Recent Advances in the Synthesis of Bioactive Glycohybrids via Click-Chemistry

Carbohydrates, traditionally known for their energy-provid-ing role, have gained significant attention in drug discovery due to their diverse bioactivities and stereodiversity. However, pure carbohydrate molecules often exhibit limited bioactivity and suboptimal chemical and physical characteristics. To address these challenges, functional groups with bioactive scaffolds have been incorporated into carbohydrate to enhance their bioactivity and improve their overall properties. Among the various synthetic methods available, click chemistry has emerged as a powerful tool for the synthesis of carbohydrate-contain-ing bioactive scaffolds, known as glycohybrids. Click chemistry offers several advantages, including high chemo-and regioselectivity, mild reaction conditions, easy purification, and compatibility with multiple functional groups. In the present review, we have emphasized the recent advances and most pertinent research on the development of 1,2,3-triazole-containing glycohybrids using the click reaction, their biological evaluations and the structure-activity relationship during 2017–2023. These newly synthesised glycohybrids could potentially be developed as new chemical entities (NCE) in pharmaceutical chemistry and may encourage the use of carbohydrates in drug discovery processes.


Introduction
The 1,3-dipolar cycloaddition reaction between terminal alkynes and azides was first discovered by Huisgen, and brought back into focus by Sharpless and others when they introduced the idea of 'click chemistry'. 1 Chemical transformations that are energetically favoured, precise, adaptable and result in a single reaction product with high yield are referred by the snappy name 'click'.In other words, simplicity and effectiveness are the fundamental components of 'click' chemistry. 2The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) to regioselectively form 1,2,3-triazoles reaction has emerged as the most successful click chemistry reaction for the development of new molecules with useful chemical properties, delivering an impressive volume of diverse molecules in a short amount of time (Figure 1). 3 The initial process, called the Huisgen cyclization, required heat treatment of both reagents and produced the respective triazoles (1,4-vs.1,5-substituted) as a 1:1 mixture with no regioselectivity at all. 4 The idea of 'click chemistry' has been put out as a potent instrument for joining two molecules together quickly and frequently without the production of side products. 5Because of their powerful dipole moments and exceptional stability to hydrolysis and oxidative/reductive conditions, these kinds of compounds can actively engage in hydrogen bonds and dipole-dipole interactions in biological systems. 6Linking small drug-like molecules to carbohydrates via click chemistry appears to be a powerful, highly accurate and selective reaction that may produce diverse molecules in rapid and consistent manner. 7Due to its high degree of dependability, full specificity, and the biocompatibility of the reactants, the 1,2,3triazole production from azides and terminal acetylenes has become an effective tool for the development of new

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medicinal scaffolds.When a triazole moiety is incorporated in a pharmacophore, it can either perform a passive or active function.A non-labile covalent spacer between discrete N-1 and C-4 or C-5 substituents is provided by the triazole when it functions passively.As an alternative, the triazole contributes when it acts in an active capacity by interacting with the biological target directly. 8arbohydrates belong to a class of molecules that are found both inside and on the surface of cells as glycoconjugates, have been found to be essential for a number of pathological and physiologically important biological processes, including cellular recognition, adhesion, migration, invasion, communication, bacterial/viral infection, tumour metastasis, and posttranslational modifications of proteins. 9,10gure 1 Typical chemical pathway resulting in 1,2,3-triazole linked molecules 11 Glycohybrids or carbohybrids are a family of hybrid molecules that contain carbohydrate molecules merged, fused or linked with several natural product scaffolds.The bioactive natural product scaffolds attached with carbohydrate motif have extra benefits for ADME (absorption, distribution, metabolism, and excretion).Furthermore, the bioactivity of medicinal molecules can be increased when carbohydrate molecules are coupled to bioactive scaffolds. 12arbohydrates are one of the best structural moieties for diversity-oriented synthesis since they have several stereocentres and may be used for carbohydrate-based drugs and materials. 13,14Carbohydrate diversity is frequently preceded by glycosylation utilising glycosyl donors.The synthesis of glycosyl donors can be tedious and the process might be challenging to perform.In order to overcome the difficulties in conventional glycosylation, a considerable number of azidosugars (or glycosyl azides) can be synthesized and attached to aglycone by 1,3-cycloaddition. 15Thus, click chemistry has been used extensively for the synthesis of glycohybrids, glycoconjugates and carbohydrate macrocycles in the area of carbohydrate chemistry, in which a sugar with an azido function is grafted onto a saccharide, peptide, or polymeric chain and the production of glycosidase inhibitors has also been achieved using this method. 16

