Design, synthesis, and biological evaluation of novel 2,3-Di-O-Aryl/Alkyl sulfonate derivatives of l-ascorbic acid: Efficient access to novel anticancer agents via in vitro screening, tubulin polymerization inhibition, molecular docking study and ADME predictions

A series of novel l-ascorbic acid derivatives bearing aryl and alkyl sulfonate substituents were synthesized and characterized. In vitro anticancer evaluation against MCF-7 (breast) and A-549 (lung) cancer cell lines revealed potent activity for most of the compounds, with 2b being equipotent to the standard drug colchicine against MCF-7 (IC50 = 0.04 μM). Notably, compound 2b displayed 89-fold selectivity for MCF-7 breast cancer over MCF-10A normal breast cells. Derivatives with two sulfonate groups (2a-g, 3a-g) exhibited superior potency over those with one sulfonate (4a-c,5g, 6b). Compounds 2b and 2c potently inhibited tubulin polymerization in A-549 cancer cells (73.12 % and 62.09 % inhibition, respectively), substantiating their anticancer potential through microtubule disruption. Molecular docking studies showed higher binding scores and affinities for these compounds at the colchicine-binding site of α, β-tubulin compared to colchicine itself. In-silico ADMET predictions indicated favourable drug-like properties, with 2b exhibiting the highest binding affinity. These sulfonate derivatives of l-ascorbic acid represents promising lead scaffolds for anticancer drug development.

Green solvent-free synthesis of new N-heterocycle-L-ascorbic acid hybrids and their antiproliferative evaluation

Aim: The authors' aim was to improve the application of copper-catalyzed azide-alkyne cycloaddition in the synthesis of hybrids containing biologically significant nucleobases and L-ascorbic acid scaffolds by introducing an environmentally friendly and waste-free ball mill. Results: Two series of hybrids with a purine, pyrrolo[2,3- d]pyrimidine or 5-substituted pyrimidine attached to 2,3-dibenzyl-L-ascorbic acid via a hydroxyethyl- (15a–23a) or ethylidene-1,2,3-triazolyl (15b–23b) bridge were prepared by ball milling and conventional synthesis. The unsaturated 6-chloroadenine L-ascorbic acid derivative 16b can be highlighted as a lead compound and showed strong antiproliferative activity against HepG2 (hepatocellular carcinoma) and SW620 (colorectal adenocarcinoma) cells. Conclusion: Mechanochemical synthesis was superior in terms of sustainability, reaction rate and yield, highlighting the advantageous applications of ball milling over classical reactions.

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

Due to their intrinsic physical properties, which includes being able to perform as volatile liquids at room and biological temperatures, fragrance ingredients/intermediates make ideal candidates for continuous-flow manufacturing. This review highlights the potential crossover between a multibillion dollar industry and the flourishing sub-field of flow chemistry evolving within the discipline of organic synthesis. This is illustrated through selected examples of industrially important transformations specific to the fragrances and flavours industry and by highlighting the advantages of conducting these transformations by using a flow approach. This review is designed to be a compendium of techniques and apparatus already published in the chemical and engineering literature which would constitute a known solution or inspiration for commonly encountered procedures in the manufacture of fragrance and flavour chemicals.

Photocatalytic Oxygenation of Heterostilbenes—Batch versus Microflow Reactor

On the basis of earlier results with furan and thiophene derivatives of benzobicyclo[3.2.1]octadiene, photocatalytic oxygenation of novel furo- and thieno heterostilbenes with water-soluble manganese(III) porphyrins offered suitable possibilities to study their reactivities and reaction pathways depending on the heteroatom and the catalyst charge. The experiments were carried out in two reactors types (batch and microflow) to investigate the geometric effects. NMR spectroscopy, GC, and UPLC/MS analyses were applied for identification and quantification of the products. As our results indicated, the 2-thienyl and the common p-tolyl groups in the starting compounds remained intact due to their stronger aromaticity. Hence, the thieno derivative underwent oxygenation only at the open-chain part of the molecule, and the rates of its reactions were much lower than those of the furyl analogue. The less stable furan ring was easily oxygenated, its products with highest ratios were 2-furanon derivatives. Epoxide formation occurred at the open-chain parts of both substrates preferably by the anionic catalyst. Nevertheless, the conversion rates of the substrates were higher with the cationic porphyrin, according to electrophilic attacks by photogenerated Mn(V)=O species. Additionally, the reactions were significantly faster in microflow reactors due to the more favorable circumstances of mass transfer, diffusion, and light penetration.

