangement: Twisted-Cyclic Guanidine Formation or Ring-Fused N-Acylguanidines via a Domino Process

A highly efficient 2-chloroquinazolin-4(3H)-one rearrangement was developed that predictably generates either twisted-cyclic or ring-fused guanidines in a single operation, depending on the presence of a primary versus secondary amine in the accompanying diamine reagent. Exclusive formation of twisted-cyclic guanidines results from pairing 2-chloroquinazolinones with secondary diamines. Use of primary amine-containing diamines permits a domino quinazolinone rearrangement/intramolecular cyclization, gated through (E)-twisted-cyclic guanidines, to afford ring-fused N-acylguanidines. This scalable, structurally tolerant transformation generated 55 guanidines and delivered twisted-cyclic guanidines with robust plasma stability and an abbreviated total synthesis of an antitumor ring-fused guanidine (4 steps, 55 % yield).

Singlet oxygen mediated dual C–C and C–N bond cleavage in visible light

A tandem cleavage of carbon–carbon and carbon–nitrogen bonds in imidazo[1,2-a]pyridines and imidazo[1,2-a]quinolines is reported in the presence of eosin Y and visible light.

A highly enantioselective synthetic method towards the α2c-adrenoceptor antagonist ORM-10921

The preparation of ORM-10921, a selective α_2C-adrenoceptor antagonist with promising anti-psychotic properties, was successfully achieved using asymmetric α-alkylation of α,β-unsaturated imide and Bischler–Napieralski cyclization/asymmetric reduction as the key steps.

Prediction of Aqueous pK a Values for Guanidine-Containing Compounds Using Ab Initio Gas-Phase Equilibrium Bond Lengths

In this work, we demonstrate the existence of linear relationships between gas-phase equilibrium bond lengths of the guanidine skeleton of 2-(arylamino)imidazolines and their aqueous pK _a value. For a training set of 22 compounds, in the most stable conformation of their lowest energy tautomeric form, three bonds were found to exhibit r ² and q ² values >0.95 and root-mean-squared-error of estimation values ≤0.25 when regressed individually against pK _a. The equations describing these one-bond-length linear relationships, in addition to a multiple linear regression model using all three bond lengths, were then used to predict the experimental pK _a values of an external test set of further 27 derivatives. The optimal protocol we derive here shows an overall mean absolute error (MAE) of 0.20 and standard deviation of errors of 0.18 for the test set. Predictions for a second test set of diphenyl-based bis(2-iminoimidazolidines) yielded an MAE of 0.27 and a standard deviation of 0.10. The predictive power of the optimal model is further demonstrated by its ability to correct erroneously reported experimental values. Finally, a previously established guanidine model is recalibrated at a new level of theory, and predictions are made for novel phenylguanidine derivatives, showing an MAE of just 0.29. The protocols established and tested here pass both of Roy's modern and stringent MAE-based criteria for a "good" quantitative structure-activity relationship/quantitative structure-property relationship model predictivity. Notably, the ab initio bond length high correlation subset protocol developed in this work demonstrates lower MAE values than the Marvin program by ChemAxon for all test sets.

Phenylpyridine-2-ylguanidines and rigid mimetics as novel inhibitors of TNFα overproduction: Beneficial action in models of neuropathic pain and of acute lung inflammation

4-phenylpyridin-2-yl-guanidine (5b): a new inhibitor of the overproduction of pro-inflammatory cytokines (TNFα and Il1β) was identified from a high-throughput screening of a chemical library on human peripheral blood mononuclear cells (PBMCs) after LPS stimulation. Derivatives, homologues and rigid mimetics of 5b were designed and synthesized, and their cytotoxicity and ability to inhibit TNFα overproduction were evaluated. Among them, compound 5b and its mimetic 12 (2-aminodihydroquinazoline) showed similar inhibitory activities, and were evaluated in vivo in models of lung inflammation and neuropathic pain in mice. In particular, compound 12 proved to be active (5 mg/kg, ip) in both models.

Substituent effects on the basicity (pKa) of aryl guanidines and 2-(arylimino)imidazolidines: correlations of pH-metric and UV-metric values with predictions from gas-phase ab initio bond lengths

The AIBLHiCoS method accurately predicts the pK_a values of 2-(arylimino)imidazolidines using only a single ab initio bond length.

The chemistry and biology of guanidine natural products

The chemistry and biology of natural guanidines isolated from microbial culture media, from marine invertebrates, as well as from terrestrial plants and animals, are reviewed.

Aromatic Amino Acids-Guanidinium Complexes through Cation-π Interactions

Continuing with our interest in the guanidinium group and the different interactions than can establish, we have carried out a theoretical study of the complexes formed by this cation and the aromatic amino acids (phenylalanine, histidine, tryptophan and tyrosine) using DFT methods and PCM-water solvation. Both hydrogen bonds and cation-π interactions have been found upon complexation. These interactions have been characterized by means of the analysis of the molecular electron density using the Atoms-in-Molecules approach as well as the orbital interactions using the Natural Bond Orbital methodology. Finally, the effect that the cation-π and hydrogen bond interactions exert on the aromaticity of the corresponding amino acids has been evaluated by calculating the theoretical NICS values, finding that the aromatic character was not heavily modified upon complexation.

Rh(iii)-catalyzed [5+1] oxidative cycloaddition of arylguanidines with alkynes: a novel access to C4-disubstituted 1,4-dihydroquinazolin-2-amines

A novel and mild Rh^III-catalyzed [5+1] oxidative cycloaddition between arylguanidines and alkynes efficiently affords C4-disubstituted 1,4-dihydroquinazolin-2-amines.