CuAAC Click Chemistry Mediated Synthesis of Triazole-Based Glycohybrids and their Biological Activities
In this review, recent developments on synthesis of glycohybrids via click chemistry and their biological activity have been summarized.Marchiori and co-workers synthesized a series of triazole-linked galactosyl arylsulfonamides 16-22 by the click cycloaddition reaction of the azide-arylsulfonamides 1-7 with the alkyne-based sugar 3-O-propynyl-GalOMe 8, 17 followed by deacetylation of compounds 9-15 (Scheme 1). 18heme 1 Synthesis of triazole-linked galactosyl arylsulfonamides 16- 22   The Trypanosoma cruzi cell invasion inhibition experiments revealed that compounds 18 and 20, with the corresponding 5-methylisoxazole and 2,4-dimethoxypyrimidine groups, displayed lower values of infection index (ca.20) in T. cruzi cell invasion inhibition assays among the synthesized compounds 16-22; these compounds also displayed higher binding affinities to galectin-3 (EC 50  17-18 M) in Corning Epic label-free assays.So, the discovery of compounds 3 and 5 as possible galectin-3 binding-related T. cruzi cell invasion blockers reveal galectin-3 as a crucial host target for the development of new antitrypanosomal medicines.
Amdouni and co-workers synthesized nucleoside analogues 26a-f and 29a-q, with 1,4,5-trisubstituted 1,2,3-triazole aglycones, by utilising simple tandem click/electrophilic addition and tandem click/oxidative coupling methods, respectively.In this synthesis they used modified CuAAC approaches that enable the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles and thereby enhance structural modularity, as opposed to conventional CuAAC, which only generates 1,4-disubstituted 1,2,3-triazoles and narrows the accessible structural diversity.They used two methods to produce fully decorated 1,2,3-triazoles; the first was The HIV reverse transcriptase (RT) inhibiting properties of the pentacyclic iminosugars 37a-c, 38a,b, and their corresponding protected precursors 35a-c, and 36a,b, were investigated.It was showed that all substances may successfully block RT activity.The one with the highest RT inhibitory action, compound 35c, had an IC 50 value of 0.69 M.The structural activity relationship (SAR) study suggested that the multicyclic inhibitors' antiHIV-RT inhibitory efficacy could gain from an increase in hydrophilicity.

Scheme 7 Synthesis of compounds 49 and 50
Evaluation of the inhibitory activity of compounds 49, 50, 54 and 55 against -1,4-galactosyltransferase 1 (b4GalT), a commercially available enzyme, revealed that compound 54 inhibited the enzyme in the mM range.Addi-tionally, the MTT assay was used to assess the anticancer efficacy of glycohybrids 49, 50, 54 and 55 (Table 1).Ruiz and co-workers synthesized six carbohydrate naphthalene diimide conjugates 62-67 by click cycloaddition reaction of azido glycosides 45, 57-59 32,33 and 2-azidoethyl glycoside 60-61 34 with 2-N-propargyl naphthalene diimide 56 in the presence of sodium ascorbate, CuSO 4 and t-BuOH/H 2 O (1:1, v/v) at room temperature.In this synthesis, 2-N-propargyl naphthalene diimide, 56 was synthesized by the imidation of 2,6-dibromo-1,4,5,8-naphthalenetetracarboxylic dianhydride in the presence of N′,N′-dimethyl-1,3-propanediamine followed by nucleophilic aromatic substitution at 75 °C in the presence of an excess of propargylamine and acetonitrile (Scheme 9). 35o test their potential selectivity in G4 binding and cell penetration, six carbohydrate naphthalene diimide conjugates (carb-NDIs) were synthesized as G4 ligands.Carb-NDIs have demonstrated some selectivity for G4 structures over DNA duplexes, although various sugar moieties have no impact on determining whether one G4 topolog is preferred over another.Interestingly, the cellular absorption of monosaccharides that were connected to the NDI scaffold through a short ethylene linker was two to three times more effective than when the sugar was directly attached through its anomeric position.

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Compounds 74a-d and 75a-d possess coumarin derivatives linked to the trizole ring attached to a sugar moiety through oxymethylene (Scheme 11), whereas in the case of compounds 80a-d and 81a-d, coumarin derivatives are linked directly to the triazole ring containing sugar moiety (Scheme 12).All the synthesized compounds mentioned above were tested for their efficacy against the multidrug resistant clinical isolate 591 and the M. tuberculosis susceptible reference strain H 37 Rv.According to the findings, the antimycobacterial activity of the conjugates with the oxymethylene linker, namely 74a-d and 75a-d, were greater than that of the conjugates with direct linkage, namely 80a-d and 81a-d (Table 3); the most effective compounds were compounds 74c, 75b, and 75c, with MICs ≤5.2 M against the sensitive reference strain H 37 Rv and MICs ≤10.3 M against the multidrug-resistant clinical isolate 591.The most bactericidal compound 75b and its directly linked conjugate 81b shows inhibition against bacterial enzymes InhA and DNA gyrase B and interferes with the constitution of the cell wall to exhibit its antimycobacterial activity.
Furthermore, the synthesized compounds were not harmful, according to a cytotoxicity investigation employing the MTT test on compounds 74c, 75a, 75b, 75c, 81b, and 81c on THP-1 macrophage cell line.

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All synthesized compounds were tested for their inhibitory efficacy against -1,4-GalT, which is commercially available.The findings show that the kind of connected sugar and the presence of the protective groups in the sugar moiety are both important for action against -1,4-GalT.Compared to analogues containing a D-galactose unit, glycohybrid derivatives of D-glucose (89 and 91) are more active.Furthermore, derivatives with acetyl protection groups on the sugar unit do not exhibit enzyme inhibitory activity; only glycohybrids having an unprotected sugar portion do (Table 4).Seven cell lines HeLa, HCT 116, MCF-7, U-251 and Hs683, PANC-1 and AsPC-1 were used to test the cytotoxic activity of quinoline derivatives 83 and 84, as well as the resulting glycohybrids 85-92.The results of the cytotoxicity assay showed that glycohybrids 85 and 86 demonstrated promising outcomes among all the tested compounds (Table 5).Compound 86 appeared most active among glycohybrids that were tested against all additional cell lines, while 85 was active only against PANC-1.

