Biological activities of guanidine compounds, 2008 - 2012 update

Zebrafish as a model for assessing biocide toxicity: A comprehensive review

The utilization of biocides in a myriad of products has become a widespread and critical practice in recent years. Among these, quaternary ammonium compounds, polyhexamethylene, parabens, and triclosan are notably prevalent across various industrial applications. However, the incorporation of these biocides raises significant concerns regarding their toxicological profile. Not only do these chemicals pose potential risks to consumers using biocide-containing products, but their environmental discharge also represents a substantial threat to the biosphere. In our meticulous review, we examined approximately 150 articles from esteemed databases including PubMed, MDPI, and Google Scholar, ultimately utilizing at least 88 of these articles to inform our analysis. Our investigation encompassed studies that probe general toxicity, behavioral toxicity, cardiovascular toxicity, and genotoxicity, among other toxicological impacts. With this comprehensive approach, we explore the zebrafish (Danio rerio) as a prominent model organism in toxicology research. This review article aims to synthesize research employing zebrafish to evaluate biocide toxicity and ascertain the suitability of this model for comprehensive analysis of biocidal agents and their associated products.

Unfolding the Potential of Pyrrole- and Indole-Based Allylidene Hydrazine Carboximidamides as Antimicrobial Agents

Antimicrobial drug resistance is a significant global health challenge, causing hundreds of thousands of deaths annually and severely impacting healthcare systems worldwide. Several reported antimicrobial compounds have a guanidine motif, as the positive charge on guanidine promotes cell lysis. Therefore, pyrrole- and indole-based allylidene hydrazine carboximidamide derivatives with guanidine motifs are proposed as antimicrobial agents that mimic cationic antimicrobial peptides (CAMPs). A total of 72 derivatives having pyrrol-2-yl-phenyl allylidene hydrazine carboximidamide and indol-3-yl-phenyl allylidene hydrazine carboximidamide scaffolds were assessed for their inhibitory potential against a panel of Gram-positive and Gram-negative bacteria. Analogs 1j, 1k, 1s, 2j, 2q, 4a, 4c, 4h, 5b, 6a, and 6d exhibited potent broad-spectrum antimicrobial activity better than the standard antibiotics. Also, these compounds showed no cytotoxicity up to 3-fold of the minimum inhibitory concentration, and structure-activity relationship was established. Further, the most active compound, 6a, showed a strong biofilm disruption, acted on the bacterial membrane, and lysed it. The further development of these compounds as novel antimicrobial agents is warranted.

Antifungal activity of guanidine compounds

Guanidinic compounds are a class of compounds distributed in nature but also synthesized in vitro with a wide variety of applicability. One of the potentials of those molecules is antimicrobial activity. In that sense, although mainly limited to immunocompromised people, fungi pathogens are a cause of concern, even more so after the COVID-19 pandemic. Susceptible groups and increased geographical distribution, besides drug toxicity, resistance, and high costs, made the World Health Organization (WHO) establish a guideline for research and public health politics against different fungi opportunist agents. Our present work evaluated the antifungal activity of 11 guanidine compounds (one of them synthesized for the first time) against six fungi species in the WHO Fungi Priority Pathogens List and their potential for antimicrobial selectivity. The newly synthesized compound, named LQOF-G2-S, was successfully obtained and chemically characterized as spermidine tri-substituted by guanidine moieties in benzylamine-4-bromoaniline groups, and it presented the best antifungal activity and selectivity among the others. It was the only compound active against Candida spp.; however, its activity was more promising against Cryptococcus neoformans, Cryptococcus gattii, and even more against Paracoccidioides brasiliensis and Paracoccidioides lutzii, with a selective index higher than 10. The LQOF-G2-S potential opened up the opportunity to design and evaluate other similar compounds, contributing to finding new effective, less toxic, and more affordable compounds for fungi treatment.

2-Guanidinobenzimidazole as Ligand in Supramolecular, Coordination and Organometallic Chemistry

The benzimidazole core (BI) plays a central role in biologically active molecules. The BI nucleus is widely used as a building block to generate a variety of bioactive heterocyclic compounds to be used as antihelmintics, antiprotozoal, antimalarials, anti-inflammatories, antivirals, antimicrobials, antiparasitics, and antimycobacterials. A versatile BI derivative is the 2-guanidinobenzimidazole (2GBI), which, together with its derivatives, is a very interesting poly-functional planar molecule having a delocalised 10 π electrons system conjugated with the guanidine group. The 2GBI molecule has five nitrogen atoms containing five labile N-H bonds, which interact with the out-ward-facing channel entrance, forming a labile complex with the biological receptor sites. In this work, 2GBI and their derivatives were analyzed as ligands to form host-guest, coordination and organometallic complexes. Synthesis methodology, metal geometries, hydrogen bonding (HB) interactions, and the biological activities of the complexes were discussed.

