Expanding the squaramide library as mycobacterial ATP synthase inhibitors: Innovative synthetic pathway and biological evaluation.

Mycobacterial ATP synthase is a validated therapeutic target for combating drug-resistant tuberculosis. Inhibition of this enzyme has been featured as an efficient strategy for the development of new antimycobacterial agents against drug-resistant pathogens. In this study, we synthesised and explored two distinct series of squaric acid analogues designed to inhibit mycobacterial ATP synthase. Among the extensive array of compounds investigated, members of the phenyl-substituted sub-library emerged as primary hits. To gain deeper insights into their mechanisms of action, we conducted advanced biological studies, focusing on the compounds displaying a direct binding of a nitrogen heteroatom to the phenyl ring, resulting in the highest potency. Our investigations into spontaneous mutants led to the validation of a single point mutation within the atpB gene (Rv1304), responsible for encoding the ATP synthase subunit a. This genetic alteration sheds light on the molecular basis of resistance to squaramides. Furthermore, we explored the possibility of synergy between squaramides and the reference drug clofazimine using a checkerboard assay, highlighting the promising avenue for enhancing the effectiveness of existing treatments through combined therapeutic approaches. This study contributes to the expansion of investigating squaramides as promising drug candidates in the ongoing battle against drug-resistant tuberculosis.

Bicyclic N-dihalocyclopropylamide derivatives as precursors of nitrogen-containing fused polycyclic systems.

Examples of carbon-carbon bond-forming cyclisation reactions, involving allyl cations generated by the thermal ring-opening of halocyclopropanes, have been scarcely reported. In this contribution, we are describing the results of a study conducted with N-dihalocyclopropylamide substrates, designed as precursors of cyclic iminium intermediates that were aimed at participating in intramolecular reactions with electron-rich aromatic groups. Competitive side-reactions were identified, and access to the desired polycyclic products was carefully evaluated. The results were found to be strongly dependent on the substitution pattern of the nucleophilic aromatic moieties, as well as on the sizes of the rings of the target products. In spite of the rather moderate yields generally obtained, this approach represents a particularly short and inexpensive route to various interesting nitrogen-containing polycyclic systems, namely benzoindolizidine, benzoquinolizidine, piperidinobenzoazepane and azepanoisoquinoline compounds.

Novel heterocyclic hydroxamates as inhibitors of the mycobacterial zinc metalloprotease Zmp1 to probe its mechanism of function.

Mycobacterial zinc metalloprotease-1 (Zmp1) is an essential enzyme for intracellular survival and pathogenicity of Mycobacterium tuberculosis. However, the exact mechanism of function of this enzyme remains unclear. This paper examines the effect of novel organic molecules on the inhibition of Zmp1. We followed our previous results and synthesised three libraries of new hydroxamates. All compounds were studied for their inhibitory properties towards a recombinant Zmp1 from Mycobacterium tuberculosis by MALDI-TOF MS. Furthermore, a macrophage infection assay was performed to evaluate intracellular antimycobacterial activity. In the whole-cell assay, no direct activity of synthesised heterocyclic hydroxamates was observed against Mycobacterium tuberculosis and Mycobacterium bovis. No acute cellular toxicity was observed against the murine RAW 264.7 macrophage cell line and human MRC-5 lung fibroblast cell line. However, thiazolidinediones 2 showed the dose-dependent inhibition of intracellular survival of Mycobacterium tuberculosis H37Ra. The inhibition was structure-dependent, with the most active derivative 2f inducing an 83.2% reduction of bacterial survival within the macrophage host cell. The promising biological activity confirmed thiazolidinediones 2 as Zmp1 inhibitors that can be used as tool compounds for further exploration of the role of Zmp1 for in vivo pathogenicity. In the long run, thiazolidinediones 2 show the potential to act as a scaffold for Zmp1 inhibitors to target intracellular Mtb as a novel tuberculosis treatment strategy.

Polymer-Supported Synthesis of Various Pteridinones and Pyrimidodiazepinones.

In this report, we employed the solid-phase synthetic approach to prepare variously substituted dihydropteridinones, tetrahydropyrrolopteridinones, and pyrimidodiazepinones, using a versatile building block-4,6-dichloro-5-nitropyrimidine. All these compounds are pharmacologically significant scaffolds of the great importance of medicinal chemists. The fast and efficient synthetic methodology is highly desirable for defining their structure-activity relationship (SAR) and optimizing pharmacokinetic properties. Our research efforts utilize simple synthetic methods to generate a library of analogues for future SAR studies. The efficiency of our approach was exemplified in various pteridinones as well as pyrimidodiazepinones.