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protection of corresponding monosaccharides with either trichloroethylidene (for ribose) or isopropylidene (for mannose and glucose), after that the addition of a leaving group and its exchange with sodium azide [58][59][60][61] and propargylated nucleobases 101-104 62 were synthesized by the propargylation of nucleobases (uracil, thymine, 5-fluorouracil, and adenine) with propargyl bromide in the presence of K 2 CO 3 in DMF solvents at 50 °C for 8-12 h.
After the successful synthesis of the triazolylmethyllinked nucleoside derivatives 105-116, the cytotoxic potential of each synthesized substance was tested against five distinct human cancer cell lines.Among the tested compounds, nucleoside derivative 111 was shown to be the most effective cytotoxic agent, with promising potential against colon cancer HCT-116 cells (IC 50 value of 35.6 M).The nucleoside derivative 108 displayed respectable efficacy against liver cancer Hep3B cells in comparison to most substances, and it was shown that all nucleoside derivatives were effective in inhibiting the Hep3B cell line and had good efficacy against the other evaluated cell lines.
Igual and co-workers synthesized glucopyranoside triazole derivatives 123a-l using 1,3-dipolar cycloaddition (CuAAC) reaction of the glucosyl azide 120 with terminal alkynes 121a-l in the presence of CuSO 4 •5H 2 O and sodium ascorbate (Scheme 16). 63In this synthesis, the first precursor, glucosyl azide, was synthesized by three processes.Firstly the very unstable glycosyl bromide was produced by treating glucosamine hydrochloride 117 with acetyl bromide, and it was then employed immediately in the subsequent glycosidation process to produced methyl 3,4,6-tri-Oacetyl-2-amine-2-deoxy-D-glucopyranoside (119) in the presence of MeOH and pyridine, which has the free amine group at the C-2 position.Glucosyl azide 120 was then synthesized by the reaction of 119 with triflyl azide solution in the presence of pyridine solvent. 64,65heme 16 Synthesis of glucopyranoside triazole derivatives 123a-l After the synthesis, compounds 123a-l were tested for their cytotoxicity and inhibitory activity.According to the MTT experiments, none of the compounds were cytotoxic.Western Blot analysis and subsequent inhibitory experiments showed that the most effective and selective compounds in the series were 123a (IC 50 = 0.50±0.02M, OGA), 123k (IC 50 = 0.52±0.01M, OGA), and 123l (IC 50 = 0.72±0.02M, OGA).

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Carmona and co-workers developed a series of dimeric iminosugars (126a-l, 127a-l, and 128a-l) by the click cycloaddition reaction of three distinct alkynyl pyrrolidines (126, 127 and 128) with a group of diazides (a-l) in the presence of CuSO 4 •5H 2 O, sodium ascorbate and t BuOH/H 2 O (Scheme 17 and Scheme 18). 66In this synthesis, precursors alkynyl pyrrolidine 127 and 128 was synthesized from D- lyxose, 67 and (pyrrolidin-2-yl)furan 126 was synthesized by the deprotection of 125b, which was obtained by the chromatographic separation of reaction mixture of 125a and 125b, produced via the conventional amide coupling of epimeric acids 124 68 with propargyl amine.

Scheme 18 Synthesis of compounds 126a-l, 127a-l and 128a-l
After the synthesis, the resultant crude dimers were evaluated in situ against one -galactosidase (126a-l) and two -fucosidases (127a-l and 128a-l).This technique is advanced as trying to identify divalent glycosidase inhibitors.Dimer 126e was found to be the best inhibitor of -galactosidase from bovine liver (K i = 5.8 M), while dimer 127i was found to be the best inhibitor of -fucosidases from bovine kidney (K i = 0.15 nM) and Homo sapiens (K i = 60 nM) (Table 6).with a propargyl group, which can be produced by substituting the side chain of the L-alanine, respectively.In this synthesis, compound 131 was synthesized from commercially available Fmoc-protected propargyl glycine by removing the fluorenylmethyloxycarbonyl (Fmoc) group and the solid-phase peptide synthesis (SPPS) procedure was used to synthesize the propargyl-modified peptides 132-133 utilising a Fmoc protection method (Scheme 19). 69fter the synthesis of compounds 135, 136 and 137, their inhibitory actions were evaluated and it was found that glycopeptide E-(TriazoleNeu5Ac2en)-AKE (137) and compound (TriazoleNeu5Ac2en)-A (135) were selective inhibitors of Vibrio cholerae sialidase, whereas glycopeptide analogue (TriazoleNeu5Ac2en)-AdE (136) inhibited both Vibrio cholerae and A. ureafaciens sialidases.