1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides under "Non-Conventional" Conditions: Green Solvents, Irradiation, and Continuous Flow

The 1,3-dipolar cycloaddition reactions (DCs) of nitrile oxides (NOs) to alkenes and alkynes are useful methods for the synthesis of 2-isoxazolines and isoxazoles respectively, which are important classes of heterocyclic compounds in organic and medicinal chemistry. Most of these reactions are carried out in organic solvents and under thermal activation. Nevertheless the use of supercritical carbon dioxide (scCO₂ ) and ionic liquids (Ils) as alternative solvents and the application of microwave (MW) and ultrasound (US) as alternative activation procedures have evident advantages from the "Green Chemistry" point of view. The critical discussion on the applications of these "unconventional" activation methods and reaction conditions in the 1,3-DCs of NOs is the objective of the present Review.

Flow Chemistry for Cycloaddition Reactions

Continuous flow reactors form part of a rapidly growing research area that has changed the way synthetic chemistry is performed not only in academia but also at the industrial level. This Review highlights the most recent advances in cycloaddition reactions performed in flow systems. Cycloadditions are atom-efficient transformations for the synthesis of carbo- and heterocycles, involved in the construction of challenging skeletons of complex molecules. The main advantages of translating these processes into flow include using intensified conditions, safer handling of hazardous reagents and gases, easy tuning of reaction conditions, and straightforward scaling up. These benefits are especially important in cycloadditions such as the copper(I)-catalyzed azide alkyne cycloaddition (CuAAC), Diels-Alder reaction, ozonolysis and [2+2] photocycloadditions. Some of these transformations are key reactions in the industrial synthesis of pharmaceuticals.

Flow chemistry as a tool to access novel chemical space for drug discovery

This perspective scrutinizes flow chemistry as a useful tool for medicinal chemists to expand the current chemical capabilities in drug discovery. This technology has demonstrated his value not only for the traditional reactions used in Pharma for the last 20 years, but also for bringing back to the lab underused chemistries to access novel chemical space. The combination with other technologies, such as photochemistry and electrochemistry, is opening new avenues for reactivity that will smoothen the access to complex molecules. The introduction of all these technologies in automated platforms will improve the productivity of medicinal chemistry labs reducing the cycle times to get novel and differentiated bioactive molecules, accelerating discovery cycle times.

Flow Synthesis of Biologically-Relevant Compound Libraries

Flow chemistry is one of the most prominent enabling technologies that has greatly shaped the way chemists' approach organic synthesis. Specifically, in drug discovery, the advantages of flow techniques over batch procedures allow the rapid and efficient assembly of compound libraries to be tested for biological properties. The aim of the present review is to comment on some representative examples from the last five years of literature that highlight how flow procedures are becoming of increasing importance for the synthesis of biologically-relevant molecules.

Antitumor and antiviral activities of 4-substituted 1,2,3-triazolyl-2,3-dibenzyl-L-ascorbic acid derivatives

Two series of 6-(1,2,3-triazolyl)-2,3-dibenzyl-l-ascorbic acid derivatives with the hydroxyethylene (8a−8u) and ethylidene linkers (10c−10p) were synthesized and evaluated for their antiproliferative activity against seven malignant tumor cell lines and antiviral activity against a broad range of viruses. Conformationally unrestricted spacer between the lactone and 1,2,3-triazole units in 8a−8u series had a profound effect on antitumor activity. Besides, the introduction of a long side chain at C-4 of 1,2,3-triazole that led to the synthesis of decyl-substituted 2,3-dibenzyl-l-ascorbic acid 8m accounted for a selective and potent antiproliferative activity on breast cancer MCF-7 cells cells in the nM range. Further analysis showed that compound 8m strongly enhanced expression of hypoxia inducible transcription factor 1 α (HIF-1α) and to some extent decreased expression of nitric oxide synthase 2 (NOS2) suggesting its role in regulating HIF-1α signalling pathway. The p-methoxyphenyl-substituted derivative 10g displayed specific anti-cytomegalovirus (CMV) potential, whereas aliphatic-substituted derivatives 8l and 8m had the most potent, yet relatively non-specific, anti-varicella-zoster (VZV) activity.

