Synthesis, spectroscopic, SC-XRD/DFT and non-linear optical (NLO) properties of chromene derivatives

In the present study, we reported the efficient synthesis of novel, heterocyclic, coumarin-based pyrano-chromene derivatives, 2-amino-8-methyl-5-oxo-4-[2-(2-oxo-2H-chromen-3-ylmethoxy)-phenyl]-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile (4a) and 2-amino-8-methyl-5-oxo-4-[2-(2-oxo-2H-chromen-3-ylmethoxy)-phenyl]-4H,5H-pyrano[3,2-c]chromene-3-carboxylic acid methyl ester (4b). The chemical structures of synthesized compounds were resolved by employing various spectroscopic techniques like UV-Vis, FT-IR, ¹H & ¹³C NMR, and single crystal X-ray diffraction (SC-XRD) analysis. The compounds; 4a and 4b, with appealing π-bonded skeleton were further analyzed in terms of their electronic and structural aspects using an integral approach of density functional theory (DFT) and time-dependent DFT (TD/DFT). The methodology: M06-2X/6-31G(d,p) level of theory was applied to compare their experimental data with theoretical outcomes using quantum chemical analysis. The frontier molecular orbitals (FMOs) study revealed that, 4a possesses a low band gap (5.168 eV) as compared to 4b (6.308 eV). Global reactivity parameters were associated with E _gap values as 4a, with the lowest band gap showed the smaller value of hardness (0.094 eV) and a larger value of softness (5.266 eV). The non-linear optical (NLO) insight exhibited that, the average polarizability 〈α〉 and second hyperpolarizability (γ _tot) were observed in 4a as 6.77005 × 10^-23 and 0.145 × 10⁴ esu, respectively. Overall, the computational studies suggest that the investigated compounds have distinct NLO properties.

Molecular duplexes featuring NH···N, CH···O and CH···π interactions in solid-state self-assembly of triazine-based compounds

Synthetic supramolecular structures constructed through the cooperative action of numerous non-covalent forces are highly desirable as models to unravel and understand the complexity of systems created in nature via self-assembly. Taking advantage of the low cost of 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride) and the sequential nucleophilic substitution reactions with almost all types of nucleophiles, a series of six structurally related novel s-triazine derivatives 1-6 were synthesized and structurally characterized based on their physical, spectral and crystallographic data. The solid-state structures of all the six compounds showed intriguing and unique molecular duplexes featuring NH···N, CH···O and CH···π interactions. Careful analysis of different geometric parameters of the involved H-bonds indicates that they are linear, significant and are therefore responsible for guiding the three-dimensional structure of these compounds in the solid state. The prevalence of sextuple hydrogen bond array-driven molecular duplexes and the possibility of structural modifications on the s-triazine ring render these novel triazine derivatives 1-6 attractive as a platform to create heteroduplex constructs and their subsequent utility in the field of supramolecular chemistry and crystal engineering.

Development, Molecular Docking, and In Silico ADME Evaluation of Selective ALR2 Inhibitors for the Treatment of Diabetic Complications via Suppression of the Polyol Pathway

Diabetic complications are associated with overexpression of aldose reductase, an enzyme that catalyzes the first step of the polyol pathway. Osmotic stress in the hyperglycemic state is linked with the intracellular accumulation of sorbitol along with the depletion of NADPH and eventually leads to oxidative stress via formation of reactive oxygen species and advanced glycation end products (AGEs). These kinds of mechanisms cause the development of various diabetic complications including neuropathy, nephropathy, retinopathy, and atherosclerotic plaque formation. Various aldose reductase inhibitors have been developed to date for the treatment of diabetic complications, but all have failed in different stages of clinical trials due to toxicity and poor pharmacokinetic profiles. This toxicity is rooted in a nonselective inhibition of both ALR2 and ALR1, homologous enzymes involved in the metabolism of toxic aldehydes such as methylglyoxal and 3-oxyglucosazone. In the present study, we developed a series of thiosemicarbazone derivatives as selective inhibitors of ALR2 with both antioxidant and antiglycation potential. Among the synthesized compounds, 3c exhibited strong and selective inhibition of ALR2 (IC₅₀ 1.42 μM) along with good antioxidant and antiglycative properties. The binding mode of 3c was assessed through molecular docking and cluster analysis via MD simulations, while in silico ADME evaluation studies predicted the compounds' druglike properties. Therefore, we report 3c as a drug candidate with promising antioxidant and antiglycative properties that may be useful for the treatment of diabetic complications through selective inhibition of ALR2.