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Zuffo and co-workers developed sugar-NDI conjugates (180-203) by the click cycloaddition reaction of azide-NDI (166 and 167) with alkynyl glycosides (168-179) [73][74][75][76][77][78] in the presence of CuSO 4 •5H 2 O, sodium ascorbate and t BuOH/H 2 O (1:1) at room temperature (Scheme 21). 79In this synthesis the first precursor, azide-NDI (166 and 167) derivatives were synthesized in three steps i.e., after the initial imidation, which produced 165 80 from 164, the 3-azido-1-pro-panamine moiety was added through an S N Ar reaction and in the presence of excess diamine, the precursor and product undergo competitive dehalogenation, producing the desired dehalogenated product 166 as well as the brominated NDI and, after that, compound 167 was synthesized through a second MW-assisted SNAr process on brominated NDI in the presence of N,N-dimethylpropanediamine as the solvent.The authors evaluated the in vitro antiparasitic ac-   After the synthesis, all the compounds were tested for antimicrobial activity against Gram-positive (Micrococcus luteus CCM 331, Bacillus subtilis CCM 2216, Paenibacillus larvae CCM 4483 and P. larvae CCM 4486) and Gram-negative (Escherichia coli CCM 3954, Serratia marcescens CCM 8587) bacterial strains and it was found that four out of six 214a-f were active against G(+) strains and 214e was active against P. larvae CCM 4483 only, with moderate bactericidal activity (MIC 100 200 M) and all G(+) strains were sensitive to conjugates 214a, 214c and 214d.All four of the tested G(+) strains were equally active against the conjugates made from glucose 214a and galactose 214c (MIC 100 200 M).Xylose conjugate 214d was found to be strongest inhibitor of all G+ strains and when the protecting benzyl groups from the quinoline unit of compounds 214a-f were removed, the activity of conjugates 215a-f was completely lost.
Li and co-workers synthesized 23 hederacolchiside A1 derivatives 220a-v and 219a-w by click cycloaddition reaction of compound 217 with differently substituted aromatic azides 218a-w 82 in the presence of sodium ascrobate, Cu-SO 4 •5H 2 O and t-BuOH-H 2 O (2:1, v/v) at 50 °C (Scheme 24). 83In this synthesis, alkyne 217 was synthesized by stirring the reaction mixture of compound 216 with prop-2yn-1-amine and EDCI•HCl in the presence of pyridine at room temperature for 2 h.The synthetic compounds were tested for their in vitro inhibitory activities against two suspension leukaemia cell lines (HL60 cells and U937 cells) as well as four adherent human cancer cell lines (prostate cancer PC3 cells, colon carcinoma HT29 cells, hepatocellular carcinoma HepG2 cells, and lung cancer A549 cells) and, according to the preliminary SAR study, the majority of para-and meta-substituted compounds showed excellent broad-spectrum cytotoxic activity in vitro, particularly compound 220f (IC 50 = 0.54±0.10,0.93±0.08,0.54±0.06,2.66±0.09μM, respectively), which was more potent than the positive controls hederacolchiside A1 (0.85±0.08, 4.77±0.55,4.21±0.30,5.41±0.09μM, respectively) and 5-fluorouracil (8.45±0.56,22.23±1.83,59.12±5.02,69.07±3.57μM, respectively) against all tested human cancer cell lines.The findings of the cell cycle analysis and apoptosis assay also showed that 220f could clearly stop the growth of HepG2 cancer cells by causing apoptosis and inhibiting the cell cycle at the G1 and S phases.
Ottoni and co-workers synthesized a series of glycosidic derivatives of lawsone 222-229 by click cycloaddition reaction of 2-O-propargyllawsone (221) 84,85 with different peracetylated glycosyl azides 86,87      CuSO4, NaAsc, t-BuOH:H2O, rt HCl (1M): THF After the synthesis, a study of each triazole derivative's ability to inhibit two human glycosidases (GCase and galactosidase A) was conducted and it was found that -glucosidase from almonds and GCase were moderately to favourably inhibited by derivatives I, 231 and 240 and para-substitution at the phenyl group lowered the inhibitory efficacy of the derivatives against GCase in comparison to the original non-substituted drug I.The presence of halogens (diCl-, diBr-, diCF 3 -vs.diOMe-) in the 3,5-disubstitution pattern of the aromatic core also clearly enhanced the inhibition (238 vs. 240, diBr-vs.diOMe-).The corresponding C-2 epimers 242 and 249 were effective coffee bean galactosidase (IC 50 = 6.1-37 M) but mild inhibitors of human -galactosidase A. The effectiveness of the resultant lactams 251 and 252 (IC 50 = 1.8-2.0M) as inhibitors of almond -glucosidase was enhanced by pyrrolidine core oxi-dation at C-5 but this change reduced the inhibition of human -glucosidase.The inhibition of the human enzyme was similarly affected by the addition of a hydroxymethyl substituent at C-5 (compound 255), although in this case, the inhibition of the plant enzyme was not enhanced (IC 50 = 163 M for 255 vs. IC 50 = 8.0 M for I).
After the synthesis, triazoles 257a-t were tested in vitro for anti-microorganism activities and it was found that a number of triazoles were active against four strains of Gram-negative, three strains of Gram-positive bacteria (MICs = 1.56−6.25 M), with MICs ranging from 1.56 to 6.25 M; several triazoles were active against four strains of fungi.Triazoles 257c, 257d, 257f, 257h and 257r exerted anti-MRSA activities against all strains (MICs = 1.56−6.25 M) and their cytotoxicity against RAW 264.7 cells were quite low.

Table 7 Synthesis of Triazole Linked N-Glycopyranosides 270-289
After the synthesis, the anticancer activity of these newly synthesized triazole-linked N-glycosides of coumarins and quinolones was thoroughly evaluated against MCF-7 (breast cancer cell line), HepG2 (liver cancer cell line), HCT-116 (colon cancer cell line) and Huh-7.5 cell lines, and it was found that the chosen library member was selective-ly hazardous to the MCF-7 breast cancer cell line at low-micromolar concentrations (IC 50 10.97 mM).Compound 273 (Table 9) has anticancer action that is unique to cell lines, and mechanistic analyses revealed that the anticancer activity of the active compound was caused by the production of reactive oxygen species (ROS).