Advances in Cysteine Protease B Inhibitors for Leishmaniasis Treatment

The expression and release of cysteine proteases by Leishmania spp. and their virulence factors significantly influence the modulation of host immune responses and metabolism, rendering cysteine proteases intriguing targets for drug development. This review article explores the substantial role of cysteine protease B (CPB) in medicinal chemistry from 2001 to 2024, particularly concerning combatting Leishmania parasites. We delve into contemporary advancements and potential prospects associated with targeting cysteine proteases for therapeutic interventions against leishmaniasis, emphasizing drug discovery in this context. Computational analysis using the pkCSM tool assessed the physicochemical properties of compounds, providing valuable insights into their molecular characteristics and drug-like potential, enriching our understanding of the pharmacological profiles, and aiding rational inhibitor design. Our investigation highlights that while nonpeptidic compounds constitute the majority (69.2%, 36 compounds) of the dataset, peptidomimetic- based derivatives (30.8%, 16 compounds) also hold promise in medicinal chemistry. Evaluating the most promising compounds based on dissociation constant (Ki) and half maximal inhibitory concentration (IC50) values revealed notable potency, with 41.7% and 80.0% of nonpeptidic compounds exhibiting values < 1 μM, respectively. On the other hand, all peptidic compounds evaluated for Ki (43.8%) and IC50 (31.3%) obtained values < 1 μM, respectively. Further analysis identified specific compounds within both categories (nonpeptidic: 1, 2, and 4; peptidic: 48-52) as particularly promising, warranting deeper investigation into their structure-activity relationships. These findings underscore the diverse landscape of inhibitors in medicinal chemistry and highlight the potential of both nonpeptidic and peptide-based compounds as valuable assets in therapeutic development against leishmaniasis.

Guanidine dicycloamine-based analogs: green chemistry synthesis, biological investigation, and molecular docking studies as promising antibacterial and antiglycation leads

Dicyandiamide (DCD) reacted with amino acids 1a-f to produce biguanides 2 and 4 and guanidine pyrazolones 3, 5, 6, 7, and 8, according to the reaction. DCD exhibited the following reactions: imidodicarbonimidicdiamide 9, diazocan-2-ylguanidine 10, methyl biguanidylthion 11, N-carbamothioylimidodicarbonimidicdiamide 12, 2-guanidinebenzoimidazole 13a, 2-guanidinylbenzoxazole 13b, and 2-guanidinylbenzothiazol 13c. These reactions were triggered by 6-amino caproic acid, thioacetamide, thiourea, o-aminophenol, o-aminothiophenol, and anthranilic acid, respectively. Compound 2 had the least antimicrobial activity, while compound 13c demonstrated the most antibacterial impact against all bacterial strains. Furthermore, in terms of antiglycation efficacy (AGEs), 12, 11, and 7 were the most effective AGE cross-linking inhibitors. Eight and ten, which showed a considerable inhibition on cross-linking AGEs, come next. Compounds 4 and 6 on the other hand have shown the least suppression of AGE production. The most promising antiglycation scaffolds 8, 11, and 12 in the Human serum albumin (HAS) active site were shown to be able to adopt crucial binding interactions with important amino acids based on the results of in silico molecular docking. The most promising antiglycation compounds 8, 11, and 12 were also shown to have better hydrophilicity, acceptable lipophilicity, gastrointestinal tract absorption (GIT), and blood-brain barrier penetration qualities when their physicochemical properties were examined using the egg-boiled method.

Development of Novel Membrane Disrupting Lipoguanidine Compounds Sensitizing Gram-Negative Bacteria to Antibiotics

A new class of amphiphilic molecules, the lipoguanidines, designed as hybrids of guanidine and fatty acid compounds, has been synthesized and developed. The new molecules present both a guanidine polar head and a lipophilic tail that allow them to disrupt bacterial membranes and to sensitize Gram-negative bacteria to the action of the narrow-spectrum antibiotics rifampicin and novobiocin. The lipoguanidine 5g sensitizes Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli to rifampicin, thereby reducing the antibiotic minimum inhibitory concentrations (MIC) up to 256-fold. Similarly, 5g is able to potentiate novobiocin up to 64-fold, thereby showing a broad spectrum of antibiotic potentiating activity. Toxicity and mechanism studies revealed the potential of 5g to work synergistically with rifampicin through the disruption of bacterial membranes without affecting eukaryotic cells.

Controlled Modification of Triaminoguanidine-Based μ3 Ligands in Multinuclear [VIVO]/[VVO2] Complexes and Their Catalytic Potential in the Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes

Reaction of tris(2-hydroxybenzylidene)-triaminoguanidinium chloride (I·HCl) and tris(5-bromo-2-hydroxybenzylidene)-triaminoguanidinium chloride (II·HCl) with [VIVO(acac)2] (1:1 molar ratio) in refluxing methanol resulted in mononuclear [VIVO] complexes, [VIVO(H2L1')(MeOH)] (1) and [VIVO(H2L2')(MeOH)] (2), respectively, where I and II undergo intramolecular triazole ring formation. Aerial oxidation of 1 and 2 in MeOH in the presence of Cs2CO3 gave corresponding cis-[VVO2] complexes Cs[(VO2)(H2L1')] (3) and Cs[(VO2)(H2L2')] (4). However, reaction of an aerially oxidized methanolic solution of [VIVO(acac)2] with I·HCl and II·HCl in the presence of Cs2CO3 (in 1:1:1 molar ratio) gave mononuclear complexes Cs[(VO2)(H3L1)] (5) and Cs[(VO2)(H3L2)] (6) without intramolecular triazole ring formation. Similar anionic trinuclear complexes Cs2[(VO2)3(L1)] (7) and Cs2[(VO2)3(L2)] (8) were isolable upon increasing the amounts of the vanadium precursor and Cs2CO3 to 3 equiv to the reaction applied for 5 and 6. Keeping the reaction mixture of 1 in MeOH under air gave [VVO(H2L1')(OMe)] (9). Structures of 3, 7, 8, and 9 were confirmed by X-ray crystal structure study. A permanent porosity in the crystalline metal-organic framework of 7 confirmed by single-crystal X-ray investigation was further verified by the BET study. Along with a suitable reaction mechanism, these synthesized compounds were explored as effective catalysts for the synthesis of biomolecules 4H-pyran/4H-chromenes.

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.