Synthesis, solid state self-assembly driven by antiparallel π⋯π stacking and {⋯H-C-C-F}2 dimer synthons, and in vitro acetyl cholinesterase inhibition activity of phenoxy pendant isatins

A series of novel phenoxy pendant isatins PI1-12 have been synthesized in excellent yields by a simple nucleophilic substitution reaction involving isatins and 1-(2-bromoethoxy)-4-substituted benzenes, and characterized by their FT-IR, ¹H NMR, ¹³C NMR and GC-MS data, and in the case of PI4 by its single crystal X-ray analysis. The solid-state structure of PI4 showed an intriguing and unique 1D-supramolecular chain-based self-assembled structure, the driving force of which is mainly the strong antiparallel π⋯π stacking and {⋯H-C-C-F}₂ dimer synthons. This compound not only highlights the potential of the isatin moiety in forming strong antiparallel π⋯π stacking interactions but also provides a platform to have considerable insight into the nature, strength and directionality of much debated π-π and C-H⋯F-C interactions. The in vitro biological studies revealed that three phenoxy pendant isatins PI1, PI2 and PI4 are highly potent inhibitors of acetylcholinesterase enzyme with IC₅₀ values of 0.52 ± 0.073 μg ml^-1, 0.72 ± 0.012 μg ml^-1 and 0.68 ± 0.011 μg ml^-1, respectively, showing comparable activity to the standard drug, donepezil (IC₅₀ = 0.73 ± 0.015 μg ml^-1). A simple and efficient synthesis of phenoxy pendant isatins PI1-12 from inexpensive and commercially available starting materials, and their high potential of acetyl cholinesterase inhibition provide an attractive opportunity to find more effective medication for Alzheimer's disease (AD).

Phenoxy pendant isatins as potent α-glucosidase inhibitors: reciprocal carbonyl⋯carbonyl interactions, antiparallel π⋯π stacking driven solid state self-assembly and biological evaluation

Carbonyl–carbonyl (CO⋯CO) interactions are recently explored noncovalent interactions of significant interest owing to their role in the stability of biomacromolecules. Currently, substantial efforts are being made to understand the nature of these interactions. In this study, twelve phenoxy pendant isatins 1–12 have been evaluated for their α-glucosidase inhibitory potential in addition to the analysis of X-ray single crystals of 4 and 9. Both compounds 4 and 9 showed intriguing and unique self-assembled structures. The CO⋯CO and antiparallel displaced π⋯π stacking interactions are mainly involved in the formation of 1D-stair like supramolecular chains of 4 whereas antiparallel π⋯π stacking interactions drive the formation of 1D-columnar stacks of 9. These compounds not only highlight the potential of the isatin moiety in forming strong CO⋯CO and antiparallel π⋯π stacking interactions but also are interesting models to provide considerable insight into the nature of these interactions. The in vitro biological studies revealed that all twelve phenoxy pendant isatins 1–12 are highly potent inhibitors of α-glucosidase enzyme with IC₅₀ values ranging from 5.32 ± 0.17 to 150.13 ± 0.62 μM, showing many fold more potent activity than the standard drug, acarbose (IC₅₀ = 873.34 ± 1.67). Easy access and high α-glucosidase inhibition potential of these phenoxy pendant isatins 1–12 provide an attractive platform for finding more effective medication for controlling postprandial hyperglycemia.

Carbonyl–carbonyl (CO⋯CO) interactions are recently explored noncovalent interactions of significant interest owing to their role in the stability of biomacromolecules.

Exploration of Chromone-Based Thiosemicarbazone Derivatives: SC-XRD/DFT, Spectral (IR, UV-Vis) Characterization, and Quantum Chemical Analysis