Review SynOpen Table 9 Anticancer Screening Results
Yan and co-workers synthesized a series of divalent oseltamivir 306-313 and guanidino oseltamivir 314-321 derivatives with esterification on the carboxyl acid group as powerful inhibitors of influenza virus neuraminidase.In this synthesis, oseltamivir 306-313 were synthesized by click cycloaddition reaction of the azide moiety 297-304 [102][103][104][105][106] with propargylated ethylene glycol 305 in the presence of CuSO 4 •5H 2 O, sodium ascorbate, THF/H 2 O, followed by the deprotection of the Boc group with trifluoroacetic acid (TFA); guanidino oseltamivir derivatives 314-321 were synthesized by the reaction of oseltamivir 306-313 with MeSC(=NBoc)NHBoc in the presence of HgCl 2 , Et 3 N, CH 2 Cl 2 at room temperature (Scheme 32). 107,108fter the synthesis, the authors evaluated Neuraminidase (NA) inhibition activity of the oseltamivir and guanidino oseltamivir derivatives, and it was found that the inhibitory activities of 314-321 were increased by the guanidino group, and submicromolar IC 50 values were found to be lower than those of the comparable animo divalent ana-logues 306-313.This results from significant electrostatic interactions between the more basic gaunidino group and the acidic peptide residues in the active site of NA.
Murray and co-workers synthesized saccharin-glycohybrids 325a-c by click cycloaddition of 6-azido saccharin derivative 322 with propargyl glucoside 323a-c in the presence of CuSO 4 •5H 2 O, sodium ascorbate and THF/H 2 O, followed by deprotection of acetyl groups of sugars in the presence of potassium methoxide, generated in situ from K 2 CO 3 and methanol.In this synthesis, 6-azido saccharin derivative 322 was synthesized in three steps starting from nitro-saccharin, and propargyl glucoside 323a-c were syn-

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thesized by the reaction of -D-galactose or -D-glucose pentaacetates with propargylic alcohol in the presence of BF 3 •Et 2 O (Scheme 33). 109fter the synthesis, the capability of compounds 325a-c to inhibit the soluble form of carbonic anhydrase (CA) IX (0.1 mg/mL) and CA II (0.1 mg/mL) was used to determine their inhibitory activity, and it was found that gluco and galacto molecules are comparable and that a longer linker enabled better interaction of the sugar with the selectivity pocket, resulting in outstanding CA IX selectivity.

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All newly synthesized compounds were tested in vitro for their inhibitory action against the three carbonic anhydrase (CA, EC 4.2.1.1)isozymes (hCA I, hCA II, and hCA IX), and effective inhibition against all three CA isoforms was seen; particularly, the tumour-related hCA IX for which it was found that compound 339g was the most powerful and selective inhibitor, with an inhibitory constant (IC 50 ) value of 7 nM, being four times more potent than the clinically utilised drug acetazolamide (AAZ) (IC 50 = 30 nM).Compound 339g was also found to have the most notable anticancer activity, and almost all compounds also shown modest antiproliferative effects against two cancer cell lines (HT29 and MDA-MB-231) in both hypoxia and normoxic settings.
Ruiz and co-workers synthesized symmetric 353-358 and dissymmetric 374-380 carbohydrate-phenyl ditriazole (carb-PDTZ).In this synthesis, symmetric carb-PDTZ 353-358 were synthesized by click cycloaddition reaction of protected 1-azidosugars of glucose 27h, 115 maltose 342, 116 fucose 343, 117 N-acetylglucosamine 344, 118,119 2-azidoethyl mannopyranoside 345, 120,121 and 2-azidoethylglucopyrano-side 346 122,123 with diethynylbenzene in the presence of Cu-SO 4 , Na-ascorbate, and H 2 O/THF (1:1) at 130 °C in a microwave for 30 min followed by deprotection of acetyl groups in the presence of NaOMe, MeOH (Scheme 35); the two successive click reactions-first, a mono-substitution with the appropriate azido sugar in the presence of CuSO 4 , Naascorbate, and H 2 O/THF (1:1) at 60 °C in microwave for 15-65 min, and then a second click reaction with the azidobenzene pyrrolidinyl moiety followed by deprotection of acetyl groups-were used to synthesize the dissymmetric carb-PDTZ 8-14 (Scheme 36). 124fter the synthesis, the potential antitumoral activity of all the synthesized compounds was also looked at by measuring their in vitro cytotoxicity on several cancer cell lines, and it was found that all carb-PDTZ derivatives had greater IC 50 values than the control PDTZ; likely because certain derivatives lacked compound stability and had reduced cellular absorption.
Malah and co-workers synthesized six novel carbohydrate-linked aryl-

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thoxyethoxy)ethoxy)-ethyl 3-azidobenzoate 381 and substituted aryl azide 386, with terminal alkyne groups of acetylated sugars 323a-b and 382, 125 in the presence of Cu-SO 4 , sodium ascorbate, TBTA and H 2 O/ t-BuOH/CH 2 Cl 2 at 25 °C (Scheme 37). 126fter the synthesis, the antibacterial activity of the synthesized molecules was analysed in comparison to Ampicillin against S. aureus and P. aeruginosa, while their antifungal activity was studied in comparison to Nystatin against Candida albicans and Aspergillus niger.Compound 384 was shown to have the strongest antibacterial activity among all the molecules, which clearly demonstrated the beneficial effects of the triethylene glycol sidearm and the acetylated sugar unit for the increased biological activity.