Synthetic and natural guanidine derivatives as antitumor and antimicrobial agents: A review

Guanidines are fascinating small nitrogen-rich organic compounds, which have been frequently associated with a wide range of biological activities. This is mainly due to their interesting chemical features. For these reasons, for the past decades, researchers have been synthesizing and evaluating guanidine derivatives. In fact, there are currently on the market several guanidine-bearing drugs. Given the broad panoply of pharmacological activities displayed by guanidine compounds, in this review, we chose to focus on antitumor, antibacterial, antiviral, antifungal, and antiprotozoal activities presented by several natural and synthetic guanidine derivatives, which are undergoing preclinical and clinical studies from January 2010 to January 2023. Moreover, we also present guanidine-containing drugs currently in the market for the treatment of cancer and several infectious diseases. In the preclinical and clinical setting, most of the synthesized and natural guanidine derivatives are being evaluated as antitumor and antibacterial agents. Even though DNA is the most known target of this type of compounds, their cytotoxicity also involves several other different mechanisms, such as interference with bacterial cell membranes, reactive oxygen species (ROS) formation, mitochondrial-mediated apoptosis, mediated-Rac1 inhibition, among others. As for the compounds already used as pharmacological drugs, their main application is in the treatment of different types of cancer, such as breast, lung, prostate, and leukemia. Guanidine-containing drugs are also being used for the treatment of bacterial, antiprotozoal, antiviral infections and, recently, have been proposed for the treatment of COVID-19. To conclude, the guanidine group is a privileged scaffold in drug design. Its remarkable cytotoxic activities, especially in the field of oncology, still make it suitable for a deeper investigation to afford more efficient and target-specific drugs.

Stability of DNA Origami Nanostructures in Physiological Media: The Role of Molecular Interactions

Programmable, custom-shaped, and nanometer-precise DNA origami nanostructures have rapidly emerged as prospective and versatile tools in bionanotechnology and biomedicine. Despite tremendous progress in their utilization in these fields, essential questions related to their structural stability under physiological conditions remain unanswered. Here, DNA origami stability is explored by strictly focusing on distinct molecular-level interactions. In this regard, the fundamental stabilizing and destabilizing ionic interactions as well as interactions involving various enzymes and other proteins are discussed, and their role in maintaining, modulating, or decreasing the structural integrity and colloidal stability of DNA origami nanostructures is summarized. Additionally, specific issues demanding further investigation are identified. This review - through its specific viewpoint - may serve as a primer for designing new, stable DNA objects and for adapting their use in applications dealing with physiological media.

Isopropoxy Benzene Guanidine Ameliorates Streptococcus suis Infection In Vivo and In Vitro

Streptococcus suis, an encapsulated zoonotic pathogen, has been reported to cause a variety of infectious diseases, such as meningitis and streptococcal-toxic-shock-like syndrome. Increasing antimicrobial resistance has triggered the need for new treatments. In the present study, we found that isopropoxy benzene guanidine (IBG) significantly attenuated the effects caused by S. suis infection, in vivo and in vitro, by killing S. suis and reducing S. suis pathogenicity. Further studies showed that IBG disrupted the integrity of S. suis cell membranes and increased the permeability of S. suis cell membranes, leading to an imbalance in proton motive force and the accumulation of intracellular ATP. Meanwhile, IBG antagonized the hemolysis activity of suilysin and decreased the expression of Sly gene. In vivo, IBG improved the viability of S. suis SS3-infected mice by reducing tissue bacterial load. In conclusion, IBG is a promising compound for the treatment of S. suis infections, given its antibacterial and anti-hemolysis activity.

New ferrocene integrated amphiphilic guanidines: Synthesis, spectroscopic elucidation, DFT calculation and in vitro α-amylase and α-glucosidase inhibition combined with molecular docking approach

Three N, N', N″-trisubstituted ferrocenyl guanidines (MG-10, MG-12 and MG-14) were synthesized, characterized by several analytical methods such as FT-IR, ¹H and ¹³C NMR, elemental analysis and UV-visible spectroscopy. These compounds have long chain aliphatic groups therefore their aliphatic nature has been evaluated by determining their critical micelle concentration (CMC). CMC point decreases from 0.036 mM to 0.013 mM with increase in the aliphatic chain length. The quantum mechanical parameters such as the energy of frontier molecular orbitals (E_HOMO and E_LUMO) and the Mulliken charge distribution on the optimized structures were determined using a DFT/B3LYP method combined with the 6-31G (d,p) basis set in the gas phase. The in vitro antidiabetic activity of synthesized compounds showed that MG-12 has IC₅₀value 23.10 μg/mL against α-amylase while MG-10 has IC₅₀value 27.32 μg/mL against α-glucosidase with the respective standard Acarbose (IC₅₀value 20.12 μg/mL). Theoretical docking analysis demonstrated that MG-10 and MG-12 interacted with α-amylase by 3 types of interaction, including hydrogen bonds, hydrophobic interactions and electrostatic interactions.

