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14 pages, 2707 KiB  
Article
Understanding Bio-Orthogonal Strain-Driven Sydnone Cycloadditions: Data-Assisted Profiles and the Search for Linear Relationships
by Juan García de la Concepción, Pedro Cintas and Rafael Fernando Martínez
Molecules 2025, 30(13), 2770; https://doi.org/10.3390/molecules30132770 - 27 Jun 2025
Viewed by 355
Abstract
In the realm of click-type reactions and their application to bioorthogonal chemistry in living organisms, metal-free [3+2] cycloadditions involving mesoionic rings and strained cycloalkynes have gained increasing attention and potentiality in recent years. While there has been a significant accretion of experimental data, [...] Read more.
In the realm of click-type reactions and their application to bioorthogonal chemistry in living organisms, metal-free [3+2] cycloadditions involving mesoionic rings and strained cycloalkynes have gained increasing attention and potentiality in recent years. While there has been a significant accretion of experimental data, biological assays, and assessments of reaction mechanisms, some pieces of the tale are still missing. For instance, which structural and/or stereoelectronic effects are actually interlocked and which remain unplugged. With the advent of data-driven methods, including machine learning simulations, quantitative estimations of relevant observables and their correlations will explore better the chemical space of these transformations. Here we unveil a series of linear relationships, such as Hammett-type correlations, as well as deviations of linearity, using the case study of phenylsydnone (and its 4-aryl-substituted derivatives) with a highly reactive bicyclo[6.1.0]nonyne carbinol. Through accurate estimation of activation barriers and prediction of rate constants, our findings further increase the significance of integrating strain release and electronic effects in organic reactivity. Moreover, such results could pave the way to use mesoionics cycloadditions as probes for measuring the extent of delocalization-assisted strain release, which can be applied to related reactions involving dipoles and strained rings. Full article
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12 pages, 1408 KiB  
Communication
Synthesis of Mesoionic 1,3,4-Thiadiazole-2-Thiolates
by Sean Ray Kahnert and Andreas Schmidt
Molbank 2025, 2025(2), M2010; https://doi.org/10.3390/M2010 - 22 May 2025
Viewed by 803
Abstract
A reliable synthesis of C5-unsubstituted 1,3,4-thiadiazole-2-thiolates is described that avoids potentially explosive or laborious steps. This work presents a reliable method for preparing the starting material dithioformate from carbon disulfide and potassium or sodium tri-sec-butylhydroborates for the preparation of the mesoionic [...] Read more.
A reliable synthesis of C5-unsubstituted 1,3,4-thiadiazole-2-thiolates is described that avoids potentially explosive or laborious steps. This work presents a reliable method for preparing the starting material dithioformate from carbon disulfide and potassium or sodium tri-sec-butylhydroborates for the preparation of the mesoionic title compounds with potassium hydrazinecarbodithioates. New 1,3,4-thiadiazole-2-thiolates are presented, and missing structural analysis data of known derivatives are added (1D- and 2D-NMR, HR-ESI-MS, IR). Full article
(This article belongs to the Section Organic Synthesis and Biosynthesis)
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5 pages, 1538 KiB  
Communication
Synthesis and Characterization of N-Nitroso-3-morpholinosydnonimine as NO Radical Donor
by Nathalie Saffon-Merceron, Christian Lherbet and Pascal Hoffmann
Molbank 2024, 2024(4), M1886; https://doi.org/10.3390/M1886 - 24 Sep 2024
Cited by 1 | Viewed by 1113
Abstract
N-Nitroso-3-morpholinosydnonimine 3 was prepared by nitrosation of SIN-1 and characterized by 1H-NMR, 13C-NMR, and HRMS. Its structure, confirmed by single crystal X-ray diffraction analysis, was found to be in agreement with its mesoionic and aromatic character. Unlike 3-morpholino-sydnonimine (SIN-1), which [...] Read more.
