8-Hydroxyquinoline Glycoconjugates Containing Sulfur at the Sugar Anomeric Position-Synthesis and Preliminary Evaluation of Their Cytotoxicity

Glycoconjugates: Advances in modern medicines and human health

Glycans and their glycoconjugates are complex biomolecules that are crucial for various biological processes. Glycoconjugates are found in all domains of life. They are covalently linked to key biomolecules such as proteins and lipids to play a pivotal role in cell signaling, adhesion, and recognition. The diversity of glycan structures and the associated complexity of glycoconjugates is the reason for their role in intricate biosynthetic pathways. Glycoconjugates play an important role in various diseases where they are actively involved in the immune response as well as in the pathogenicity of infectious diseases. In addition, various autoimmune diseases have been linked to glycosylation defects of different biomolecules, making them an important molecule in the field of medicine. The glycoconjugates have been explored for the development of therapeutics and vaccines, representing a breakthrough in medical science. They also hold significance in research studies to understand the mechanisms behind various biological processes. Finally, glycoconjugates have found an emerging role in various industrial and environmental applications which have been discussed here.

Recent progress in the synthesis of natural product inspired bioactive glycohybrids

Carbohydrates are a basic structural component that are indispensable to all cellular processes. In addition to being employed as chiral starting materials in the synthesis of a variety of natural products, carbohydrates are recognized as naturally occurring molecules having an enormous variety of functional, stereochemical, and structural properties. The understanding and biological roles of carbohydrate derived molecules can be greatly improved by selectively synthesizing functional carbohydrates through incorporating them with privileged scaffolds. For a deeper understanding of their roles and the development of functional materials based on sugar, it is crucial to develop new techniques for efficiently synthesizing, functionalizing, and modifying carbohydrates. Glycohybrids have a wide range of structural and functional characteristics along with protein-carbohydrate interactions that are crucial to mammalian biology and a number of disease states. This review, consisting the literature from January 2017 to July 2023 and provide an overview of recent developments in the chemical synthesis of glycohybrids based on natural product scaffolds of coumarin, quinolone, naphthalene diimide, indole, isatin, naphthoquinone, imidazole and pyrimidine. The biological activity of active glycohybrids are discussed in this review.

New syntheses of thiosaccharides utilizing substitution reactions

Novel synthetic methods published since 2005 affording carbohydrates containing sulfur atom(s) are reviewed. The review is divided to subchapters based on the position of sulfur atom(s) in the sugar molecule. Only those methods that take advantage of substitution are discussed.

Glycoconjugation of Quinoline Derivatives Using the C-6 Position in Sugars as a Strategy for Improving the Selectivity and Cytotoxicity of Functionalized Compounds

Based on the Warburg effect and the increased demand for glucose by tumor cells, a targeted drug delivery strategy was developed. A series of new glycoconjugates with increased ability to interact with GLUT transporters, responsible for the transport of sugars to cancer cells, were synthesized. Glycoconjugation was performed using the C-6 position in the sugar unit, as the least involved in the formation of hydrogen bonds with various aminoacids residues of the transporter. The carbohydrate moiety was connected with the 8-hydroxyquinoline scaffold via a 1,2,3-triazole linker. For the obtained compounds, several in vitro biological tests were performed using HCT-116 and MCF-7 cancer cells as well as NHDF-Neo healthy cells. The highest cytotoxicity of both cancer cell lines in the MTT test was noted for glycoconjugates in which the triazole-quinoline was attached through the triazole nitrogen atom to the d-glucose unit directly to the carbon at the C-6 position. These compounds were more selective than the analogous glycoconjugates formed by the C-1 anomeric position of d-glucose. Experiments with an EDG inhibitor have shown that GLUTs can be involved in the transport of glycoconjugates. The results of apoptosis and cell cycle analyses by flow cytometry confirmed that the new type of glycoconjugates shows pro-apoptotic properties, without significantly affecting changes in the distribution of the cell cycle. Moreover, glycoconjugates were able to decrease the clonogenic potential of cancer cells, inhibit the migration capacity of cells and intercalate with DNA.

Trastuzumab-conjugated oxine-based ligand for [89Zr]Zr4+ immunoPET

A new, bifunctional chelating ligand for immuno-Positron Emission Tomography (PET) was designed, synthesized, and conjugated to Trastuzumab for a proof-of-concept study with ⁸⁹Zr. H₄neunox was synthesized from the tris(2-aminoethyl)amine backbone, decorated with 8-hydroxyquinoline moieties, and utilizes a primary amine for functionalization. A maleimide moiety extends the chelator to create H₄neunox-mal for antibody conjugation via maleimide-thiol click chemistry. Preliminary ⁸⁹Zr radiolabeling of H₄neunox indicated quantitative radiolabeling at 1 × 10^-5 M, but improved inertness towards human serum (96% intact at 7 d) and Fe³⁺ (92% intact at 24 h) compared to the previously synthesized H₅decaox. The chelator was successfully conjugated to the monoclonal antibody, Trastuzumab, and used in preliminary radiolabeling reactions (37 °C, 2 h) with ⁸⁹Zr. Radiochemical assessments of the new H₄neunox-Trastuzumab conjugate include ⁸⁹Zr radiolabeling, spin filter purification, cell-binding immunoreactivity, and in vivo PET imaging and biodistribution in SKOV-3 tumour bearing nude mice, performed in comparison with the desferrioxamine B analog, DFO-Trastuzumab. The [⁸⁹Zr]Zr(neunox-Trastuzumab) showed lowered inertness towards serum (76% intact at 24 h) as well as demetallation in vivo through bone uptake (21% ID/g) in PET imaging and biodistribution studies when compared to [⁸⁹Zr]Zr(DFO-Trastuzumab). Although the combination of the chelator and antibody had detrimental effects on their intended purposes, nonetheless, the primary amine platform of H₄neunox developed here provides an oxine-based bifunctional ligand for further derivatizations with other targeting vectors.