LQM10, a guanylhydrazone derivative, reduces nociceptive and inflammatory responses in mice

In the present study, we examined the antinociceptive and anti-inflammatory activities of a guanylhydrazone derivative, (E)-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2-guanylhydrazone hydrochloride (LQM10), in mice. The antinociceptive effect was determined by assessing behavioural responses in different pain models, while anti-inflammatory activity was examined in carrageenan-induced pleurisy. Intraperitoneal LQM10 administration reduced the acetic acid-induced nociceptive behaviour, a phenomenon that was unaltered by pretreatment with yohimbine, atropine, naloxone or glibenclamide. In the formalin assay, LQM10 reduced nociceptive behaviour only in the second phase, indicating an inhibitory effect on inflammatory pain. LQM10 did not alter the pain latency in the hot plate assay and did not impact the locomotor activity of mice in the rotarod assay. In the carrageenan-induced pleurisy assay, LQM10 treatment inhibited critical events involved in inflammatory responses, namely, leucocyte recruitment, plasma leakage and increased inflammatory mediators (tumour necrosis factor Like Properties of Chalchones and Flavonoid Derivatives [TNF]-α and interleukin [IL]-1β) in the pleural exudate. Overall, these results indicate that LQM10 exhibits antinociceptive effects associated with peripheral mechanisms and anti-inflammatory activity mediated via a reduction in leucocyte migration and proinflammatory mediators, rendering this compound a promising candidate for treating pain and inflammatory process.

Enhancement of the oral bioavailability of isopropoxy benzene guanidine though complexation with hydroxypropyl-β-cyclodextrin

Isopropoxy benzene guanidine (IBG) is a novel substituted benzene guanidine analogue with antibacterial activity against multidrug-resistant bacteria. However, the bioavailability of IBG is not optimal due to its finite aqueous solubility, thus hampering its potential therapeutic exploitation. In this study, we prepared IBG/hydroxypropyl-β-CD (IBG/HP-β-CD) complex, and characterized it by differential scanning calorimetry, Fourier transform infrared spectroscopy, powder X-ray diffraction, and scanning electron microscopy. Physicochemical characterization indicated that the crystal morphology of IBG transformed into an amorphous state, thus forming IBG/HP-β-CD inclusion complexes. Complexation with HP-β-CD significantly improve the aqueous solubility, pharmaceutical properties, absorption, and bioavailability of IBG.

Pharmacokinetics and pharmacodynamics of isopropoxy benzene guanidine against Clostridium perfringens in an intestinal infection model

This study aimed to evaluate the antibacterial activity of isopropoxy benzene guanidine (IBG) against C. perfringens based on pharmacokinetics/pharmacodynamics (PK/PD) modeling in broilers. The PK parameters of IBG in the plasma and ileal content of C. perfringens-infected broilers following oral administration at 2, 30, and 60 mg/kg body weight were investigated. in vivo PD studies were conducted over oral administration ranging from 2 to 60 mg/kg and repeated every 12 h for 3 days. The inhibitory I_max model was used for PK/PD modeling. Results showed that the MIC of IBG against C. perfringens was 0.5–32 mg/L. After oral administration of IBG, the peak concentration (C_max), maximum concentration time (T_max), and area under the concentration-time curve (AUC) in ileal content of broilers were 10.97–1,036.64 mg/L, 2.39–4.27 h, and 38.31–4,266.77 mg·h/L, respectively. After integrating the PK and PD data, the AUC_{0 − 24h}/MIC ratios needed for the bacteriostasis, bactericidal activity, and bacterial eradication were 4.00, 240.74, and 476.98 h, respectively. For dosage calculation, a dosage regimen of 12.98 mg/kg repeated every 12 h for 3 days was be therapeutically effective in broilers against C. perfringens with MIC ≤ 2 mg/L. In addition, IBG showed potent activity against C. perfringens, which may be responsible for cell membrane destruction. These results can facilitate the evaluation of the use of IBG in the treatment of intestinal diseases in broilers caused by C. perfringens.

Pharmacokinetics and Pharmacodynamics of Colistin Combined With Isopropoxy Benzene Guanidine Against mcr-1-Positive Salmonella in an Intestinal Infection Model

Plasmid-borne colistin resistance mediated by mcr-1 is a growing problem, which poses a serious challenge to the clinical application of colistin for Gram-negative bacterial infections. Drug combination is one of the effective strategies to treat colistin-resistant bacteria. Here, we found a guanidine compound, namely, isopropoxy benzene guanidine (IBG), which boosted the efficacy of colistin against mcr-1-positive Salmonella. This study aimed to develop a pharmacokinetics/pharmacodynamics (PK/PD) model by combining colistin with IBG against mcr-1-positive Salmonella in an intestinal infection model. Antibiotic susceptibility testing, checkerboard assays and time-kill curves were used to investigate the antibacterial activity of the synergistic activity of the combination. PK studies of colistin in the intestine were determined through oral gavage of single dose of 2, 4, 8, and 16 mg/kg of body weight in broilers with intestinal infection. On the contrary, PD studies were conducted over 24 h based on a single dose ranging from 2 to 16 mg/kg. The inhibitory effect Imax model was used for PK/PD modeling. The combination of colistin and IBG showed significant synergistic activity. The AUC0−24h/MIC index was used to evaluate the relationship between PK and PD, and the correlation was &gt;0.9085. The AUC0−24h /MIC targets in combination required to achieve the bacteriostatic action, 3-log10 kill, and 4-log10 kill of bacterial counts were 47.55, 865.87, and 1894.39, respectively. These results can facilitate the evaluation of the use of IBG as a potential colistin adjuvant in the treatment of intestinal diseases in broilers caused by colistin-resistant Salmonella.