Scheme 38 Synthesis of precursors 394-396 and 397-399
After the synthesis, the novel quinoline glycohybrids were evaluated against the MCF-7, HCT-116 and NHDF-Neo cell lines for their in vitro cytotoxic activities, and it was found that only substances with acetyl protection of the hydroxyl groups in the sugar portion stopped the growth of tumour cells, and low activity was seen in derivatives with an unprotected sugar fragment.The glycohybrids 438-442, which have an extra heteroaromatic (5-amine-2-pyridyl) moiety in the linker structure, were found to be the most active among the tested compounds.When additional antiproliferative activity studies were conducted for compounds in the presence of Cu 2+ ions then it was found that when copper was present, the activity of glycohybrids was greatly enhanced compared to when cells were treated with Scheme 37 Synthesis of compounds 383-385 and 387-389

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just glycohybrids in the absence of Cu 2+ ; the strongest levels of cytotoxicity of the compounds was observed against the MCF-7 cell line.
After the synthesis, the inhibitory effect of each synthesized glycohybrid was evaluated against the MCF7 cell line and research on their anticancer showed that, with the exception of compounds 444 and 446d, all synthesized compounds reduced the development of MCF7 cells in a dosedependent way.However, these substances had a mild cytotoxic effect.
Chaidam and co-workers synthesized bis-triazole compounds 452a-ee from the reaction between various azide compounds and 1,6-di-propargyl benzyl glucoside 451 through the 1,3-dipolar cycloaddition reaction using Cu-SO 4 •5H 2 O and sodium ascorbate in THF at room temperature in good to excellent yields of 74-99% (Scheme 42). 145tarting compound 451, in turn, was prepared from the reaction of 1,6-dihydroxyl benzyl glucosides with propargyl bromide and sodium hydride in DMF.
The synthesized 1,6-bis-triazole-benzyl-glucoside derivatives 452a-ee were tested in vitro for their ability to inhibit -glucosidase from Saccharomyces cerevisiae using acarbose as a control.The synthesized glucoside derivatives displayed moderate to good activity with IC 50 values ranging from 3.73 to 53.34 M, which were far better than that of acarbose, with an IC 50 value of 146.25 M.Compound 452dd, with an IC 50 value of 3.73 M, was discovered to be the best inhibitor among the synthesized glucosides.Structure-activity relationship studies revealed that the activity increased to about three times (IC 50 of 3.86 M) after substituting a methoxy group at the ortho-and meta-position of benzyl ring 452f, as compared to the unsubstituted benzyl triazole compound 452a, with IC 50 of 12.07 M.In the

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same way, activity was found to decrease in the presence of electron-withdrawing groups like fluoro 452c and nitro 452d-e at the benzyl ring.
Ruysscher and co-workers synthesized LeuRS (clinically validated target for the development of antimicrobials) inhibitors containing different substituted triazoles.The first step in the synthetic process involved the commercially available allitol epoxide 453.The epoxide was made to open regio-and stereoselectively at the C2-position in a trans-diaxial manner by using the allylmagnesium chloride-based Gilman reagent.After the obtained alkene 454 underwent a hydroboration-oxidation reaction and selective tosylation of the ensuing primary alcohol, compound 457 was produced.This molecule next underwent in-situ azide substitution, enabling the coupling of a number of alkynes.Up to this point, the azide 458 was transformed into the isopropylidene protected alcohol 459.The acquired sulfamate functional group was then coupled to leucine to produce compound 461 through further sulfamoylation.By connecting 11 distinct alkynes using the standard azide alkyne click chemistry, the authors synthesized 10 protected molecules.Finally, the required compounds 463a-k were produced by acidic removal of all protecting groups (Scheme 43). 146 previously established in-vitro aminoacylation assay was used to confirm that all new leucine linked compounds 463a-k can inhibit LeuRS by observing the impact on the transfer of 14 C-radiolabeled leucine to tRNA Leu .Despite the presence of similar chemical structures, the inhibitory potential of compounds 463a-k was significantly affected by various triazole moiety replacements.With K i app values of 5.51 and 2.48 nM, the best compounds, 463a and 463k, carried a phenyl substituent at C13 on the triazole ring.Substituting the phenyl ring with electron-releasing or electron-

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withdrawing moieties resulted in a decrease of inhibitory activity, which suggested that the phenyl substituent was key to defining the stronger LeuRS inhibition.
Pingitore and co-workers synthesized two libraries of mono-and dimeric pyrrolidine iminosugars 465a-t and 466a-e by click cycloaddition reaction of azidohexylpyrrolidine 464 147 with the corresponding alkynes in the presence of CuSO 4 •5H 2 O, sodium ascorbate and t-BuOH/H 2 O (Scheme 44). 148After the synthesis, the crude reaction products were diluted in water and evaluated in situ against JbGlcNAcase at a concentration of 0.25 M, and it was found that the inhibitory efficacy of the starting material 464 was greatly enhanced by the majority of triazoles (465a-t), except for triazoles 465e and 465t, which clearly showed the lowest inhibitory potency (Table 11).No discernible changes in inhibition were seen based on the aromatic/aliphatic nature of the moiety connected to the triazole.

