Cyclosquaramides as Kinase Inhibitors with Anticancer Activity

Reaction contest: hydrolysis versus intramolecular cyclisation reaction in alkyl squaramate esters

The stability and hydrolytic behavior of squaramate esters in aqueous solutions have been investigated. The structure of squaramates and the nature of adjacent groups significantly influence their aqueous stability and reactivity towards nucleophiles. Squaramate esters, lacking or containing weakly basic neighboring group participation (NGP) substitutions, remain stable up to pH 9. Their hydrolysis rate (k OH ≈ 10-1 M-1 s-1) is 1000 times faster than that of squaramides, following a second-order rate law. Squaramate esters functionalized with basic NGP groups, such as amines, display a pH-dependent hydrolysis rate due to anchimeric assistance of the terminal amino group, reducing stability to pH 5. However, when the squaramate ester has a terminal nucleophilic group in the γ position of the alkyl chain, it undergoes rapid intramolecular cyclization, forming cyclic squaramides.

Oxocarbon Acids and their Derivatives in Biological and Medicinal Chemistry

The biological and medicinal chemistry of the oxocarbon acids 2,3- dihydroxycycloprop-2-en-1-one (deltic acid), 3,4-dihydroxycyclobut-3-ene-1,2-dione (squaric acid), 4,5-dihydroxy-4-cyclopentene-1,2,3-trione (croconic acid), 5,6-dihydroxycyclohex- 5-ene-1,2,3,4-tetrone (rhodizonic acid) and their derivatives is reviewed and their key chemical properties and reactions are discussed. Applications of these compounds as potential bioisosteres in biological and medicinal chemistry are examined. Reviewed areas include cell imaging, bioconjugation reactions, antiviral, antibacterial, anticancer, enzyme inhibition, and receptor pharmacology.

Are patents important indicators of innovation for Chagas disease treatment?

INTRODUCTION

Chagas disease is a neglected, endemic disease in 21 countries, spreading to non-endemic countries too. Like other neglected diseases affecting primarily low- and middle-income countries, low investment and the absence of new chemical entities from the industry occurred. Increased knowledge about the parasite, drug targets, and vector control has been observed, but this was not translated into new drugs. The partnerships of pharmaceutical companies with academies and consolidated networks to increment the new drugs and treatment research in Chagas disease are shown. The current review analyzes in detail the patents dealing with compounds candidates for new drugs and treatment. The patent search was performed using Orbit Intelligence® software in the 2001-2021 period.

AREAS COVERED

The author focused specifically on patents for the treatment, the new candidates disclosed in the patents, and the barriers to innovation.

EXPERT OPINION

Patents in Chagas disease have been increasing in the last years, although they do not bring new compounds to an effective treatment.

Synthesis and Antiplasmodial Activity of Bisindolylcyclobutenediones

Malaria is one of the most dangerous infectious diseases. Because the causative Plasmodium parasites have developed resistances against virtually all established antimalarial drugs, novel antiplasmodial agents are required. In order to target plasmodial kinases, novel N-unsubstituted bisindolylcyclobutenediones were designed as analogs to the kinase inhibitory bisindolylmaleimides. Molecular docking experiments produced favorable poses of the unsubstituted bisindolylcyclobutenedione in the ATP binding pocket of various plasmodial protein kinases. The synthesis of the title compounds was accomplished by sequential Friedel-Crafts acylation procedures. In vitro screening of the new compounds against transgenic NF54-luc P. falciparum parasites revealed a set of derivatives with submicromolar activity, of which some displayed a reasonable selectivity profile against a human cell line. Although the molecular docking studies suggested the plasmodial protein kinase PfGSK-3 as the putative biological target, the title compounds failed to inhibit the isolated enzyme in vitro. As selective submicromolar antiplasmodial agents, the N-unsubstituted bisindolylcyclobutenediones are promising starting structures in the search for antimalarial drugs, albeit for a rational development, the biological target addressed by these compounds has yet to be identified.

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.

Regorafenib analogues and their ferrocenic counterparts: synthesis and biological evaluation

New ferrocene analogues of regorafenib have been prepared and their biological activity was evaluated in kinase and cellular assays.

Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids

The hydrolytic degradation of squaramides and squaramic acids, the product of partial hydrolysis of squaramides, has been evaluated by UV spectroscopy at 37 °C in the pH range 3-10. Under these conditions, the compounds are kinetically stable over long time periods (>100 days). At pH >10, the hydrolysis of the squaramate anions shows first-order dependence on both squaramate and OH^-. At the same temperature and [OH^-], the hydrolysis of squaramides usually displays biphasic spectral changes (A → B → C kinetic model) with formation of squaramates as detectable reaction intermediates. The measured rates for the first step (k₁ ≈ 10^-4 M^-1 s^-1) are 2-3 orders of magnitude faster than those for the second step (k₂ ≈ 10^-6 M^-1 s^-1). Experiments at different temperatures provide activation parameters with values of ΔH^⧧ ≈ 9-18 kcal mol^-1 and ΔS^⧧ ≈ -5 to -30 cal K^-1 mol^-1. DFT calculations show that the mechanism for the alkaline hydrolysis of squaramic acids is quite similar to that of amides.