Synthesis and multifaceted pharmacological activity of novel quinazoline NHE-1 inhibitors

The Na⁺/H⁺ exchanger isoform 1 (NHE-1) attracts ongoing attention as a validated drug target for the management of cardiovascular and ocular diseases owing to cytoprotective, anti-ischemic and anti-inflammatory properties of NHE-1 inhibitors. Herein we report novel NHE-1 inhibitors realized via functionalization of N¹-alkyl quinazoline-2,4(1H,3H)-dione and quinazoline-4(3H)-one with N-acylguanidine or 3-acyl(5-amino-1,2,4-triazole) side chain. Lead compounds show activity in a nanomolar range. Their pharmacophoric features were elucidated with neural network modeling. Several compounds combine NHE-1 inhibition with antiplatelet activity. Compound 6b reduces intraocular pressure in rats and effectively inhibits the formation of glycated proteins. Compounds 3e and 3i inhibit pro-inflammatory activation of murine macrophages, LPS-induced interleukin-6 secretion and also exhibit antidepressant activity similar to amiloride. Hence, novel compounds represent an interesting starting point for the development of agents against cardiovascular diseases, thrombotic events, excessive inflammation, long-term diabetic complications and glaucoma.

Evaluation of 1H-Triazole-1-[N,N'-Bis(tert-butoxycarbonyl)]carboxamidine in Solution-Phase and On-Resin Guanidinylation

Several guanidines and guanidinylated peptides have substantial potential as therapeutics, but efficient guanidinylation reagents are vital for easy access to these compounds. Presently, pyrazole-1-carboxamidine type reagents are commonly used in the transformations of amines into corresponding guanidines. Here, we report a comparative study of the utility of 1H-triazole-1-[N,N'-bis(tert-butoxycarbonyl)]carboxamidine, which was synthesized in two steps and readily upscaled to gram amounts. It exhibited excellent performance in solution-phase reactions, rapidly converting a set of representative aliphatic primary and unhindered secondary amines as well as aniline into the corresponding bis(tert-butoxycarbonyl)-protected guanidines. To enable a direct assessment of the reactivity of guanidinylation reagents, conversions were performed in deuterated solvents (d₇-DMF or d₈-THF), allowing for continuous analysis of the reaction mixtures by ¹H and ¹³C NMR. Likewise, 1H-triazole-1-[N,N'-bis(tert-butoxycarbonyl)]carboxamidine proved to be a versatile reagent in solid-phase conversions, for example, a resin-bound test peptide (KFFKFFK) was fully guanidinylated in only 2 h by using 2 equivalents of the reagent per free amino group. Also, 1H-triazole-1-[N,N'-bis(tert-butoxycarbonyl)]carboxamidine proved capable of completely guanidinylating more sterically hindered N-terminal residues (e.g., N-methyl amino acids or a peptoid) in resin-bound peptides. Its superior reactivity and stability demonstrated under heating conditions make 1H-triazole-1-[N,N'-bis(tert-butoxycarbonyl)]carboxamidine a valuable guanidinylation reagent both in solution- and solid-phase synthesis.

The combined action of cations and anions of ionic liquids modulates the formation and stability of G-quadruplex DNA

G-Quadruplex (Gq) formation and stabilization by any molecule is an essential requirement for its application in therapy, especially in oncology. Metal cations have shown higher propensity of the formation of the Gq structure and its stabilization. In this study, the role of both cations and anions of ionic liquids (ILs) on the Gq formation of human telomere (hTeloG) and its stability was investigated using spectroscopic and molecular dynamics simulation techniques. Irrespective of the nature of anions of ILs, tetramethylguanidinium (TMG) cations associated with different anions can form an antiparallel Gq structure in hTeloG. However, the propensity of the formation of an antiparallel Gq structure and its stability depend on the chain length of anions of ILs. Gq is significantly less stable in ILs having longer hydrocarbon chain anions compared to the short chain anions suggesting that the hydrophobicity of the anion plays a critical role in the stability and formation of the Gq structure by ILs. The data indicate that longer hydrocarbon chain anions of ILs preferably interact in the loop region of Gq through hydrophobic interaction which enhances the overall binding of the cation of ILs with Gq causing a decrease in the stacking energy between the G-quartets as well as Hoogsteen hydrogen bonds between the guanine bases leading to the destabilization of the antiparallel Gq structure.

Structure-Activity Relationship Studies on Oxazolo[3,4-a]pyrazine Derivatives Leading to the Discovery of a Novel Neuropeptide S Receptor Antagonist with Potent In Vivo Activity

Neuropeptide S modulates important neurobiological functions including locomotion, anxiety, and drug abuse through interaction with its G protein-coupled receptor known as neuropeptide S receptor (NPSR). NPSR antagonists are potentially useful for the treatment of substance abuse disorders against which there is an urgent need for new effective therapeutic approaches. Potent NPSR antagonists in vitro have been discovered which, however, require further optimization of their in vivo pharmacological profile. This work describes a new series of NPSR antagonists of the oxazolo[3,4-a]pyrazine class. The guanidine derivative 16 exhibited nanomolar activity in vitro and 5-fold improved potency in vivo compared to SHA-68, a reference pharmacological tool in this field. Compound 16 can be considered a new tool for research studies on the translational potential of the NPSergic system. An in-depth molecular modeling investigation was also performed to gain new insights into the observed structure-activity relationships and provide an updated model of ligand/NPSR interactions.

Antimicrobial drugs bearing guanidine moieties: A review

Compounds incorporating guanidine moieties constitute a versatile class of biologically interesting molecules with a wide array of applications. As such, guanidines have been exploited as privileged structural motifs in designing novel drugs for the treatment of various infectious and non-infectious diseases. In designing anti-infective agents, this moiety carries great appeal by virtue of attributes such as hydrogen-bonding capability and protonatability at physiological pH in the context of interaction with biological targets. This review provides an overview of recent advances in hit-to-lead development studies of antimicrobial guanidine-containing compounds with the aim to highlight their structural diversity and the pharmacological relevance of the moiety to drug activity, insofar as possible. In so doing, emphasis is put on chemical and microbiological properties of such compounds in relation to antibacterial, antifungal and antimalarial activities.