Scheme 44 Synthesis of mono-and dimeric pyrrolidine iminosugars 465a-t and 466a-e
Gulati and co-workers synthesized a series of triazolebased glycohybrids with both acetyl groups (468a-g) and free sugar hydroxyl groups (469a-g) by click cycloaddition reaction of anomeric azides of sugars with terminal acetylenes of tacrine (467) in the presence of CAN and CuI at room temperature (Scheme 45). 149In this synthesis, terminal acetylenes of tacrine was synthesized by the reaction of tacrine with propargyl bromide in the presence of sodium hydride.
After the synthesis, all the compounds were tested against AChE enzyme, and it was found that compounds 468a, 468c, 468d and 468g had good enzyme inhibition, with the most effective inhibitor being 468a, which was found to have an IC 50 value of 0.448 M.According to biological findings, various sugars (both acetylated and deacetylated) and their stereochemistry affect AChE inhibitory action in different ways and also deacetylated substances were less effective in inhibiting enzymes than acetylated substances.
Yang and co-workers synthesized a series of novel Calothrixin A (CAA) derivatives 473a-i by click cycloaddition reaction of compound 472 with different anomeric sugar azides in the presence of CuBr, N,N-diisopropylethylamine (DIPEA) and DMF at 50 °C (Scheme 46). 150In this synthesis, compound 472 was prepared by the reaction of Calothrixin B (470) 151 with propargyl bromide in the presence of KOH and DMF followed by oxidation with m-CPBA.
The synthesized CAA derivatives 473a-i were tested for their antiproliferative effects on cancer cell lines A549, MCF-7, A375, HCT116, and MDA-MB-231 with high levels of Topo I or II expression, the cancer cell line SH-SY5Y with low levels of Topo I and II expression, and human normal cell lines L02 and 293T, and it was found that 473g showed a significant antiproliferative activity against high Topo I and II expression cells A375 and HCT116, with IC 50 values of 20 and 50 nM, respectively, surpassing CAA, and showed no effect on human normal cells (IC 50 > 800 nM, against 293T).

Review SynOpen
naphthalentetracarboxylic dianhydride, in the presence of 3-(dimethylamino)-1-propylamine or 4-(2-aminoethyl)morpholine followed by nucleophilic aromatic substitution on the NDI in the presence of an excess of propargylamine in acetonitrile.
The synthesized compounds 482a-p were tested for their antiproliferative effects on colon cancer cells as well as their antiparasitic effects on the parasites T. brucei and L. major, and it was found that the sugar-NDI-NMe 2 derivatives were more toxic than the sugar-NDI-morph molecules in mammalian cells and parasites, and that O-carb-NDIs and S-carb-NDIs exhibit very minor differences in cytotoxicity, with the exception of non-cancerous human fibroblasts MRC-5, where thiosugar-NDIs frequently prove less hazardous.The best known chemical for carb-NDI derivatives is compound 282l (-malt-S-C2-NDI-NMe 2 ), which exhibits strong growth inhibition efficacy against colon cancer cells at sub-mM doses and exhibits remarkable selectivity over control human fibroblasts (9.8-fold).Dominska and co-workers synthesized a series of 8-hydroxyquinoline derivatives 487a-b, 488a-b, 495a-b and 492a-c by the click cycloaddition reaction of sugar derivatives 483, 484, 156,157 485, 486, 158,159 and 493, 494 160,161 with 8-(2-propyn-1-yloxy) quinoline 83, 52,129 and sugar derivatives 489, 490 162 with 8-(2-azidoethoxy)quinoline 491, 52,129 and 8-(3-azidopropoxy)quinoline 428 52,129 in the presence of CuSO 4 •5H 2 O, NaAsc, i-PrOH/THF/H 2 O (1:1:1, v:v:v) at room temperature (Scheme 48). 163fter the synthesis, a number of in vitro biological studies were carried out on the synthesized compounds utilising the cancer cells HCT-116 and MCF-7 as well as the healthy cells NHDF-Neo, and it was found that the glycohybrids with the triazole-quinoline connected through the triazole nitrogen atom to the D-glucose unit directly to the carbon at the C-6 position, showed the maximum cytotoxicity of both cancer cell lines in the MTT test.

Review SynOpen
Hodon and co-workers synthesized a series of glucose conjugates 500-503, 508-511 by click cycloaddition of the corresponding terpenic propargyl esters (497, 499, 505 and 507) with 2,3,4,6-tetra-O-acetyl--D-glucopyranosyl azide 27h or -D-glucopyranosyl azide 45 164 in the presence of CuI, and DMF at 40 °C (Scheme 49). 165fter the synthesis, the compounds were evaluated for cytotoxicity in eight cancer cell lines and two non-cancer cell lines, and it was found that they lost their selectivity against resistant cells, despite having enhanced cell penetration and substantial cytotoxicity in the CCRF-CEM cell line, and numerous studies revealed that most of them trigger apoptosis via the mitochondrial route.Compound 510 inhibits HCT116 and HeLa cell development and breaks down spheroid cultures, which is crucial for the treatment of solid tumours.
Wang and co-workers synthesized two types of glycosylated quercetins, Glu-Que 513a and 2Glu-Que 513b, by click cycloaddition reaction of 7-propargyl-quercetin 512a and 7,3′-dipropargyl-quercetin 512b with azido sugar 484 in the presence of CuSO 4 •5H 2 O, sodium ascorbate and t-BuOH/H 2 O at 50 °C, respectively (Scheme 50). 166In this synthesis, 7-propargyl-quercetin 512a and 7,3′-dipropargylquercetin 512b were synthesized by the reaction of quercetin with propargyl bromide in the presence of Na After the synthesis of compounds 513a (Glu-Que) and 513b (2Glu-Que), the neuroprotective properties of these compounds were evaluated, and it was found that 2Glu-Que 513b showed higher neuroprotective potential than Glu-Que 513a and this brought SOD, MDA, and GSH close to normal levels and reduced the ischemic area to 5.06%.

Scheme 52 Synthesis of compounds 517-518 3 Conclusions and Perspective
This paper has explored the recent advances in the synthesis of bioactive glycohybrids through the utilization of click chemistry.By investigating the potential of click chemistry in glycoscience, we have witnessed the emergence of a powerful tool for the development of diverse and complex glycohybrids as glycoconjugates with enhanced biological activities.Through click chemistry methodologies, researchers have successfully bridged the gap between synthetic chemistry and glycobiology, enabling the efficient construction of glycohybrids with precise control over their structures.The bioorthogonality and selectivity of click reactions have facilitated the conjugation of carbohydrates with various bioactive molecules, such as peptides, proteins, drugs and nanoparticles.