Effective anti-leishmanial activity of minimalist squaramide-based compounds

In order to evaluate the in vitro leishmanicidal activity of N,N'-Squaramides derivatives, compounds that feature both hydrogen bond donor and acceptor groups and are capable of multiple interactions with complementary sites, against Leishmania infantum, Leishmania braziliensis and Leishmania donovani a series of 18compounds was prepared and assayed on extracellular and intracellular parasite forms. Infectivity and cytotoxicity tests were performed on J774.2 macrophage cells using meglumine antimoniate (Glucantime) as the reference drug. Changes in metabolite excretion by ¹H-NMR and the ultrastructural alterations occurring in the parasites treated using transmission electron microscopy (TEM), was analyzed. Compounds 1, 7, 11, 14 and 17 were the more active and less toxic. Infection rates showed that the order of effectiveness was 17 > 11 > 14 > 7 for both L. infantum and L. braziliensis and in the same way, the compound 1 for L. donovani. All these compounds have altered the typical structure of the promastigotes, glycosomes and mitochondria. These severe modifications by the compounds are the ultimate reasons for the alterations observed in the excretion products. The Squaramide 17 (3-(butylamino)-4-((3-(dimetilamino)propyl)(methyl)amino)cyclobut-3-en-1,2-dione) was clearly the most efficient of all compounds. The data appear to confirm that the severe modifications generated in organelles such as glycosomes or mitochondria by the compounds are the ultimate reasons for the alterations observed in the excretion products of all species. The activity, stability, low cost of starting materials, and straightforward synthesis make amino squaramides appropriate molecules for the development of an affordable anti-leishmanial agent.

Macrocyclic squaramides: anion receptors with high sulfate binding affinity and selectivity in aqueous media

A number of macrocyclic squaramide-containing receptors (MSQs) have been designed and synthesised and their interaction with a range of inorganic anions was studied in solution by ¹H NMR spectroscopy and ESI-HRMS. The binding data revealed remarkable binding of sulfate in aqueous mixtures from 0.5 to 50% v/v H₂O/DMSO-d₆. The larger [3]-MSQs were found to better match the size and shape of the sulfate ion than the [2]-MSQs, providing high affinity and selectivity for sulfate while other tetrahedral divalent anions such as selenate, phosphate species and chromate have substantially lower binding affinities. In mixtures of anions mimicking the composition of either nuclear waste or plasma, the [3]-MSQs were still able to bind sulfate ions with high affinity.

Squaramides with cytotoxic activity against human gastric carcinoma cells HGC-27: synthesis and mechanism of action

A series of squaramates and squaramides have been synthesized and their cytotoxic activity has been investigated in different cancer cell lines.

Naturally occurring bioactive Cyclobutane-containing (CBC) alkaloids in fungi, fungal endophytes, and plants

This article focuses on the occurrence and biological activities of cyclobutane-containing (CBC) alkaloids obtained from fungi, fungal endophytes, and plants. Naturally occurring CBC alkaloids are of particular interest because many of these compounds display important biological activities and possess antitumour, antibacterial, antimicrobial, antifungal, and immunosuppressive properties. Therefore, these compounds are of great interest in the fields of medicine, pharmacology, medicinal chemistry, and the pharmaceutical industry. Fermentation and production of CBC alkaloids by fungi and/or fungal endophytes is also discussed. This review presents the structures and describes the activities of 98 CBC alkaloids.

Cell uptake and localization studies of squaramide based fluorescent probes

Cell internalization is a major issue in drug design. Although squaramide-based compounds are receiving much attention because of their interesting bioactivity, cell uptake and trafficking within cells of this type of compounds are still unknown. In order to monitor the cell internalization process of cyclosquaramide compounds we have prepared two fluorescent probes by covalently linking a fluorescent dye (BODIPY derivative or fluorescein) to a noncytotoxic cyclosquaramide framework. These two probes (C2-BDP and C2-FITC) rapidly internalize across live cell membranes through endocytic receptor-mediated mechanisms. Due to its higher fluorescence and photochemical stability, C2-BDP is a superior dye than C2-FITC. C2-BDP remains sequestered in late endosomes allowing their fast and selective imaging in various live cell types. Cyclosquaramide-cell membrane interactions facilitate cell uptake and have been investigated by binding studies in solution as well as in live cells. Cyclosquaramide 1 (C2-BDP) can be used as a highly fluorescent probe for the rapid and selective imaging of late endosomes in live cells.

Synthesis and biological evaluation of N,N'-squaramides with high in vivo efficacy and low toxicity: toward a low-cost drug against Chagas disease

Access to basic drugs is a major issue in developing countries. Chagas disease caused by Trypanosoma cruzi is a paradigmatic example of a chronic disease without an effective treatment. Current treatments based on benznidazole and nifurtimox are expensive, ineffective, and toxic. N,N'-Squaramides are amide-type compounds that feature both hydrogen bond donor and acceptor groups and are capable of multiple interactions with complementary sites. When combined with amine and carboxylic groups, squaramide compounds have increased solubility and therefore make suitable therapeutic agents. In this work, we introduce a group of Lipinski's rule of five compliant squaramides as candidates for treating Chagas disease. The in vivo studies confirmed the positive expectations arising from the preliminary in vitro studies, revealing compound 17 to be the most effective for both acute and chronic phases. The activity, stability, low cost of starting materials, and straightforward synthesis make amino squaramides appropriate molecules for the development of an affordable anti-Chagasic agent.

Charge transfer (CT) mechanochromism: dramatic CT absorption change of crystalline π-conjugated oligomers containing TCNQ upon mechanical grinding

New π-conjugated oligomers with high crystallinity were prepared from the simple solvothermal reaction of squaric acid and diaminopyrenes.