Palladium Complexes Catalysed Telomerisation of Arylamines with Butadiene and Their Cyclisation into Quinoline Derivatives

Since alkynyl-arylamines are widely used in the chemical industry as pre products, a method of catalytic synthesis of problematic substituted quinolines from aromatic amines containing octadienal substituents has been developed. For this purpose, the processes of N-2,7-octa-dienyl anilines cyclisation under the action of transition metal complexes and telomerisation of arylamines with butadiene in the presence of palladium complexes were studied. Suppose N-2,7-octa-dienyl anilines are synthesised by telomerisation of arylamines with butadiene in the presence of palladium complexes. In that case, the cyclisation process is carried out in the presence of catalytic amounts of Pd(II) complex with dimethyl sulfoxide or nitrobenzene. The conducted research made it possible to study the opportunity of obtaining in one stage aromatic amines substituted in the nucleus by the reaction of butadiene with arylamines in the presence of palladium complexes. The research proved the principal possibility of obtaining ortho-substituted naphthylamines from butadiene and corresponding naphthylamines in one stage. A catalytic method for the synthesis of problematic substituted quinolines in the presence of palladium complexes has been developed. It has been established that the cyclisation of N-octadienyl-arylamines into quinolines proceeds through the stage of Kleisen amino rearrangement. N-2,7-octa-dienyl anilines and their derivatives can be widely used in the paint, pharmaceutical and chemical industries. Quinoline alkenylene derivatives can be used to produce unique polymer materials, hardeners, stabilisers, extractants, sorbing agents, catalysts for the synthesis of polyurethanes, biologically active substances and their analogues. They are pre-products in synthesising alkaloids, medicines and products used in agriculture. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Synthesis and Preliminary Evaluation of the Cytotoxicity of Potential Metabolites of Quinoline Glycoconjugates

The design of prodrugs is one of the important strategies for selective anti-cancer therapies. When designing prodrugs, attention is paid to the possibility of their targeting tumor-specific markers such as proteins responsible for glucose uptake. That is why glycoconjugation of biologically active compounds is a frequently used strategy. Glycoconjugates consisting of three basic building blocks: a sugar unit, a linker containing a 1,2,3-triazole ring, and an 8-hydroxyquinoline fragment was described earlier. It is not known whether their cytotoxicity is due to whole glycoconjugates action or their metabolites. To check the biological activity of products that can be released from glycoconjugates under the action of hydrolytic enzymes, the synthetically obtained potential metabolites were tested in vitro for the inhibition of proliferation of HCT-116, MCF-7, and NHDF-Neo cell lines using the MTT assay. Research shows that for the full activity of glycoconjugates, the presence of all three building blocks in the structure of a potential drug is necessary. For selected derivatives, additional tests of targeted drug delivery to tumor cells were carried out using polymer nanocarriers in which they are encapsulated. This approach significantly lowered the determined IC₅₀ values of the tested compounds and improved their selectivity and effectiveness.

Glycoconjugation of Betulin Derivatives Using Copper-Catalyzed 1,3-Dipolar Azido-Alkyne Cycloaddition Reaction and a Preliminary Assay of Cytotoxicity of the Obtained Compounds

Pentacyclic lupane-type triterpenoids, such as betulin and its synthetic derivatives, display a broad spectrum of biological activity. However, one of the major drawbacks of these compounds as potential therapeutic agents is their high hydrophobicity and low bioavailability. On the other hand, the presence of easily transformable functional groups in the parent structure makes betulin have a high synthetic potential and the ability to form different derivatives. In this context, research on the synthesis of new betulin derivatives as conjugates of naturally occurring triterpenoid with a monosaccharide via a linker containing a heteroaromatic 1,2,3-triazole ring was presented. It has been shown that copper-catalyzed 1,3-dipolar azide-alkyne cycloaddition reaction (CuAAC) provides an easy and effective way to synthesize new molecular hybrids based on natural products. The chemical structures of the obtained betulin glycoconjugates were confirmed by spectroscopic analysis. Cytotoxicity of the obtained compounds was evaluated on a human breast adenocarcinoma cell line (MCF-7) and colorectal carcinoma cell line (HCT 116). The obtained results show that despite the fact that the obtained betulin glycoconjugates do not show interesting antitumor activity, the idea of adding a sugar unit to the betulin backbone may, after some modifications, turn out to be correct and allow for the targeted transport of betulin glycoconjugates into the tumor cells.