N-Nitroso-3-morpholinosydnonimine 3 was prepared by nitrosation of SIN-1 and characterized by 1H-NMR, 13C-NMR, and HRMS. Its structure, confirmed by single crystal X-ray diffraction analysis, was found to be in agreement with its mesoionic and aromatic character. Unlike 3-morpholino-sydnonimine (SIN-1), which releases both nitric oxide and superoxide radical, decomposition of this nitrosylated sydonimine could yield nitric oxide as the only decomposition product, and thus without the formation of toxic peroxynitrite. Full article
(This article belongs to the Section Organic Synthesis and Biosynthesis)
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15 pages, 5560 KiB  
Review
Bioorthogonal “Click” Cycloadditions: A Toolkit for Modulating Polymers and Nanostructures in Living Systems
by Irene Lepori, Yavuz Oz, Jungkyun Im, Nandan Ghosh, Mohuya Paul, Ulrich S. Schubert and Stefano Fedeli
Reactions 2024, 5(1), 231-245; https://doi.org/10.3390/reactions5010010 - 4 Mar 2024
Cited by 5 | Viewed by 3173
Abstract
“Click” cycloadditions offer effective pathways for the modifications of supramolecular structures, polymers, and nanomaterials. These reactions include bioorthogonal mechanisms that do not interfere with the biological processes, providing a type of chemistry to operate directly in living environments, such as cells and animals. [...] Read more.
“Click” cycloadditions offer effective pathways for the modifications of supramolecular structures, polymers, and nanomaterials. These reactions include bioorthogonal mechanisms that do not interfere with the biological processes, providing a type of chemistry to operate directly in living environments, such as cells and animals. As a result, the “click” cycloadditions represent highly and selective tools for tailoring the properties of nanomedicine scaffolds, expanding the efficacy of multiple therapeutic strategies. We focused this minireview on the bioorthogonal cycloadditions, presenting an insight into the strategies to modify nanostructured biomedical scaffolds inside living systems. We organized the contributions according to the three main mechanisms of “click” cycloadditions: strain-promoted sydnone-alkyne, tetrazine ligation, and strain-promoted [3+2] azido-alkyne. Full article
(This article belongs to the Special Issue Cycloaddition Reactions at the Beginning of the Third Millennium)
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22 pages, 3633 KiB  
Review
Sydnone Imines as a New Class of Promising Plant Growth and Stress Tolerance Modulators—A First Experimental Structure–Activity Overview
by Maria Cherevatskaya, Ilia Cherepanov, Natalia Kalganova, Natalia Erofeeva, Ekaterina Romanovskaya, Andrej Frolov, Tatiana Bilova, Sergey Moiseev and Ludger A. Wessjohann
Stresses 2024, 4(1), 133-154; https://doi.org/10.3390/stresses4010008 - 16 Jan 2024
Cited by 3 | Viewed by 2261
Abstract
Due to the oncoming climate changes, various environmental stresses (drought, salinity, heavy-metals, low or high temperatures, etc.) might dramatically affect crop yields and the quality of produced foods. Therefore, to meet the growing food demand of the human population, improvement of stress tolerance [...] Read more.
Due to the oncoming climate changes, various environmental stresses (drought, salinity, heavy-metals, low or high temperatures, etc.) might dramatically affect crop yields and the quality of produced foods. Therefore, to meet the growing food demand of the human population, improvement of stress tolerance of the currently cultured crops is required. The knowledge of the molecular underlying mechanisms provides a versatile instrument to correct plant metabolism via chemical tools and to thereby increase their adaptive potential. This will preserve crop productivity and quality under abiotic stress conditions. Endogenously produced nitric oxide (NO) is one of the key signaling factors activating stress tolerance mechanisms in plants. Thus, the application of synthetic NO donors as stress-protective phytoeffectors might support maintaining plant growth and productivity under stressful conditions. Sydnone imines (sydnonimines) are a class of clinically established mesoionic heterocyclic NO donors which represent a promising candidate group for such phytoeffectors. Therefore, here, we provide an overview of the current progress in the application of sydnone imines as exogenous NO donors in plants, with a special emphasis on their potential as herbicides as well as herbicide antidotes, growth stimulants and stress protectors triggering plant tolerance mechanisms. We specifically address the structure–activity relationships in the context of the growth modulating activity of sydnone imines. Growth stimulating or antidote effects are typical for 4-α-hydroxybenzyl derivatives of sydnone imines containing an alkyl substituent in position N-3. The nature of the substituent of the N-6 atom has a significant influence on the activity profile and the intensity of the effect. Nevertheless, further investigations are necessary to establish reliable structure–activity relationships (SAR). Consequently, sydnone imines might be considered promising phytoeffector candidates, which are expected to exert either protective effects on plants growing under unfavorable conditions, or herbicidal ones, depending on the exact structure. Full article
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17 pages, 945 KiB  
Article
Sydnone Imines: A Novel Class of Plant Growth Regulators
by Alexander S. Lukatkin, Anastasia S. Sokolova, Andrey A. Lukatkin, Ilya A. Cherepanov, Natalia V. Kalganova and Sergey K. Moiseev
Agrochemicals 2023, 2(2), 203-219; https://doi.org/10.3390/agrochemicals2020015 - 18 May 2023
Cited by 1 | Viewed by 2081
Abstract
An increase in the yield of the main cereal crops in the context of global climate changes requires additional impacts on plants. Natural and synthetic plant growth regulators (PGRs) are used to increase plant productivity and reduce the injury level caused by abiotic [...] Read more.
