Cascade synthetic strategies opening access to medicinal-relevant aliphatic 3- and 4-membered N-heterocyclic scaffolds

Synthesis and pharmacological evaluation of natural product diphyllin derivatives against head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is one of the most common malignant tumors, but clinical drug treatments are limited. The natural product diphyllin was identified as a lead compound suppressing the proliferation of HNSCC cells through phenotypic screening of natural product library. However, further developments of diphyllin as an anti-HNSCC agent were restricted by the weak bioactivity and poor metabolic stability. Herein, we designed and synthesized two series of novel diphyllin derivatives that were achieved by introducing various pyranose rings or hydrophilic groups to block the easily metabolic C-4 site with the aim to improve antitumor activity and drug-like properties. Among these compounds, compound A3 showed the most potent inhibitory effects against HNSCC cells with IC50 values ranging from 4.37 to 77.81 nM and much less potent cytotoxicity against normal cells (IC50 > 10 μM). Mechanistically, it effectively inhibited cell proliferation and migration and induced the cell cycle arrest and apoptosis in a concentration-dependent manner. Besides, A3 possessed greatly improved pharmacokinetic properties including over 10-fold higher plasma exposure (AUC0-t: 541 vs 43.6 h∗ng/mL) and better oral bioavailability (F: 20.85 % vs 2.70 %), lower systemic plasma clearance (CL:1897 vs 24523 mL/h/kg), as well as longer half-life (T1/2: 0.530 vs 0.108 h) when compared to diphyllin. In a tumor cell xenograft model, A3 significantly suppressed the CAL27 tumor growth with a TGI of 42.2 % without obvious safety concern, which is superior to that of diphyllin (TGI = 23.3 %), suggesting great potential for treatment of HNSCC.

Ringing medicinal chemistry: The importance of 3-membered rings in drug discovery

Scaffold-based drug design has become increasingly prominent in the pharmaceutical field due to the systematic and effective approach through which it facilitates the development of novel drugs. The identification of key scaffolds provides medicinal chemists with a fundamental framework for subsequent research. With mounting evidence suggesting that increased aromaticity could impede the chances of developmental success for oral drug candidates, there is an imperative need for a more thorough exploration of alternative ring systems to mitigate attrition risks. The unique characteristics exhibited by three-membered rings have led to their application in medicinal chemistry. This review explores the use of cyclopropane-, aziridine-, thiirane-, and epoxide-containing compounds in drug discovery, focusing on their roles in approved medicines and drug candidates. Specifically, the importance of the three-membered ring systems in rending biological activity for each drug molecule was highlighted. The undeniable therapeutic value and intriguing features presented by these compounds suggest significant pharmacological potential, providing justification for their incorporation into the design of novel drug candidates.

Metal-free internal nucleophile-triggered domino route for synthesis of fused quinoxaline [1,4]-diazepine hybrids and the evaluation of their DNA binding properties

An unprecedented metal-free synthesis of fused quinoxaline 1,5-disubstituted-[1,4]-diazepine hybrids have been reported under mild conditions through a domino intermolecular SNAr followed by an internal nucleophile-triggered intramolecular SNAr pathway. Our strategy offers the flexibility for the introduction of a broad variety of functionalities at the N-1 position of fused diazepine moiety by using suitable diamine tails to design structurally diverse scaffolds. The DNA binding properties of representative quinoxaline diazepine hybrids were studied using UV-vis absorbance and EtBr displacement assay and were found to be governed by the functionalities at the N-1 position. Interestingly, compound 11f containing the N-1 benzyl substitution demonstrated significant DNA binding (KBH ∼ 2.15 ± 0.25 × 104 M-1 and Ksv ∼ 12.6 ± 1.41 × 103 M-1) accompanied by a bathochromic shift (Δλ ∼ 5 nm). In silico studies indicated possible binding of diazepine hybrid 11f at the GC-rich major groove in the ct-DNA hexamer duplex and showed comparable binding energies to that of ethidium bromide. The antiproliferative activity of compounds was observed in the given order in different cell lines: (HeLa > HT29 > SKOV 3 > HCT116 > HEK293). Lead compound 11f demonstrated maximum cytotoxicity (IC50 value of 13.30 μM) in HeLa cell lines and also caused early apoptosis-mediated cell death in cancer cell lines. We envision that our work will offer newer methodologies for the construction of fused quinoxaline 1,5-disubstituted-[1,4]-diazepine class of molecules.

