Effects of substitution and conjugation on ESIPT behavior of Schiff base derivatives

The excited-state proton transfer (ESIPT) behavior of organic fluorophores has been of great interest due to their unique photophysical properties. In this work, we have focused on the excited state kinetic behavior of four Schiff base organic molecules (i.e. CPMP, CPMMP, CPMDP, and CPMN) in acetonitrile solvents. The electron-donating of substituents and conjugation effects on the photophysical properties and ESIPT process of the Schiff base derivatives are investigated by theoretical methods. The results show that the hydrogen bonds are all enhanced in the excited states, which could provide the impetus for the ESIPT process. To further reveal the reaction process of ESIPT, we have scanned the potential energy curves of the ESIPT process and compared the potential barriers. It is found that the stronger the substituents give electrons and the conjugation effects the more favorable the excited state proton transfer (ESIPT). In the meantime, this study paves the way for the development of new Schiff base materials based on ESIPT.

Antimicrobial and antibiofilm activities of Cu(II) Schiff base complexes against methicillin-susceptible and resistant Staphylococcus aureus

Background

Methicillin-resistance S. aureus (MRSA) possesses the ability to resist multiple antibiotics and form biofilm. Currently, vancomycin remains the last drug of choice for treatment of MRSA infection. The emergence of vancomycin-resistant S. aureus (VRSA) has necessitated the development of new therapeutic agents against MRSA. In this study, the antimicrobial and antibiofilm activities of two copper-complexes derived from Schiff base (SBDs) were tested individually, and in combination with oxacillin (OXA) and vancomycin (VAN) against reference strains methicillin-susceptible and methicillin-resistant Staphylococcus aureus. The toxicity of the SBDs was also evaluated on a non-cancerous mammalian cell line.

Methods

The antimicrobial activity was tested against the planktonic S. aureus cells using the microdilution broth assay, while the antibiofilm activity were evaluated using the crystal violet and resazurin assays. The cytotoxicity of the SBDs was assessed on MRC5 (normal lung tissue), using the MTT assay.

Results

The individual SBDs showed significant reduction of biomass and metabolic activity in both S. aureus strains. Combinations of the SBDs with OXA and VAN were mainly additive against the planktonic cells and cells in the biofilm. Both the compounds showed moderate toxicity against the MRC5 cell line. The selectivity index suggested that the compounds were more cytotoxic to S. aureus than the normal cells.

Conclusion

Both the SBD compounds demonstrated promising antimicrobial and antibiofilm activities and have the potential to be further developed as an antimicrobial agent against infections caused by MRSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00473-4.

Synthesis, anticancer evaluation and molecular docking studies of methotrexate's novel Schiff base derivatives against malignant glioma cell lines

Recent years have witnessed advancement in cancer research that has led to the development of improved cytotoxic therapies with reduced side effects. Methotrexate (MTX) is a commonly used anticancer drug having robust activity, but with serious side effects. Several derivatives of MTX have been reported by modification at different sites to reduce its side effects and enhance efficacy. The current work describes the development of active MTX Schiff base derivatives by treating MTX with several aldehydes viz 2-chlorobenzaldehyde, 3-nitrobenzaldehyde, 5-chloro-2-hydroxybenz-aldehyde, 2-hydroxy-5-nitrobenzaldehyde, 2-thiocarboxyaldehyde, trans-2-pentenal and glutaraldehyde. Newly synthesized derivatives were evaluated for their anticancer potential against human malignant glioma U87 (MG-U87) cell lines at different concentrations of 200 μM, 100 μM, 50 μM, 25 μM, 12.5 μm, 6.25 μm and 0 μM. MTX derivatives with 2-Chlorobenzaldehyde (IC₅₀ ∼100 μM), 2-Thiocarboxyaldehyde (IC₅₀ <200 μM) and 2- Pentenal (IC₅₀ ∼250 μM) showed much better activity at 100 µM compared to 400 µM concentration of MTX. Molecular docking studies were performed that showed a good correlation with the results obtained from in vitro experiments. The excellent agreement between molecular modeling and growth inhibition assay shows that the binding mode hypothesis is justly close to the experimentally biological values, therefore, may prove helpful for further lead optimization and clinical trials.Communicated by Ramaswamy H. Sarma.

Data on synthesis and characterization of new p-nitro stilbene Schiff bases derivatives as an electrochemical DNA potential spacer

The structural investigation of synthesized compounds can be carried out by various spectroscopic techniques. It is an important prospect in order to elucidate the structure of the desired products before being further utilized. The preparation of new p-nitro stilbene Schiff base derivatives as an electrochemical DNA potential spacer was synthesized using (E)-4-(4-nitrostyryl)aniline from Heck reaction with aldehydes in ethanolic solution. The data presented here in this article contains FTIR, UV-Vis and ¹H and ¹³C NMR of (E)-4-(4-nitrostyryl)aniline and nitrostyryl aniline derivatives.