An increase in the yield of the main cereal crops in the context of global climate changes requires additional impacts on plants. Natural and synthetic plant growth regulators (PGRs) are used to increase plant productivity and reduce the injury level caused by abiotic stressors. There is a growing need for novel highly effective plant growth stimulants to exhibit their effects at low doses and to not pose an environmental threat or injury to the crop quality. The derivatives of sydnone imine (SI), a mesoionic heterocycle possessing a 1,2,3-oxadiazole core, have been used as medicines until now but have not been used for agricultural applications. Some SI derivatives have recently been found to exhibit PGR properties. Herein, we report on the study of the PGR potential of nine SI derivatives bearing variable substituents at N(3), C(4), and N6 positions of the heterocycle designed to disclose the “molecular structure-PGR activity” relationship in this family. The SI derivatives were used in a wide concentration range (10−9–10−4 mol/L) for a pre-sowing treatment of winter wheat (Triticum aestivum L., two cultivars) and maize (Zea mays L., two hybrids) seeds in germinating experiments. All compounds were found to affect the growth of the axial organs of germinants, with the growth-stimulating or -inhibitory effect as well as its rate being considerably different for wheat and maize and, in many cases, also for roots and shoots. In addition, a pronounced concentration dependence of the effect was disclosed for many cases. The features of the molecular structure of SIs affecting their growth-regulating properties were elucidated. Compounds 4, 6, 7, and 8, which had exhibited a growth-promoting effect in germinating experiments, were used at appropriate concentrations for pot experiments on the same crops. For all compounds, the experiments showed a stimulating effect on the growth of roots (up to 80%), shoots (up to 112%), leaf area (up to 113%), fresh weights of roots (up to 83%), and aerial parts of the plants (up to 87%) or only on some of these parameters. The obtained results show a healthy outlook for the use of SI derivatives as promoting agents for improving the growth of cereal crop plants. Full article
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4 pages, 506 KiB  
Proceeding Paper
Synthesis of N-Heterocyclic Carbene Gold Complexes Using 2,4,6-Trimethylphenyl Sydnone as Model Substrate
by Diana E. Vita, Mercedes A. Badajoz, Marcos J. Lo Fiego and Gustavo F. Silbestri
Chem. Proc. 2022, 12(1), 14; https://doi.org/10.3390/ecsoc-26-13674 - 17 Nov 2022
Viewed by 1423
Abstract
Two gold(I) complexes have been synthesized by a two-step reaction. The first reaction step was the deprotonation with butyllithium to obtain the corresponding NHC. In the second reaction step, the metal precursor was added to afford the corresponding gold complex. At this point, [...] Read more.
Two gold(I) complexes have been synthesized by a two-step reaction. The first reaction step was the deprotonation with butyllithium to obtain the corresponding NHC. In the second reaction step, the metal precursor was added to afford the corresponding gold complex. At this point, the complex obtained depends on the nature of the metal precursor. A monocarbene complex (sydnone-Au-tht) was obtained using [Au(tht)Cl] as the metal precursor and a biscarbene complex (sydnone-Au-imidazolium) was obtained using a gold imidazolium complex as the metal precursor instead. The 13C-NMR resonance frequencies of the carbene carbon atom shifted to higher values from 97.3 to 135.6–139.7 ppm, mono and biscarbene, respectively. Full article
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27 pages, 8893 KiB  
Review
Recent Advances in the Synthesis and Biomedical Applications of Heterocyclic NO-Donors
by Leonid L. Fershtat and Egor S. Zhilin
Molecules 2021, 26(18), 5705; https://doi.org/10.3390/molecules26185705 - 21 Sep 2021
Cited by 28 | Viewed by 4479
Abstract
Nitric oxide (NO) is a key signaling molecule that acts in various physiological processes such as cellular metabolism, vasodilation and transmission of nerve impulses. A wide number of vascular diseases as well as various immune and neurodegenerative disorders were found to be directly [...] Read more.