Isopropoxy Benzene Guanidine Kills Staphylococcus aureus Without Detectable Resistance

Serious infections caused by multidrug-resistant Staphylococcus aureus clearly urge the development of new antimicrobial agents. Drug repositioning has emerged as an alternative approach that enables us to rapidly identify effective drugs. We first reported a guanidine compound, isopropoxy benzene guanidine, had potent antibacterial activity against S. aureus. Unlike conventional antibiotics, repeated use of isopropoxy benzene guanidine had a lower probability of resistance section. We found that isopropoxy benzene guanidine triggered membrane damage by disrupting the cell membrane potential and cytoplasmic membrane integrity. Furthermore, we demonstrated that isopropoxy benzene guanidine is capable of treating invasive MRSA infections in vivo studies. These findings provided strong evidence that isopropoxy benzene guanidine represents a new chemical lead for novel antibacterial agent against multidrug-resistant S. aureus infections.

Arylbiamidines: synthesis and structural studies en route to anticancer applications

Four novel arylbiamidine series were studied showing particular tautomerism and H-bonding structure highlighting their promising druglike features toward anticancer applications.

The Structure, Function, and Mechanisms of Action of Enterovirus Non-structural Protein 2C

Enteroviruses are a group of RNA viruses belonging to the family Picornaviridae. They include human enterovirus groups A, B, C, and D as well as non-human enteroviruses. Enterovirus infections can lead to hand, foot, and mouth disease and herpangina, whose clinical manifestations are often mild, although some strains can result in severe neurological complications such as encephalitis, myocarditis, meningitis, and poliomyelitis. To date, research on enterovirus non-structural proteins has mainly focused on the 2A and 3C proteases and 3D polymerase. However, another non-structural protein, 2C, is the most highly conserved protein, and plays a vital role in the enterovirus life cycle. There are relatively few studies on this protein. Previous studies have demonstrated that enterovirus 2C is involved in virus uncoating, host cell membrane rearrangements, RNA replication, encapsidation, morphogenesis, ATPase, helicase, and chaperoning activities. Despite ongoing research, little is known about the pathogenesis of enterovirus 2C proteins in viral replication or in the host innate immune system. In this review, we discuss and summarize the current understanding of the structure, function, and mechanism of the enterovirus 2C proteins, focusing on the key mutations and motifs involved in viral infection, replication, and immune regulation. We also focus on recent progress in research into the role of 2C proteins in regulating the pattern recognition receptors and type I interferon signaling pathway to facilitate viral replication. Given these functions and mechanisms, the potential application of the 2C proteins as a target for anti-viral drug development is also discussed. Future studies will focus on the determination of more crystal structures of enterovirus 2C proteins, which might provide more potential targets for anti-viral drug development against enterovirus infections.

Sulfonylguanidine Derivatives as Potential Antimelanoma Agents

Sulfonylguanidines are interesting bioactive compounds with a broad range of applications in the treatment of different pathologies. 2-Aminobenzazole-based structures are well employed in the development of new anticancer drugs. Two series of novel N-benzazol-2-yl-N'-sulfonyl guanidine derivatives were synthesized with the sulfonylguanidine in either an extra- or intracyclic frame. They were evaluated for their antiproliferative activity against malignant melanoma tumor cells, thus allowing structure-activity relationships to be defined. Additionally, NCI-60 screening was performed for the best analogue to study its efficiency against a panel of other cancer cell lines. The stability profile of this promising compound was then validated. During the synthetic process, an unexpected new deamidination of the sulfonylguanidine towards sulfonamide function was also identified.

Prediction of explosive properties of newly synthesized amino nitroguanidine-based energetic complexes via density functional theory

Density functional theory calculations were performed to explore four octahedral energetic complexes including [CoCl₂ (ANQ)₂], [Co (ANQ)₂(H2O)₂]²⁺, [CuCl₂ (ANQ)₂], and [Cu(NO3)₂ (ANQ)₂], (ANQ = amino nitroguanidine). In this work, an attempt has been made to present useful structural data in order to investigate and predict the explosive properties of these complexes. In this regard, interaction energy (IE), natural bond orbital (NBO), atoms in a molecule (AIM) as well as the three-dimensional Hirshfeld surface analysis and the two-dimensional fingerprint plots, charge transfers, HUMO-LUMO gap, oxygen balance (%OB) amounts, and molecular electrostatic potential (MEP) maps were utilized to assign intermolecular interactions, bond lengths, the nature of metal-ligand bonds, and energies in subject compounds. The results reveal that among the five applied levels of theory, interaction energies obtaining from M06-2X/Def2TZVP were in excellent compliance with the experiments. Additionally, the N⋯O interaction, oxygen balance, density, and HOMO-LUMO gap were the most contributing factors in assigning sensitivity and detonation properties. In general, the sensitivity and detonation properties are increased in the following order: ANQ < complex1 < complex3 < complex2 < complex4. Graphical abstract.

Discovery and Pharmacokinetics of Sulfamides and Guanidines as Potent Human Arginase 1 Inhibitors

We designed and synthesized a series of arginase inhibitors as derivatives of the well-known 2-(S)-amino-6-boronohexanoic acid (ABH) with basic and neutral side chains in the α-position relative to the amino acid group. In an effort to improve the pharmacokinetic profile of literature examples and retain potent enzymatic activity, sulfamido moieties were introduced to generate hydrogen bond interaction with the aspartic acid residue in the arginase active site. The compounds with basic guanidine-containing side chains were even more potent arginase inhibitors. Both groups of compounds, as designed, demonstrated low clearance in their pharmacokinetic profile. The most active inhibitor 15aa showed high nanomolar potency with IC50 = 32 nM toward human arginase 1 and demonstrated low clearance (4.2 mL/min/kg), long t 1/2, and moderate volume of distribution in rat pharmacokinetic studies.