Small organic molecules targeting the energy metabolism of Mycobacterium tuberculosis.

Causing approximately 10 million incident cases and 1.3-1.5 million deaths every year, Mycobacterium tuberculosis remains a global health problem. The risk is further exacerbated with latent tuberculosis (TB) infection, the HIV pandemic, and increasing anti-TB drug resistance. Therefore, unexplored chemical scaffolds directed towards new molecular targets are increasingly desired. In this context, mycobacterial energy metabolism, particularly the oxidative phosphorylation (OP) pathway, is gaining importance. Mycobacteria possess primary dehydrogenases to fuel electron transport; aa3-type cytochrome c oxidase and bd-type menaquinol oxidase to generate a protonmotive force; and ATP synthase, which is essential for both growing mycobacteria as well as dormant mycobacteria because ATP is produced under both aerobic and hypoxic conditions. Small organic molecules targeting OP are active against latent TB as well as resistant TB strains. FDA approval of the ATP synthase inhibitor bedaquiline and the discovery of clinical candidate Q203, which both interfere with the cytochrome bc1 complex, have already confirmed mycobacterial energy metabolism to be a valuable anti-TB drug target. This review highlights both preferable molecular targets within mycobacterial OP and promising small organic molecules targeting OP. Progressive research in the area of mycobacterial OP revealed several highly potent anti-TB compounds with nanomolar-range MICs as low as 0.004 µM against Mtb H37Rv. Therefore, we are convinced that targeting the OP pathway can combat resistant TB and latent TB, leading to more efficient anti-TB chemotherapy.

Squaric acid analogues in medicinal chemistry.

In this review, we summarize the published data on squaric acid analogues with a special focus on their use in medicinal chemistry and as potential drugs. Squaric acid is an interesting small molecule with an almost perfectly square shape, and its analogues have a variety of biological activities that are enabled by the presence of significant H-bond donors and acceptors. Unfortunately, most of these compounds also exhibit reactive functionalities, and this deters the majority of medicinal chemists and pharmacologists from trying to use them in drug development. However, this group of compounds is experiencing a renaissance, and large numbers of them are being tested for antiprotozoal, antibacterial, antifungal, and antiviral activities. The most useful of these compounds exhibited IC50 values in the nanomolar range, which makes them promising drug candidates. In addition to these activities, their interactions with living systems were intensively explored, revealing that squaric acid analogues inhibit various enzymes and often serve as receptor antagonists and that the squaric acid moiety may be used as a non-classical isosteric replacement for other functional groups such as carboxylate. In summary, this review is focused on squaric acid and its analogues and their use in medicinal chemistry and should serve as a guide for other researchers in the field to demonstrate the potential of these compounds based on previous research.

Bis-Rhodamine B System as a Tin Detector or Molecular Electronics Device.

In this report, fluorescent systems consisting of two Rhodamine B moieties were designed and synthesized employing the solid-phase synthetic approach. The compounds were tested for their chemosensing behavior upon the addition of various metal ions over UV-vis absorption and fluorescence spectra. Two probes, 1 and 3, exhibited the best affinity to Sn(IV) ions, resulting in strong fluorescence as well as absorbance enhancement with the low detection limits (2.78 and 2.56 µM, respectively). Compound 3 having two excitations as well as emission maxima was used for the construction of the light dimmer with the alarm for detection of too low pH. The system is operated by a change of pH and can be used as a molecular electronic device.

Novel thiazolidinedione-hydroxamates as inhibitors of Mycobacterium tuberculosis virulence factor Zmp1.

Zinc metalloprotease 1 (Zmp1) is an extracellular enzyme, which has been found essential for the intracellular survival and pathogenesis of Mycobacterium tuberculosis. In this work, we designed and synthesized a series of novel thiazolidinedione-hydroxamates and evaluated in silico their drug-likeness behavior. Then, their inhibitory properties towards a recombinant Zmp1 from Mycobacterium tuberculosis were analyzed by MALDI-TOF MS. Nine of the tested compounds were found to inhibit the enzymatic reaction more effectively than the generic metalloprotease inhibitor phosphoramidon. Furthermore, the synthesized thiazolidinedione-hydroxamate hybrids were evaluated for their in vitro antimycobacterial activity and acute cytotoxicity using whole-cell assays. Results showed that none of the hybrids exhibited acute cytotoxicity against RAW264.7 macrophages. Whereas extracellular antimycobacterial activity was limited, RAW264.7 macrophage infection results showed that a majority of the hybrids inhibited the intracellular growth of Mycobacterium tuberculosis at a concentration of 100 and 10 µM. The thiazolidinedione-hydroxamate compound 2n was considered to be the best candidate of the evaluated library.