Review SynOpen
Herein, this review focuses on recent advancements and significant research in the development of glycohybrids containing 1,2,3-triazole moieties.These glycohybrids exhibit promising biological activities and have shown potential as new chemical entities in the pharmaceutical chemistry.The structure-activity relationships of these glycohybrids is explored, highlighting the influence of the 1,2,3triazole-containing bioactive scaffolds on their pharmacological properties.The integration of these glycohybrids in drug-discovery processes can open up new avenues for the utilization of carbohydrates in pharmaceutical chemistry.This review article has centred on the synthesis of triazolelinked glycohybrids through the well-established copper(I)catalyzed click chemistry method.These glycohybrids encompass a diverse range of molecules that exhibit significant biological activities, including anticancer, antiviral, antifungal, antimalarial, antitubercular, antibacterial, and carbonic anhydrase inhibition.These bioactive glycohybrids consist primarily of biologically relevant molecules, such as heterocyclic rings and hydrocarbon chains, connected to sugar moieties via triazole linkers using Cu(I)-catalyzed reactions.
The integration of click chemistry into glycoscience has revolutionized the synthesis of bioactive glycohybrids, enabling researchers to explore new frontiers in the development of biologically relevant molecules.The continued advancements in this field will undoubtedly contribute to the understanding of glycan functions and pave the way for innovative solutions in healthcare and biotechnology.The advancement of these glycohybrids as novel chemical entities holds great potential for the development of improved drugs and may pave the way for a renewed exploration of carbohydrates in the field of drug discovery.
Sagar received his Ph.D. in Organic Chemistry from Central Drug Research Institute (CDRI) Lucknow and University of Agra in 2006.After his Ph.D., he pursued his Research Associate with Prof. Y.D. Vankar at IIT Kanpur during 2006-2007.He pursued his first postdoctoral research at Seoul National University South Korea with Prof. Seung Bum Park during 2007-2008.He moved to University of Oxford and worked with Prof. Benjamin G. Davis as BBSRC postdoctoral fellow until August 2012.He returned to India in August 2012 and held a faculty position at Shiv Nadar University (SNU).He moved to Department of Chemistry, Banaras Hindu University (BHU) as Associate Professor in February 2018 and worked there until Jan 2020.He subsequently became a Full Professor at Jawaharlal Nehru University (JNU), New Delhi in January 2020 and is presently working there as Professor of Chemistry in School of Physical Sciences.His current research interests include devising newer ways for efficient chemical synthesis of natural product inspired small molecules, glycohybrids and glycopeptides implicated in various diseases including tuberculosis and cancer.Kavita Singh completed her M.Sc.from Deen Dayal Upadhyaya University, Gorakhpur, UP, India in 2019.She qualified as CSIR-JRF then joined the Glycochemistry laboratory of the School of Physical Sciences, Jawaharlal Nehru University, New Delhi, as a junior research fellow in 2021.She is currently pursuing her PhD degree under the supervision of Prof. Ram Sagar.Her work is focused on the development of new meth-ods for the synthesis of carbohydrate fused heterocyclic molecules as bioactive glycohybrids.She is also interested in medicinal chemistry and the synthesis of natural product inspired bioactive scaffolds.Rajdeep Tyagi completed his M.Sc. in 2018 from Kirorimal College, University of Delhi, New Delhi, India.He joined the Glycochemistry laboratory of School of Physical Sciences, Jawaharlal Nehru University, New Delhi, as a UGC junior research fellow in 2021.He is currently pursuing his Ph.D. degree under the supervision of Prof. Ram Sagar.His expertise lies in heterocyclic molecules, medicinal chemistry, organic synthe-sis, and the synthesis of indolebased bioactive glycohybrids.He is also interested in developing new methods for glycoconjugate synthesis and their bioapplications.Vinay Kumar Mishra completed his M.Sc.from Dr. Ram Manohar Lohia Avadh University UP, India.He joined the Glycochemistry lab of the Department of Chemistry, Institute of Science, Banaras Hindu University in 2019 to pursue his PhD degree under the supervision of Prof. Ram Sagar.His work is focused on development of new methods for the synthesis of carbohydrate fused heterocyclic molecules as glycohybrids.He is also interested in the synthesis of natural product inspired bioactive scaffolds.K. Singh et al.

22
Scheme 22 Synthesis of compounds 209a-f and 210a-f

Scheme 45 Scheme 47
Scheme 45 Synthesis of compounds 468a to 469g

Table 1
Results of the Test for Bovine Milk -1,4-Galactosyltransferase 1

Table 2
IC 50Values of against M. tuberculosis PtpB

Table 3
MIC, MBC and MBC/MIC Ratio of Some Tested Compounds and First-Line Drugs against M. tuberculosis Sensitive Reference Strain H 37 Rv and

Table 5
Screening of Cytotoxicity of Glycoconjugate Derivatives of 8- a Cytotoxicity was evaluated using MTT assay.b Incubation time 24 h.

Table 6
IC 50 and K i for Selected Dimers a
in the presence of Cu-SO 4 •5H 2 O, sodium ascorbate and THF/H 2 O at room temperature (Scheme 25).

Table 11
Inhibitory Potency of Monovalent Triazole Derivatives