Synthesis, structure-activity relationships and preliminary mechanism study of N-benzylideneaniline derivatives as potential TLR2 inhibitors

Toll-like receptor 2 (TLR2) can recognize pathogen-associated molecular patterns to defense against invading organisms and has been represents an attractive therapeutic target. Until today, none TLR2 small molecule antagonist have been developed in clinical trial. Herein, we designed and synthesized 50 N-benzylideneaniline compounds with the help of CADD. And subsequent in vitro studies leading to the optimized compound SMU-A0B13 with most potent inhibitory activity to TLR2 (IC₅₀=18.21 ± 0.87 μM). Preliminary mechanism studies indicated that this TLR2 inhibitor can work through the NF-κB signaling pathway with high specificity and low toxicity, and can also efficiently downregulate inflammatory cytokines, such as SEAP, TNF-α and NO in HEK-Blue hTLR2, human PBMC and Raw 264.7 cell lines. Additionally, the docking situation also indicate SMU-A0B13 can well bind to the TLR2-TIR (PDB: 1FYW) active domain, which probably explains the bioactivity.

Development of SECheM Concept for Isolation and Chemical Modification of Gossypol Directly from Cienfuegosia digitata

INTRODUCTION

Gossypol is an axially chiral natural polyphenol classically extracted from the Malavaceae family. Nevertheless, its extraction and isolation from a plant can be quite complicated and extremely time-consuming since gossypol is known to be sensitive to degradation under solvents, high temperature and light action. Moreover, its purification over column chromatography is a challenging problem due to its ability to oxidise and the existence of various tautomer forms.

OBJECTIVE

To develop an efficient "one-step" strategy for simultaneous extraction and semi-synthesis by short-circuiting critical gossypol isolation and purification steps.

METHODOLOGY

Gossypol was first isolated from Cienfuegosia digitata roots, characterised (by 1D and 2D NMR) and quantified (by UV spectrophotometry). Thus, aniline was selected to test the "one-step" in situ trapping of freshly extracted gossypol leading to a Schiff base analogue. After screening solvents and extraction times on this model reaction, the "SECheM" (simultaneous extraction and chemical modification) concept was successfully extended to other amines, underlining the efficiency and the robustness of the strategy.

RESULTS

After having shown that gossypol occurred as a major compound in C. digitata roots, different experimental procedures using Soxhlet extraction in the presence of aniline pointed out the best conditions for the SECheM concept (7 h of reaction and extraction time in ether as solvent). Ultimately, the concept has been generalised to 17 other amines.

CONCLUSION

This is a report of the first semi-synthesis that allows: (1) "in situ" preparation of more stable gossypol Schiff base derivatives directly from ground plant material and (2) circumvention of gossypol extraction and purification problems. Copyright © 2017 John Wiley & Sons, Ltd.

Crystal structures of the Schiff base derivatives (E)-N'-[(1H-indol-3-yl)methyl-idene]isonicotino-hydrazide ethanol monosolvate and (E)-N-methyl-2-[1-(2-oxo-2H-chromen-3-yl)ethyl-idene]hydrazinecarbo-thio-amide

The crystal structures of two title Schiff base derivatives, C15H12N4O·C2H6O (1·EtOH) and C13H13N3O2S (2), were determined at 110 and 100 K, respectively. In the crystal of compound 1·EtOH, the (E)-N'-[(1H-indol-3-yl)methyl-idene]isonicotinohydrazide and ethanol mol-ecules are linked by O-H⋯O, N-H⋯O and N-H⋯N hydrogen bonds, forming a tape structure running along the b-axis direction. The tapes are weakly linked via a C-H⋯N inter-action. In the crystal of compound 2, (E)-N-methyl-2-[1-(2-oxo-2H-chromen-3-yl)ethyl-idene]hydrazinecarbo-thio-amide mol-ecules are linked via N-H⋯O and C-H⋯O hydrogen bonds, forming a helical chain along the b-axis direction. The chains are further linked into a layer expanding parallel to (102) through C-H⋯S inter-actions.

Synthesis and Herbicidal Activities of p-Menth-3-en-1-amine and Its Schiff Base Derivatives

p-Menth-3-en-1-amine, 4, and its Schiff base derivatives, 5a-l, were designed and synthesized. They were characterized by FT-IR, ESI⁺-MS, HRMS, ¹H NMR, and ¹³C NMR spectral analyses, and their pre-emergence herbicidal activities against ryegrass were evaluated. All of the compounds showed excellent herbicidal activity. The Schiff bases showed stronger herbicidal activities than the original amine 4. These compounds showed herbicidal activities comparable to that of glyphosate. The herbicidal activities of 5k and 5l against ryegrass shoot growth were 78.3 and 355.6% higher than that of glyphosate, respectively. Furthermore, the introduction of a chlorine or bromine atom into the Schiff base derivatives containing a furan or benzene ring was beneficial to increase the activity. However, the herbicidal activities were not clearly affected when the heteroatom of the five-membered heterocyclic Schiff base or the position of the substituent on pyridine Schiff base was altered.