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).

Synthetic Approaches to a Challenging and Unusual Structure—An Amino-Pyrrolidine Guanine Core

The synthesis of an unreported 2-aminopyrrolidine-1-carboxamidine unit is here described for the first time. This unusual and promising structure was attained through the oxidative decarboxylation of amino acids using the pair of reagents, silver(I)/peroxydisulfate (Ag(I)/S₂O₈²⁻) followed by intermolecular (in the case of l-proline derivative) and intramolecular trapping (in the case of acyl l-arginine) by N-nucleophiles. The l-proline approach has a broader scope for the synthesis of 2-aminopyrrolidine-1-carboxamidine derivatives, whereas the intramolecular cyclization afforded by the l-acylarginines, when applied, results in higher yields. The former allowed the first synthesis of cernumidine, a natural alkaloid isolated in 2011 from Solanum cernuum Vell, as its racemic form.

In vitro Antibacterial Activity of Isopropoxy Benzene Guanidine Against Multidrug-Resistant Enterococci

Background

Bacterial infections cause a serious public health crisis due to the emergence of resistance towards multiple conventional antibacterial drugs. In particular, multidrug-resistant (MDR) Enterococcus faecium which belongs to "ESKAPE" organisms is causing significant problems worldwide. Hence, there is an urgent need to find alternative therapies. Recently, substituted benzene guanidine compounds have been used as lead structures to discover new promising drugs in both synthetic and medicinal chemistry.

Purpose

Here we investigated the antimicrobial activity of a new substituted benzene guanidine analog, isopropoxy benzene guanidine, against Enterococci.

Material and methods

The isopropoxy benzene guanidine was synthesized by Guangzhou Insighter Biotechnology Co., Ltd and tested on both reference bacterial strain and 32 clinical MDR Enterococci strains. The in vitro antibacterial activity was evaluated by microdilution method and kill kinetic assays. The potential antibacterial mechanism was measured by fluorescence spectrometry using fluorescent membrane potential probe 3, 3-diethyloxacarbocyanine iodide (DiOC₂ (3)).

Results

Isopropoxy benzene guanidine exhibited potent bactericidal activity against both reference strain and MDR Enterococci isolates. The minimum inhibitory concentration (MIC) range for isopropoxy benzene guanidine was 1-4 μg/mL. Minimum bactericidal concentration (MBC) was about 2-8-fold of its MIC values. Time-kill studies showed that isopropoxy benzene guanidine provided superior bactericidal effect against reference and MDR strains within 12 hrs at 2×MIC. Furthermore, isopropoxy benzene guanidine could cause a large reduction in the magnitude of the generated membrane potential compared to that of the untreated cells.

Conclusion

The present study highlights the potent bactericidal activity of isopropoxy benzene guanidine on Enterococci by disrupting the cell membrane potential. These findings demonstrate that isopropoxy benzene guanidine may be a good chemical lead for further medicinal chemistry and pharmaceutical development and could be used as a therapeutic agent for infectious diseases caused by MDR Enterococci.

Ebola virus VP35 has novel NTPase and helicase-like activities

Ebola virus (EBOV) is a non-segmented, negative-sense RNA virus (NNSV) in the family Filoviridae, and is recognized as one of the most lethal pathogens in the planet. For RNA viruses, cellular or virus-encoded RNA helicases play pivotal roles in viral life cycles by remodelling viral RNA structures and/or unwinding viral dsRNA produced during replication. However, no helicase or helicase-like activity has ever been found to associate with any NNSV-encoded proteins, and it is unknown whether the replication of NNSVs requires the participation of any viral or cellular helicase. Here, we show that despite of containing no conserved NTPase/helicase motifs, EBOV VP35 possesses the NTPase and helicase-like activities that can hydrolyse all types of NTPs and unwind RNA helices in an NTP-dependent manner, respectively. Moreover, guanidine hydrochloride, an FDA-approved compound and inhibitor of certain viral helicases, inhibited the NTPase and helicase-like activities of VP35 as well as the replication/transcription of an EBOV minigenome replicon in cells, highlighting the importance of VP35 helicase-like activity during EBOV life cycle. Together, our findings provide the first demonstration of the NTPase/helicase-like activity encoded by EBOV, and would foster our understanding of EBOV and NNSVs.

The antibiotic robenidine exhibits guanabenz-like cytoprotective properties by a mechanism independent of protein phosphatase PP1:PPP1R15A

The aminoguanidine compound robenidine is widely used as an antibiotic for the control of coccidiosis, a protozoal infection in poultry and rabbits. Interestingly, robenidine is structurally similar to guanabenz (analogs), which are currently undergoing clinical trials as cytoprotective agents for the management of neurodegenerative diseases. Here we show that robenidine and guanabenz protect cells from a tunicamycin-induced unfolded protein response to a similar degree. Both compounds also reduced the tumor necrosis factor α-induced activation of NF-κB. The cytoprotective effects of guanabenz (analogs) have been explained previously by their ability to maintain eIF2α phosphorylation by allosterically inhibiting protein phosphatase PP1:PPP1R15A. However, using a novel split-luciferase-based protein-protein interaction assay, we demonstrate here that neither robenidine nor guanabenz disrupt the interaction between PPP1R15A and either PP1 or eIF2α in intact cells. Moreover, both drugs also inhibited the unfolded protein response in cells that expressed a nonphosphorylatable mutant (S51A) of eIF2α. Our results identify robenidine as a PP1:PPP1R15A-independent cytoprotective compound that holds potential for the management of protein misfolding-associated diseases.

