Compounds with potentialities as novel chemotherapeutic agents in leishmaniasis at preclinical level

Leishmaniasis are neglected infectious diseases caused by kinetoplastid protozoan parasites from the genus Leishmania. These sicknesses are present mainly in tropical regions and almost 1 million new cases are reported each year. The absence of vaccines, as well as the high cost, toxicity or resistance to the current drugs determines the necessity of new treatments against these pathologies. In this review, several compounds with potentialities as new antileishmanial drugs are presented. The discussion is restricted to the preclinical level and molecules are organized according to their chemical nature, source and molecular targets. In this manner, we present antimicrobial peptides, flavonoids, withanolides, 8-aminoquinolines, compounds from Leish-Box, pyrazolopyrimidines, and inhibitors of tubulin polymerization/depolymerization, topoisomerase IB, proteases, pteridine reductase, N-myristoyltransferase, as well as enzymes involved in polyamine metabolism, response against oxidative stress, signaling pathways, and sterol biosynthesis. This work is a contribution to the general knowledge of these compounds as antileishmanial agents.

Review on Isatin- A Remarkable Scaffold for Designing Potential Therapeutic Complexes and Its Macrocyclic Complexes with Transition Metals

Role of synthetic coordination chemistry in pharmaceutical science is expeditiously increased due to its sundry relevances in this field. The present review endows the synthesized macrocyclic complexes of transition metal ions containing isatin and its derivatives as ligand precursors, their characterization and their copious pharmaceutical applications. Isatin (1H-Indole-2,3-dione) is a protean compound (presence of lactam and keto moiety permits to change its molecular framework) that can be obtained from marine animals, plants, and is also found in mammalian tissues and in human fluids as a metabolite of amino acids. It can be used for the synthesis of miscellaneous organic and inorganic complexes and for designing of drugs since it has remarkable utility in pharmaceutical industry due to its wide range of biological and pharmacological activities, for instance anti-microbial, anti-HIV, anti-tubercular, anti-cancer, anti-viral, anti-oxidant, anti-inflammatory, anti-angiogenic, analgesic activity, anti-Parkinson's disease, anti-convulsant etc. This review provides extensive information about the latest methods for the synthesis of isatin or its substituted derivatives based macrocyclic complexes of transition metals and their plentiful applications in medicinal chemistry.

Graphical Abstract

The Bioactivity of Xylene, Pyridine, and Pyrazole Aza Macrocycles against Three Representative Leishmania Species

Due to the urgent need for finding effective and free of secondary effect treatments for every clinical form of Leishmaniasis, a series of synthetic xylene, pyridine and, pyrazole azamacrocycles were tested against three Leishmania species. A total of 14 compounds were tested against J774.2 macrophage cells which were models for host cells, and against promastigote and amastigote forms of each studied Leishmania parasite. Amongst these polyamines, one proved effective against L. donovani, another one for L. braziliensis and L. infantum, and another one was selective solely for L. infantum. These compounds showed leishmanicidal activity and reduced parasite infectivity and dividing ability. Action mechanism studies gave a hint that compounds were active against Leishmania due to their ability to alter parasite metabolic pathways and reduce (except Py33333) parasitic Fe-SOD activity.

Assembly of Polyiodide Networks with Cu(II) Complexes of Pyridinol-Based Tetraaza Macrocycles

Polyiodide networks are currently of great practical interest for the preparation of new electronic materials. The participation of metals in the formation of these networks is believed to improve their mechanical performance and thermal stability. Here we report the results on the construction of polyiodide networks obtained using Cu(II) complexes of a series of pyridinol-based tetraazacyclophanes as countercations. The assembly of these crystalline polyiodides takes place from aqueous solutions on the basis of similar structural elements, the [CuL]²⁺ and [Cu(H_–1L)]⁺ (L = L2, L2-Me, L2-Me₃) complex cations, so that the peculiarities induced by the increase of N-methylation of ligands, the structural variable of ligands, can be highlighted. First, solution equilibria involving ligands and complexes were analyzed (potentiometry, NMR, UV–vis, ITC). Then, the appropriate conditions could be selected to prepare polyiodides based on the above complex cations. Single-crystal XRD analysis showed that the coordination of pyridinol units to two metal ions is a prime feature of these ligands, leading to polymeric coordination chains of general formula {[Cu(H_–1L)]}_nⁿ⁺ (L = L2-Me, L2-Me₃). In the presence of the I^–/I₂ couple, the polymerization tendency stops with the formation of [(CuL)(CuH_–1L)]³⁺ (L = L2-Me, L2-Me₃) dimers which are surrounded by polyiodide networks. Moreover, coordination of the pyridinol group to two metal ions transforms the surface charge of the ring from negative to markedly positive, generating a suitable environment for the assembly of polyiodide anions, while N-methylation shifts the directional control of the assembly from H-bonds to I···I interactions. In fact, an extended concatenation of iodine atoms occurs around the complex dimeric cations, the supramolecular I···I interactions become shorter and shorter, fading into stronger forces dominated by the orbital overlap, which is promising for effective electronic materials.

