Novel imidazo[1,2-a]naphthyridinic systems (part 1): synthesis, antiproliferative and DNA-intercalating activities

A comprehensive review of fused imidazonaphthyridine derivatives: Synthetic approaches and biological applications

Fused heterocyclic imidazonaphthyridine compounds stand at the forefront of global research, captivating remarkable interest in medicinal and synthetic organic chemistry. These compounds possess a range of potent biological and pharmacological properties, rendering them invaluable for medical and therapeutic research, particularly in drug design and discovery. Despite their significance, no dedicated review has focused on fused heterocyclic imidazonaphthyridine derivatives. This comprehensive review aims to consolidate and explore the cutting-edge synthesis approaches tailored specifically for these unique imidazonaphthyridine derivatives. It highlights their current applications in various biological realms and provides insights into potential future trajectories. By steering forthcoming research endeavours towards innovative design and synthesis of novel imidazonaphthyridines, this review seeks to diversify these compounds, paving the way for biological applications that have yet to be fully realized. Overall, as a burgeoning area of research, this review underscores the potential of imidazonaphthyridines as promising candidates for biomedical applications, offering a snapshot of current research and suggesting future avenues for investigation.

One Pot Synthesis of C3-Sulfurized Imidazolo [1,2-a] Pyridines

A facile and efficient annulation strategy was developed from easily accessible a-bromoketones, aminopyridines and benzazol, which afforded a series of imidazole [1,2-a]pyridine sulfides in moderate to good yields. The reaction involves the formation of C-N/C-S bond with the advantages of easy operation and wide substrates scope.

Novel hydrazone-isatin derivatives as potential EGFR inhibitors: Synthesis and in vitro pharmacological profiling

Merging isatin and arylhydrazone moieties constitutes an efficient strategy to access new potential anticancer derivatives. Consequently, 14 hydrazone-isatin derivatives were synthesized and evaluated for their antiproliferative activity against the NCI-60 cancer cell line panel. A kinase assay demonstrated that compound VIIIb inhibited the epidermal growth factor receptor (EGFR), which was confirmed by docking studies, molecular dynamics, and binding free energy calculations. Further characterizations showed that this compound possesses drug-likeness properties, showed a significant decrease of the cell population in the G2/M phase and led to a significant increase in early and late apoptosis, comparable to erlotinib. Also, VIIIb increased the expression of caspase-3 and Bax and decreased the expression of Bcl-2, confirming its potential as a new proapoptotic compound.

Discovery and evaluation of aza-fused tricyclic derivatives for detection of Tau pathology in Alzheimer's disease

For various neurodegenerative diseases, including Alzheimer's disease (AD), the abnormal aggregation of Tau is not only the predominant contributing factor but also a major biomarker for disease diagnosis. In this study, a series of aza-fused tricyclic derivatives were designed and synthesized. By changing the position and number of nitrogen atoms on the fused tricyclic core, the imidazonaphthyridine scaffold was screened and reported for the first time which could potentially detect Tau aggregates. Through a series of in vitro and in vivo biological evaluations, probe [125I]5 possessed exceptional binding affinity (IC50 = 1.63 nM) to neurofibrillary tangles in the AD brain, high selectivity over Aβ plaques (23.4-fold), clean off-target profile to monoamine oxidase A/B (MAO-A/B), and suitable pharmacokinetics (initial brain uptake = 3.22% ID/g).

Regioselective Oxidative Cross-Coupling Reaction: Synthesis of Imidazo[1,2-a]pyridine Fluorophores

A rapid access to a series of N-heteroarene fluorophores has been developed on the basis of the palladium-catalyzed direct oxidative C–H/C–H coupling of imidazo[1,2-a]pyridines with thiophenes/furans. The photophysical properties–structure relationship was systematically investigated. The resulting N-heteroarene fluorophores present color-tunable emissions (λem: 431–507 nm in CH2Cl2) and high fluorescence quantum yields (up to 91% in CH2Cl2).

A Comprehensive Review on Fused Heterocyclic as DNA Intercalators: Promising Anticancer Agents

Since the discovery of DNA intercalating agents (by Lerman, 1961), a growing number of organic, inorganic, and metallic compounds have been developed to treat life-threatening microbial infections and cancers. Fused-heterocycles are amongst the most important group of compounds that have the ability to interact with DNA. DNA intercalators possess a planar aromatic ring structure that inserts itself between the base pairs of nucleic acids. Once inserted, the aromatic structure makes van der Waals interactions and hydrogen-bonding interactions with the base pairs. The DNA intercalator may also contain an ionizable group that can form ionic interactions with the negatively charged phosphate backbone. After the intercalation, other cellular processes could take place, leading ultimately to cell death. The heterocyclic nucleus present in the DNA intercalators can be considered as a pharmacophore that plays an instrumental role in dictating the affinity and selectivity exhibited by these compounds. In this work, we have carried out a revision of small organic molecules that bind to the DNA molecule via intercalation and cleaving and exert their antitumor activity. A general overview of the most recent results in this area, paying particular attention to compounds that are currently under clinical trials, is provided. Advancement in spectroscopic techniques studying DNA interaction can be examined in-depth, yielding important information on structure-activity relationships. In this comprehensive review, we have focused on the introduction to fused heterocyclic agents with DNA interacting features, from medicinal point of view. The structure-activity relationships points, cytotoxicity data, and binding data and future perspectives of medicinal compounds have been discussed in detail.