Seven-membered N-heterocycles as approved drugs and promising leads in medicinal chemistry as well as the metal-free domino access to their scaffolds

Azepanes or azepines are structural motifs of many drugs, drug candidates and evaluated lead compounds. Even though compounds having N-heterocyclic 7-membered rings are often found in nature (e.g. alkaloids), the natural compounds of this group are rather rare as approved therapeutics. Thus, recently studied and approved azepane or azepine-congeners predominantly consist of semi-synthetically or synthetically-obtained scaffolds. In this review a comparison of approved drugs and recently investigated leads was proposed taking into regard their structural aspects (stereochemistry), biological activities, pharmacokinetic properties and confirmed molecular targets. The 7-membered N-heterocycles reveal a wide range of biological activities, not only against CNS diseases, but also as e.g. antibacterial, anticancer, antiviral, antiparasitic and against allergy agents. As most of the approved or investigated potential drugs or lead structures, belonging to 7-membered N-heterocycles, are synthetic scaffolds, this report also reveals different and efficient metal-free cascade approaches useful to synthesize both simple azepane or azepine-containing congeners and those of oligocyclic structures. Stereochemistry of azepane/azepine fused systems, in view of biological data and binding with the targets, is discussed. Apart from the approved drugs, we compare advances in SAR studies of 7-membered N-heterocycles (mainly from 2018 to 2023), whereas the related synthetic part concerning various domino strategies is focused on the last ten years.

Oxidative Cascade Iodocyclization of 1,n-Dienes: Synthesis of Iodinated Benzo[b]azepine and Benzo[b]azocine Derivatives

An oxidative cascade iodocyclization of 1,7- or 1,8-dienes has been realized under mild conditions. By employing I2 as an iodine source, this protocol provides a concise and efficient approach to a great deal of biologically significant iodinated benzo[b]azepine and benzo[b]azocine derivatives in moderate to good yields. The gram-scale synthesis and further transformation of products render the approach practical and attractive. Radical trapping and deuterium-labeling experiments help to understand the mechanism.

Development of diphenylmethylpiperazine hybrids of chloroquinoline and triazolopyrimidine using Petasis reaction as new cysteine proteases inhibitors for malaria therapeutics

Malaria is a widespread infectious disease, causing nearly 247 million cases in 2021. The absence of a broadly effective vaccine and rapidly decreasing effectiveness of most of the currently used antimalarials are the major challenges to malaria eradication efforts. To design and develop novel antimalarials, we synthesized a series of 4,7-dichloroquinoline and methyltriazolopyrimidine analogues using a multi-component Petasis reaction. The synthesized molecules (11-31) were screened for in-vitro antimalarial activity against drug-sensitive and drug-resistant strains of Plasmodium falciparum with an IC₅₀ value of 0.53 μM. The selected compounds were screened to evaluate in-vitro and in-silico enzyme inhibition efficacy against two cysteine proteases, PfFP2 and PfFP3. The compounds 15 and 17 inhibited PfFP2 with an IC₅₀ = 3.5 and 4.8 μM, respectively and PfFP3 with an IC₅₀ = 4.9 and 4.7 μM, respectively. Compounds 15 and 17 were found equipotent against the Pf3D7 strain with an IC₅₀ value of 0.74 μM, whereas both were displayed IC₅₀ values of 1.05 μM and 1.24 μM for the PfW2 strain, respectively. Investigation of effect of compounds on parasite development demonstrated that compounds were able to arrest the growth of the parasites at trophozoite stage. The selected compounds were screened for in-vitro cytotoxicity against mammalian lines and human red-blood-cell (RBC), which demonstrated no significant cytotoxicity associated with the molecules. In addition, in silico ADME prediction and physiochemical properties supported the drug-likeness of the synthesized molecules. Thus, the results highlighted the diphenylmethylpiperazine group cast on 4,7-dichloroquinoline and methyltriazolopyrimidine using Petasis reaction may serve as models for the development of new antimalarial agents.