Polyiodides with high iodine density are generated by Cu(II) complexes of pyridinol-based tetraazacyclophanes. Direct coordination of iodine atoms to Cu(II), anion−π interactions with electron-poor aromatic surfaces, and shift of the directional control of assembly from H-bonds to I···I interactions, governed by N-methylation, are the main elements leading to enhanced iodine chaining and strengthening of I···I contacts.

Stabilisation of Exotic Tribromide (Br3-) Anions via Supramolecular Interaction with A Tosylated Macrocyclic Pyridinophane. A Serendipitous Case

Tetraaza-macrocyclic pyridinophane L-Ts, decorated with a p-toluenesulfonyl (tosyl; Ts) group, appear to be a useful tool to provide evidence on how the interplay of various supramolecular forces can help stabilise exotic anionic species such as tribromide (Br₃⁻) anions. Indeed, crystals of (H₂L-Ts)(Br₃)_1.5(NO₃)_0.5 unexpectedly grew from an acidic (HNO₃) aqueous solution of L-Ts in the presence of Br⁻ anions. The crystal structure of this compound was determined by single crystal XRD analysis. Hydrogen bonds, salt-bridges, anion-π, π-π stacking, and van der Waals interactions contribute to stabilising the crystal lattice. The observation of two independent Br₃⁻ anions stuck over the π-electron densities of pyridine and tosyl ligand groups, one of them being sandwiched between two pyridine rings, corroborates the significance of anion-π interactions for N-containing heterocycles. We show herein the possibility of detecting anion-π contacts from fingerprint plots generated by Hirshfeld surface analysis, demonstrating the effective usage of this structural investigation technique to further dissect individual contributions of stabilising supramolecular forces.

Aromatic and heteroaromatic azacrown compounds: advantages and disadvantages of rigid macrocyclic ligands

Current approaches to the synthesis of aromatic and heteroaromatic azamacrocycles and their derivatives are summarized and systematized. The relationship between the structure of azacrown compounds and their complexation behaviour towards metal cations is analyzed. The diversity of practical applications of azamacrocyclic derivatives in medicine, biology and analytical and organic chemistry, as well as for the design of molecular devices is demonstrated.

The bibliography includes 307 references.

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6-10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.

Stabilization of polyiodide networks with Cu(ii) complexes of small methylated polyazacyclophanes: shifting directional control from H-bonds to I⋯I interactions

Modulation of hydrogen bonds and iodine–iodine interactions, both covalent and supramolecular, unlocks novel possibilities for the construction of transition metal-polyiodide hybrid networks.

Specific and highly efficient condensation of GC and IC DNA by polyaza pyridinophane derivatives

Two bis-polyaza pyridinophane derivatives and their monomeric reference compounds revealed strong interactions with ds-DNA and RNA. The bis-derivatives show a specific condensation of GC- and IC-DNA, which is almost two orders of magnitude more efficient than the well-known condensation agent spermine. The type of condensed DNA was identified as ψ-DNA, characterized by the exceptionally strong CD signals. At variance to the almost silent AT(U) polynucleotides, these strong CD signals allow the determination of GC-condensates at nanomolar nucleobase concentrations. Detailed thermodynamic characterisation by ITC reveals significant differences between the DNA binding of the bis-derivative compounds (enthalpy driven) and that of spermine and of their monomeric counterparts (entropy driven). Atomic force microscopy confirmed GC-DNA compaction by the bis-derivatives and the formation of toroid- and rod-like structures responsible for the ψ-type pattern in the CD spectra.