Spectroscopic Studies on the Interaction of Naphthyridines with DNA and Fluorescent Detection of DNA in Agarose Gel

Four new naphthyridine derivatives (R1-R4) possessing amino acid or boronic acid moieties have been synthesized and characterized using ¹H and ¹³C NMR, FT-IR, and mass spectral techniques. The mechanism of binding of these probes with calf thymus DNA (CT-DNA) has been delineated through UV-Vis, fluorescence, and circular dichroism (CD) spectral techniques along with thermodynamic and molecular docking studies. Small hypochromicity in absorption maximum of the probes without any shift in wavelength of absorption suggests groove binding mode of interaction of these probes with CT-DNA, confirmed by CD and 1H NMR spectral data competitive binding assay with ethidium bromide (EB). CT-DNA quenches the fluorescence of these probes via a static quenching mechanism. In the case of R1 and R4, the observed ΔH^o < 0 and ΔS^o > 0suggest that these probes interact with CT-DNA through H-bonding and hydrophobic interactions, while in the interaction of R2 and R3, van der Walls and H-boding forces are found to be dominant (ΔH^o < 0 and ΔS^o < 0). Results of molecular docking investigations corroborate well with that of spectral studies, and these probes bind in the minor groove of DNA. These probes are found to be effective fluorescent staining agents for DNA in agarose gel in gel electrophoresis experiment with sensitivity comparable to that of EB, and DNA amounts as low as 37.5 ng are visually detectable in the gel.

Fused 1,5-Naphthyridines: Synthetic Tools and Applications

Heterocyclic nitrogen compounds, including fused 1,5-naphthyridines, have versatile applications in the fields of synthetic organic chemistry and play an important role in the field of medicinal chemistry, as many of them have a wide range of biological activities. In this review, a wide range of synthetic protocols for the construction of this scaffold are presented. For example, Friedländer, Skraup, Semmlere-Wolff, and hetero-Diels-Alder, among others, are well known classical synthetic protocols used for the construction of the main 1,5-naphthyridine scaffold. These syntheses are classified according to the nature of the cycle fused to the 1,5-naphthyridine ring: carbocycles, nitrogen heterocycles, oxygen heterocycles, and sulphur heterocycles. In addition, taking into account the aforementioned versatility of these heterocycles, their reactivity is presented as well as their use as a ligand for metal complexes formation. Finally, those fused 1,5-naphthyridines that present biological activity and optical applications, among others, are indicated.

Synthesis of fused imidazo[1,2-a]pyridines derivatives through cascade C(sp2)-H functionalizations

An efficient and convenient synthesis of diversely substituted naphtho[1',2':4,5]imidazo[1,2-a]-pyridine derivatives from the cascade reactions of 2-arylimidazo[1,2-a]pyridines with a-diazo carbonyl compounds via Rh(iii)-catalyzed regioselective C(sp2)-H alkylation followed by intramolecular annulation is presented. Interestingly, when simple 2-arylimidazo[1,2-a]pyridines were used as the substrates, 5,6-disubstituted naphtho[1',2':4,5]imidazo[1,2-a]pyridines were efficiently obtained, whereas using 2-arylimidazo[1,2-a]pyridine-3-carbaldehydes as the substrates afforded naphtho[1',2':4,5]imidazo[1,2-a]-pyridine-5-carboxylates as the dominating products. Compared with literature methods for the synthesis of naphtho[1',2':4,5]imidazo[1,2-a]pyridine derivatives, the protocol presented herein has advantages such as easily obtainable substrates, simple operational procedure, high efficiency and excellent regio- and chemoselectivity.

Metal-free C–N bond formations: one-pot synthesis of pyrido[2′,1′:2,3]imidazo[4,5-c]cinnolines, benzo[4′,5']thiazolo- and thiazolo[2′,3′:2,3]imidazo[4,5-c]cinnolines

An efficient one-pot synthesis of novel pyrido[2′,1′:2,3]imidazo[4,5-c]cinnoline derivatives has been achieved with moderate to good yields, with two C–N bond formations through C–H functionalization of 2-arylimidazo[1,2-a]pyridines.