Novel Guanidine Compound against Multidrug-Resistant Cystic Fibrosis-Associated Bacterial Species

Chronic pulmonary infection is a hallmark of lung disease in cystic fibrosis (CF). Infections dominated by non-fermentative Gram-negative bacilli are particularly difficult to treat and highlight an urgent need for the development of new class of agents to combat these infections. In this work, a small library comprising thiourea and guanidine derivatives with low molecular weight was designed; these derivatives were studied as antimicrobial agents against Gram-positive, Gram-negative, and a panel of drug-resistant clinical isolates recovered from patients with CF. One novel compound, a guanidine derivative bearing adamantane-1-carbonyl and 2-bromo-4,6-difluouro-phenyl substituents (H-BDF), showed potent bactericidal activity against the strains tested, at levels generally higher than those exhibited by tobramycin, ceftazimide and meropenem. The role that different substituents exert in the antimicrobial activity has been determined, highlighting the importance of the halo-phenyl group in the guanidine moiety. The new compound displays low levels of cytotoxicity against THP-1 and A549 cells with a selective index (SI) > 8 (patent application PCT/IB2017/054870, August 2017). Taken together, our results indicate that H-BDF can be considered as a promising antimicrobial agent.

Human Norovirus NS3 Has RNA Helicase and Chaperoning Activities

RNA-remodeling proteins, including RNA helicases and chaperones, act to remodel RNA structures and/or protein-RNA interactions and are required for all processes involving RNAs. Although many viruses encode RNA helicases and chaperones, their in vitro activities and their roles in infected cells largely remain elusive. Noroviruses are a diverse group of positive-strand RNA viruses in the family Caliciviridae and constitute a significant and potentially fatal threat to human health. Here, we report that the protein NS3 encoded by human norovirus has both ATP-dependent RNA helicase activity that unwinds RNA helices and ATP-independent RNA-chaperoning activity that can remodel structured RNAs and facilitate strand annealing. Moreover, NS3 can facilitate viral RNA synthesis in vitro by norovirus polymerase. NS3 may therefore play an important role in norovirus RNA replication. Lastly, we demonstrate that the RNA-remodeling activity of NS3 is inhibited by guanidine hydrochloride, an FDA-approved compound, and, more importantly, that it reduces the replication of the norovirus replicon in cultured human cells. Altogether, these findings are the first to demonstrate the presence of RNA-remodeling activities encoded by Caliciviridae and highlight the functional significance of NS3 in the noroviral life cycle.IMPORTANCE Noroviruses are a diverse group of positive-strand RNA viruses, which annually cause hundreds of millions of human infections and over 200,000 deaths worldwide. For RNA viruses, cellular or virus-encoded RNA helicases and/or chaperones have long been considered to play pivotal roles in viral life cycles. However, neither RNA helicase nor chaperoning activity has been demonstrated to be associated with any norovirus-encoded proteins, and it is also unknown whether norovirus replication requires the participation of any viral or cellular RNA helicases/chaperones. We found that a norovirus protein, NS3, not only has ATP-dependent helicase activity, but also acts as an ATP-independent RNA chaperone. Also, NS3 can facilitate in vitro viral RNA synthesis, suggesting the important role of NS3 in norovirus replication. Moreover, NS3 activities can be inhibited by an FDA-approved compound, which also suppresses norovirus replicon replication in human cells, raising the possibility that NS3 could be a target for antinoroviral drug development.

One-pot synthesis of diverseN,N′-disubstituted guanidines fromN-chlorophthalimide, isocyanides and aminesvia N-phthaloyl-guanidines

A sequential one-pot approach towardsN,N′-disubstituted guanidines fromN-chlorophthalimide, isocyanides and amines is reported.

Marine Terpenoid Diacylguanidines: Structure, Synthesis, and Biological Evaluation of Naturally Occurring Actinofide and Synthetic Analogues

A new diacylguanidine, actinofide (1), has been isolated from the marine mollusk Actinocyclus papillatus. The structure, exhibiting a guanidine moiety acylated by two terpenoid acid units, has been established by spectroscopic methods and secured by synthesis. Following this, a series of structural analogues have been synthesized using the same procedure. All of the compounds have been evaluated in vitro for the growth inhibitory activity against a variety of cancer cell lines.

Modification and Functionalization of the Guanidine Group by Tailor-made Precursors

The guanidine group is one of the most important pharmacophoric groups in medicinal chemistry. The only amino acid carrying a guanidine group is arginine. In this article, an easy method for the modification of the guanidine group in peptidic ligands is provided, with an example of RGD-binding integrin ligands. It was recently demonstrated that the distinct modification of the guanidine group in these ligands allows for the selective modulation of the subtype (e.g., between the subtypes αv and α5). Moreover, a formerly unknown strategy for the functionalization via the guanidine group was demonstrated, and the synthetic approach is reviewed in this document. The modifications described here involve terminally (Nω) alkylated and acetylated guanidine groups. For the synthesis, tailor-made precursor molecules are synthesized, which are then subjected to a reaction with an orthogonally deprotected amine to transfer the pre-modified guanidine group. For the synthesis of alkylated guanidines, precursors based on N,N'-Di-Boc-1H-pyrazole-1-carboxamidine are used to synthesize acylated compounds, the precursor of choice being a correspondingly acylated derivative of N-Boc-S-methylisothiourea, which can be obtained in one- and two-step reactions.