By the condensation of thiosemicarbazide with coumarin aldehyde, two novel substituted thiosemicarbazones with chemical formulae C24H25N3O3S (3a) and C26H23N3O3S (3b) have been synthesized. The synthesized compounds were resolved using SC-XRD, and structure elucidation was carried out using 1H NMR, 13C NMR, UV-visible, and FT-IR spectroscopic analyses. Computational calculations at the B3LYP/6-311+G(d,p) level of theory were performed to countercheck the experimental (UV-vis, FT-IR) findings and explore the electronic (FMO, NBO, MEP) properties of 3a-b. The nonlinear optical (NLO) properties of 3a-b were estimated using B3LYP, HF, LC-BLYP, CAM-B3LYP, M062X, and M06 functionals in combination with the 6-311+G(d,p) basis set. The crystallographic data revealed that compounds were crystallized as an orthorhombic crystal lattice with the Pbcn space group and the triclinic crystal lattice with the P̅1 space group. A good concurrence among experimental SC-XRD-generated bond lengths, bond angles, FT-IR, UV-vis, and corresponding DFT results was found, which confirms the purity of both compounds. The NBO analysis confirmed the presence of intramolecular hydrogen bonding and hyperconjugative interactions, which not only were the pivotal cause of stability of the investigated compounds but also led to an overwhelming NLO response. The energy differences calculated for HOMO/LUMO are 3.053 and 3.118 eV in 3a and 3b, respectively. The crystal 3b showed a higher value of first-order polarizability at all levels of theory than 3a. Overall results show that the crystals under investigation are polarized in nature with a good dipole moment. A comparative analysis with urea molecules clearly indicates that the studied compounds are acceptable NLO candidates and they can be used for future technological applications.

Intramolecular Noncovalent Carbon Bonding Interaction Stabilizes the cis Conformation in Acylhydrazones

Noncovalent carbon bonding, a recently explored σ-hole interaction, was hitherto supposed to be a weak and structure-guided interaction. Here, its role in the intramolecular stabilization of the cis conformation of the amide moiety in acylhydrazones is described. The calculations reveal an electron donation from the lone pair of the nitrogen atom to the empty antibonding C-N orbital [LP(N)→BD*(C-N)] with a concomitant stabilization energy of E⁽²⁾ =1.2 kcal mol^-1 .

Synthesis, crystal structure, molecular docking studies and bio-evaluation of some N4-benzyl-substituted isatin- 3-thiosemicarbazones as urease and glycation inhibitors

Fifteen N4-benzyl-substituted isatin-3-thiosemicarbazones 5a–o were synthesized and evaluated for their urease and glycation inhibitory potential. Lemna aequinocitalis growth and Artemia salina assays were also done to determine their phytotoxic and toxic effects. All compounds are potent inhibitors of the urease enzyme, displaying inhibition [half maximal inhibitory concentration (IC50)=1.08±0.12–11.23±0.19 μm] superior to that of the reference inhibitor thiourea (IC50=22.3±1.12 μm). Compounds 5c, 5d, 5h, 5j,k are potent antiglycating agents, showing glycation inhibitory activity better than that of the reference inhibitor rutin (IC50 values 209.87±0.37–231.70±6.71 vs. 294.5±1.5 μm). In the phytotoxicity assay, 11 thiosemicarbazones 5a–d, 5g, 5h, 5j–l, 5n,o are active, demonstrating 5–100% growth inhibition of L. aequinocitalis at the highest tested concentrations (1000 or 500 μg/mL). In the brine shrimp (A. salina) lethality bioassay, three derivatives 5b, 5j and 5o are active with median lethal dose (LD50) values of 3.63×10−5, 2.90×10−5 and 2.31×10−4 m, respectively.

Coumarin-based thiosemicarbazones as potent urease inhibitors: synthesis, solid state self-assembly and molecular docking

A series of coumarin-based thiosemicarbazones and their metal complexes have been synthesized and their in vitro potency against urease was evaluated.

Me3N-promoted synthesis of 2,3,4,4a-tetrahydroxanthen-1-one: preparation of thiosemicarbazone derivatives, their solid state self-assembly and antimicrobial properties

Thiosemicarbazones (5a–5j) have been synthesized from 2,3,4,4a-tetrahydroxanthen-1-one, obtained in high yield through Me₃N-promoted domino Baylis–Hillman/oxa-Michael reaction. Their solid-state self-assembly and antimicrobial properties are studied.

Structure-fluorescence relationship: interplay of non-covalent interactions in homologous 1,3,5-triaryl-2-pyrazolines

A series of new homologous 1,3,5-triaryl-2-pyrazolines have been synthesized to understand the interplay of non-covalent interactions in the context of a structure-fluorescence relationship.

Robustness of a thioamide {⋯H–N–CS}2 synthon: synthesis and the effect of substituents on the formation of layered to cage-like supramolecular networks in coumarin–thiosemicarbazone hybrids

The study has been carried out to highlight the potential of thiosemicarbazones in crystal engineering.