Photophysical evaluation on the electronic properties of synthesized biologically significant pyrido fused imidazo[4,5-c]quinolines

A single pot microwave assisted method was employed to synthesize a series of novel pyrido fused imidazo[4,5-c]quinolines. The electronic properties of these derivatives were investigated by following their photophysical behaviour under isolated and solvated conditions via computational and experimental approaches. The solvatochromic effect of these derivatives was investigated in the ground and excited singlet states by following the absorption and fluorescence emission and excitation spectra. Further the effect of general and specific solvent effects were also investigated by plotting Stokes shift against Lippert-Mataga, ET(30) and Kamlet-Taft polarity parameters respectively. The deviation from linearity in ET(30) plot indicates that formation of different species in polar protic solvents. The biological applications of these derivatives as potential drug candidates were evaluated by in silico computational methods followed by pharmacokinetic properties predictions. The ability of these derivatives to inhibit human casein kinase 2 (CK2) was evaluated. The structure activity relationships were correlated by evaluating the electronic properties through experimental photophysical investigations including solvatochromic effect and computational electronic structure calculations. Of the various derivatives, p-nitro phenyl substituted pyrido fused imidazo[4,5-c]quinoline exhibited good inhibitory activity against CK2 enzyme and hence could serve as a promising drug candidate.

Synthesis of new benzimidazole derivatives containing 1,3,4-thiadiazole: their in vitro antimicrobial, in silico molecular docking and molecular dynamic simulations studies

A series of some new benzimidazole-1,3,4-thiadiazoles was synthesized. The structures of target substances were confirmed by using ¹H-NMR and ¹³С-NMR spectroscopy, mass spectrometry and elemental analysis. The synthesized compounds were evaluated for antimicrobial activity against six bacterial strains namely Escherichia coli (ATCC 25922), Klebsiella pneumoniae (ATCC 13883), Pseudomonas aeruginosa (ATCC 27853), Enterococcus faecalis (ATCC 2942), Bacillus subtilis (ATCC 6633), Staphylococcus aureus (ATCC 29213)and four fungal strains namely Candida albicans (ATCC 24433), Candida krusei (ATCC 6258), Candida parapsilosis (ATCC 22019) and Candida glabrata (ATCC 9). Antimicrobial data revealed that compounds 4f and 4i with MIC of < 0.97 µg/mL were found to be most effective against E. coli. Among the studied molecules, compounds 4f and 4i showed the best antifungal activity with MIC value of 1.95 µg/mL. Additionally, docking studies were performed towards the most promising compounds 4f and 4i, in the active site of DNA gyrase revealing strong interactions. A molecular dynamics (MD) simulation analysis was also used to investigate the dynamic nature, binding interaction, and protein-ligand stability.

Iodo-sulphonylation of 1,6-enynones: a metal-free strategy to synthesize N-substituted succinimides

An iodine-mediated radical cyclization of 1,6-enynones with sulphonyl hydrazides using tert-butyl hydroperoxide (TBHP) as the oxidant has been developed for the synthesis of iodo-sulphonylated-succinimide derivatives. The notable advantages of the developed method are metal-free conditions, broad functional group tolerance, column chromatography-free purification, high stereoselectivity (E isomer), shorter reaction times, and the cascade construction of three new bonds (C-S, C-I, and C-C). The synthetic application of the iodo-functionality has been extended to the Heck coupling reaction with acrylonitrile and to the Suzuki coupling reaction with benzene boronic acid.