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Two series of 1,2,3-triazolyl 2,3-dibenzyl-l-ascorbic acid conjugates were synthesized.

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Conformationally unrestricted spacer had a major effect on antitumor activities.

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Decyl-substituted l-ascorbic acid 8m caused inhibition of breast cancer MCF-7 cells in the nM range.

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8m increased the expression of hypoxia inducible transcription factor HIF-1α.

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p-Methoxyphenyl-substituted derivative 10g had specific anti-CMV activity.

The Antioxidant and Antiproliferative Activities of 1,2,3-Triazolyl-L-Ascorbic Acid Derivatives

The novel 4-substituted 1,2,3-triazole L-ascorbic acid (L-ASA) conjugates with hydroxyethylene spacer as well as their conformationally restricted 4,5-unsaturated analogues were synthesized as potential antioxidant and antiproliferative agents. An evaluation of the antioxidant activity of novel compounds showed that the majority of the 4,5-unsaturated L-ASA derivatives showed a better antioxidant activity compared to their saturated counterparts. m-Hydroxyphenyl (7j), p-pentylphenyl (7k) and 2-hydroxyethyl (7q) substituted 4,5-unsaturated 1,2,3-triazole L-ASA derivatives exhibited very efficient and rapid (within 5 min) 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) radical scavenging activity (7j, 7k: IC₅₀ = 0.06 mM; 7q: IC₅₀ = 0.07 mM). In vitro scavenging activity data were supported by in silico quantum-chemical modelling. Thermodynamic parameters for hydrogen-atom transfer and electron-transfer radical scavenging pathways of anions deprotonated at C2-OH or C3-OH groups of L-ASA fragments were calculated. The structure activity analysis (SAR) through principal component analysis indicated radical scavenging activity by the participation of OH group with favorable reaction parameters: the C3-OH group of saturated C4-C5(OH) derivatives and the C2-OH group of their unsaturated C4=C5 analogues. The antiproliferative evaluation showed that p-bromophenyl (4e: IC₅₀ = 6.72 μM) and p-pentylphenyl-substituted 1,2,3-triazole L-ASA conjugate (4k: IC₅₀ = 26.91 μM) had a selective cytotoxic effect on breast adenocarcinoma MCF-7 cells. Moreover, compound 4e did not inhibit the growth of foreskin fibroblasts (IC₅₀ > 100 μM). In MCF-7 cells treated with 4e, a significant increase of hydroxylated hypoxia-inducible transcription factor 1 alpha (HIF-1α) expression and decreased expression of nitric oxide synthase 2 (NOS2) were observed, suggesting the involvement of 4e in the HIF-1α signaling pathway for its strong growth-inhibition effect on MCF-7 cells.

Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

Copper-catalyzed mechanochemical click reactions using Cu(II), Cu(I) and Cu(0) catalysts have been successfully implemented to provide novel 6-phenyl-2-(trifluoromethyl)quinolines with a phenyl-1,2,3-triazole moiety at O-4 of the quinoline core. Milling procedures proved to be significantly more efficient than the corresponding solution reactions, with up to a 15-fold gain in yield. Efficiency of both solution and milling procedures depended on the p-substituent in the azide reactant, resulting in H < Cl < Br < I reactivity bias. Solid-state catalysis using Cu(II) and Cu(I) catalysts entailed the direct involvement of the copper species in the reaction and generation of highly luminescent compounds which hindered in situ monitoring by Raman spectroscopy. However, in situ monitoring of the milling processes was enabled by using Cu(0) catalysts in the form of brass milling media which offered a direct insight into the reaction pathway of mechanochemical CuAAC reactions, indicating that the catalysis is most likely conducted on the surface of milling balls. Electron spin resonance spectroscopy was used to determine the oxidation and spin states of the respective copper catalysts in bulk products obtained by milling procedures.