Synthesis of Naphtho[1',2':4,5]imidazo[1,2-a]pyridines and Imidazo[5,1,2-cd]indolizines Through Pd-Catalyzed Cycloaromatization of 2-Phenylimidazo[1,2-a]pyridines with Alkynes

In this paper, palladium-catalyzed oxidative cycloaromatization of 2-phenylimidazo[1,2-a]pyridine (PIP) with internal alkyne is studied. From this reaction, two classes of fused N-heterocycle, naphtho[1',2':4,5]imidazo[1,2-a]pyridine (NIP) and imidazo[5,1,2-cd]indolizine (IID), were formed through dehydrogenative coupling featured with cleavage of the C-H bonds located on different moiety of the PIP substrates. Moreover, when 5-methyl-2-phenylimidazo [1,2-a]pyridine or 2-mesitylimidazo[1,2-a]pyridine was used, either NIP or IID could be obtained as an exclusive product with good efficiency. Intriguingly, Pd(II) showed different action mode in promoting this reaction compared with Rh(III) and led to the formation of NIP with reversed regio-selectivity for the reaction of asymmetrical alkyne.

Pyrido-imidazodiazepinones as a new class of reversible inhibitors of human kallikrein 7

The human tissue kallikrein-7 (KLK7) is a chymotryptic serine protease member of tissue kallikrein family. KLK7 is involved in skin homeostasis and inflammation. Excess of KLK7 activity is also associated with tumor metastasis processes, especially in ovarian carcinomas, prostatic and pancreatic cancers. Development of Kallikrein 7 inhibitors is thus of great interest in oncology but also for treating skin diseases. Most of the developed synthetic inhibitors present several drawbacks such as poor selectivity and unsuitable physico-chemical properties for in vivo use. Recently, we described a practical sequence for the synthesis of imidazopyridine-fused [1,3]-diazepines. Here, we report the identification of pyrido-imidazodiazepinone core as a new potential scaffold to develop selective and competitive inhibitors of kallikrein-related peptidase 7. Structure-activity relationships (SAR), inhibition mechanisms and selectivity as well as cytotoxicity against selected cancer cell lines were investigated.

Microwave-assisted C–N and C–S bond-forming reactions: an efficient three-component domino sequence for the synthesis of sulfoether-decorated imidazo[1,2-a]pyridines

Microwave-assisted three-component domino reaction for the synthesis of sulfoether-decorated imidazo[1,2-a]pyridines.

Palladium(0)-catalyzed direct C–H hetero-arylation of 2-arylimidazo [1,2-a]pyridines with (E)-1-(5-bromothiophen-2-yl)-3-arylprop-2-en-1-ones and their anticancer activity

An efficient palladium(0)-catalyzed direct hetero-arylation of imidazo[1,2-a]pyridines at the C-3 position of the imidazole ring has been described.

Microwave assisted novel and regioselective functionalization of imidazopyridines with chromene acetals and β-nitrostyrenes

A facile synthesis of novel functionalized imidazopyridines has been accomplished through the condensation of imidazopyridines with chromene hemiacetals or β-nitro styrenes with high regioselectivity and excellent yields in the presence of a catalytic amount of PTSA or InCl₃.

Synthesis and anti-Candida activity of novel 2-hydrazino-1,3-thiazole derivatives

Eighteen new hydrazino-1,3-thiazole derivatives were evaluated against 8 strains of multi-resistant Candida spp. Introduction of an indolyl moiety linked to the hydrazone function enhanced the in vitro anti-Candida activity, with an activity spectrum towards Candida albicans strains. Introduction of a (S)-2-aminoethyl chain on the thiazole nucleus largely enhanced the in vitro antifungal activity, with a selectivity oriented towards non-C. albicans species.

New imidazo[1,2-a]pyridines carrying active pharmacophores: synthesis and anticonvulsant studies

Five new series of imidazo[1,2-a]pyridines carrying biologically active pyrazoline (4a-e), cyanopyridone (5a, b), cyanopyridine (6a-f), 2-aminopyrimidine (7a-f) and pyrimidine-2-thione (8a-d) systems were designed and synthesized as prominent anticonvulsant agents. The target compounds were screened for their in vivo anticonvulsant activity following maximal electroshock (MES) and subcutaneous pentylene tetrazole (scPTZ) methods at a small test dose of 10 mg/kg. Further, Rotarod toxicity method was used to study the toxicity profile of selected compounds. Compounds 4b, 5a, 5b, 6a, 7e and 8d possessing 4-fluorophenyl substituent at 2nd position of imidazo[1,2-a]pyridine ring displayed potent anticonvulsant activity without displaying any toxicity. Enhanced activity profile was observed for new compounds in PTZ method over MES method.

Synthesis and Characterisation of Novel N Substituted 2-Methylimidazo[1,2a]Pyridine-3-Carboxamides

A series of novel N substituted 2-methylimidazo[1,2a]pyridine-3-carboxamides has been synthesised in high yield by a convenient method and characterised by 1H NMR, MS, IR and elemental analysis

Recent developments in the chemistry of deoxyribonucleic acid (DNA) intercalators: principles, design, synthesis, applications and trends

In the present overview, we describe the bases of intercalation of small molecules (cationic and polar neutral compounds) in DNA. We briefly describe the importance of DNA structure and principles of intercalation. Selected syntheses, possibilities and applications are shown to exemplify the importance, drawbacks and challenges in this pertinent, new, and exciting research area. Additionally, some clinical applications (molecular processes, cancer therapy and others) and trends are described.