Synthesis of Various 2-Aminobenzoxazoles: The Study of Cyclization and Smiles Rearrangement.

This study reports two synthetic approaches leading to 2-aminobenzoxazoles and their N-substituted analogues. Our first synthetic strategy involves a reaction between various o-aminophenols and N-cyano-N-phenyl-p-toluenesulfonamide as a nonhazardous electrophilic cyanating agent in the presence of Lewis acid. The second synthetic approach uses the Smiles rearrangement upon activation of benzoxazole-2-thiol with chloroacetyl chloride. Both developed synthetic protocols are widely applicable, afford the desired aminobenzoxazoles in good to excellent yields, and use nontoxic and inexpensive starting material.

Stereo- and regioselectivity of the hetero-Diels-Alder reaction of nitroso derivatives with conjugated dienes.

The hetero-Diels-Alder reaction between a nitroso dienophile and a conjugated diene to give the 3,6-dihydro-2H-1,2-oxazine scaffold is useful for the synthesis of many biologically interesting molecules due to the diverse opportunities created by subsequent transformations of the resulting 1,2-oxazine ring. This review discusses the rationale for the observed regio- and stereoselectivity and the methods developed in recent years used to control and improve the stereo- and regioselectivity for the synthesis of 1,2-oxazine scaffolds.

Synthesis, reactivity and biological activity of 5-alkoxymethyluracil analogues.

This review article summarizes the results of a long-term investigation of 5-alkoxymethyluracil analogues and is aimed, in particular, at methods of syntheses. Most of the presented compounds were synthesized in order to evaluate their biological activity, therefore, a brief survey of biological activity, especially antiviral, cytotoxic and antibacterial, is also reported.

Synthesis of various 5-alkoxymethyluracil analogues and structure-cytotoxic activity relationship study.

A number of 5-alkoxymethyluracil analogues were synthesized to evaluate their cytotoxic activity. 5-Alkoxymethyluracil derivatives 1 were prepared via known nucleophilic substitution of 5-chloromethyluracil 5 and subsequently transformed to their corresponding nucleosides 2. All prepared compounds were submitted to cytotoxic activity testing against drug sensitive and drug resistant leukaemia cells and solid tumour derived cell lines. In addition, the cytotoxic activity of 5-alkoxymethyluracil analogues 1 and 2 was compared with the previously published 5-[alkoxy(4-nitrophenyl)methyl]uracil analogues 3 and 4. Extensive structure-cytotoxic activity relationship studies are reported.

Synthesis of 5-[alkoxy-(4-nitro-phenyl)-methyl]-uridines and study of their cytotoxic activity.

A series of uridine analogues modified at the 5-position with the 5-[alkoxy-(4-nitrophenyl)-methyl] moiety was synthesized. Nucleosides were formed as a mixture of two diastereoisomers, which were separated and tested for their cytotoxic activity in vitro against different cancer cell lines and for antimicrobial activity. Relationships between structure and the above mentioned activities were studied. The cytotoxic activity was slightly increased in some cases by transformation of bases to nucleosides. Depending on the length of the alkyl chain increased cytotoxic and antimicrobial activity were noted. The cytotoxic activity of the nucleosides was not due to cell cycle alterations, DNA and/or RNA synthesis.

Efficient RNA-targeting by the introduction of aromatic stacking in the duplex major groove via 5-(1-phenyl-1,2,3-triazol-4-yl)-2'-deoxyuridines.

Three pyrimidine nucleosides with differently substituted phenyltriazoles attached to the 5-position were prepared by Cu(I)-assisted azide-alkyne cycloadditions (CuAAC) and incorporated into oligonucleotides. Efficient π-π-stacking between two or more phenyltriazoles in the major groove was found to increase the thermal stability of a DNA:RNA duplex significantly. The best stacking, and most stable duplex, was obtained by a sulfonamide substituted derivative.