Nitric oxide (NO) is a key signaling molecule that acts in various physiological processes such as cellular metabolism, vasodilation and transmission of nerve impulses. A wide number of vascular diseases as well as various immune and neurodegenerative disorders were found to be directly associated with a disruption of NO production in living organisms. These issues justify a constant search of novel NO-donors with improved pharmacokinetic profiles and prolonged action. In a series of known structural classes capable of NO release, heterocyclic NO-donors are of special importance due to their increased hydrolytic stability and low toxicity. It is no wonder that synthetic and biochemical investigations of heterocyclic NO-donors have emerged significantly in recent years. In this review, we summarized recent advances in the synthesis, reactivity and biomedical applications of promising heterocyclic NO-donors (furoxans, sydnone imines, pyridazine dioxides, azasydnones). The synthetic potential of each heterocyclic system along with biochemical mechanisms of action are emphasized. Full article
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14 pages, 4725 KiB  
Article
Synthesis of 1-(2-Fluorophenyl)pyrazoles by 1,3-Dipolar Cycloaddition of the Corresponding Sydnones
by Denisa Dumitrescu, Sergiu Shova, Constantin Draghici, Marcel Mirel Popa and Florea Dumitrascu
Molecules 2021, 26(12), 3693; https://doi.org/10.3390/molecules26123693 - 17 Jun 2021
Cited by 3 | Viewed by 3071
Abstract
3-Arylsydnones bearing fluorine and bromine atoms on the benzene ring were synthesized from N-nitroso-2-fluorophenylglycines and characterized by NMR spectroscopy. These were employed further in synthesis of the corresponding 1-(2-fluorophenyl)pyrazoles by 1,3-dipolar cycloaddition reaction with dimethyl acetylenedicarboxylate (DMAD) as activated dipolarophile. The sydnones [...] Read more.
3-Arylsydnones bearing fluorine and bromine atoms on the benzene ring were synthesized from N-nitroso-2-fluorophenylglycines and characterized by NMR spectroscopy. These were employed further in synthesis of the corresponding 1-(2-fluorophenyl)pyrazoles by 1,3-dipolar cycloaddition reaction with dimethyl acetylenedicarboxylate (DMAD) as activated dipolarophile. The sydnones as reaction intermediates were characterized by single crystal X-ray diffraction analysis showing interesting features such as halogen bonding as an important interaction in modeling the crystal structure. Full article
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13 pages, 1069 KiB  
Article
A Facile Synthesis and Antimicrobial Activity Evaluation of Sydnonyl-Substituted Thiazolidine Derivatives
by Mei-Hsiu Shih, Yu-Yuan Xu, Yu-Sheng Yang and Guan-Ling Lin
Molecules 2015, 20(4), 6520-6532; https://doi.org/10.3390/molecules20046520 - 13 Apr 2015
Cited by 14 | Viewed by 6462
Abstract
Some new sydnonyl-substituted thiazolidine derivatives were synthesized in high yields by the modified Knoevenagel condensation of 3-aryl-4-formylsydnones with thiazolidine-2,4-dione and 2-thioxo-thiazolidine-4-one, respectively. All the synthesized thiazolidine derivatives were screened by paper-disc method to identify their antimicrobial activities against three bacteria viz. Staphylococcus aureus [...] Read more.
Some new sydnonyl-substituted thiazolidine derivatives were synthesized in high yields by the modified Knoevenagel condensation of 3-aryl-4-formylsydnones with thiazolidine-2,4-dione and 2-thioxo-thiazolidine-4-one, respectively. All the synthesized thiazolidine derivatives were screened by paper-disc method to identify their antimicrobial activities against three bacteria viz. Staphylococcus aureus, Proteus vulgaris and Escherichia coli, and two fungal cultures viz. Aspergillus niger and Penicillium citrinum. The reference drugs were Norfloxacin and Griseofulvin, respectively. The screening data indicated that the tested sydnonyl-substituted thiazolidine derivatives exhibited no obvious antibacterial activity compared with the standard drug Norfloxacin. However, thiazolidine derivatives displayed significant antifungal activities against Penicillium citrinum and Aspergillus niger. Notably, all of the tested compounds showed growth inhibitory activity 1.5-4.4 times higher than that of the standard drug Griseofulvin against the two fungi. Full article
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