Lactoside Derivatives Research Articles

Synthesis of Galectin Inhibitors by Regioselective 3'-O-Sulfation of Vanillin Lactosides Obtained under Phase Transfer Catalysis.

Vanillin-based lactoside derivatives were synthetized using phase-transfer catalyzed reactions from per-O-acetylated lactosyl bromide. The aldehyde group of the vanillin moiety was then modified to generate a series of related analogs having variable functionalities in the para- position of the aromatic residue. The corresponding unprotected lactosides, obtained by Zemplén transesterification, were regioselectively 3′-O-sulfated using tin chemistry activation followed by treatment with sulfur trioxide-trimethylamine complex (Men3N-SO3). Additional derivatives were also prepared from the vanillin’s aldehyde using a Knoevenagel reaction to provide extended α, β-unsaturated carboxylic acid which was next reduced to the saturated counterpart.

Lactose derivatives as potential inhibitors of pectin methylesterases.

The discovery of molecules that can inhibit the action of phytopathogens is essential to find alternative to current pesticides. Pectin methylesterases (PME), enzymes that fine-tune the degree of methylesterification of plant cell wall pectins, play a key role in the pathogenicity of fungi or bacteria. Here we report the synthesis of new lactoside derivatives and their analysis as potential PME inhibitors using three plants and one fungal PME. Because of its structure, abundance and reduced cost, lactose was chosen as a case study. Lactoside derivatives were obtained by TEMPO-mediated oxidation of methyl lactoside, followed by an esterification procedure. Three derivatives were synthesized: sodium (methyl-lactosid)uronate, methyl (methyl-lactosid)uronate and butyl (methyl-lactosid)uronate. The inhibition of the plant and pathogen enzyme activities by lactoside derivatives was measured in vitro, showing the importance of the substitution on lactose: methyl (methyl-lactosid)uronate was more efficient than butyl (methyl-lactosid)uronate. These results were confirmed by docking analysis showing the difference in the interaction between lactoside derivatives and PME proteins. In conclusion, this study identified novel inhibitors of pectin remodeling enzymes.

Design, synthesis and evaluation of lactoside-derived galectin-3 inhibitors

Based on docking computation, a panel of lactoside derivatives have been designed as galectin-3 inhibitors. Suitable functional group modifications at C′-3 of methyl lactoside were predicted to supply some additional π–cation, π…H–O, and hydrogen bond interactions between the designed substrates and galectin-3 residues. The selected compounds, giving higher TotalScore in docking calculations, were thus synthesized, and their binding affinities toward galectin-3 were evaluated with SPR assay.

Regioselective Synthesis of Novel Galactose, Fucose and Lactose Fatty Acid Esters as Glycomimetics of Bile Acid 1-O-acyl Galactoside and Bacterial Glycolipids

Background: Carbohydrate fatty acid esters are found in important biological molecules such as bile acid 1-O-acyl galacto and bacterial glycolipids. The synthesis of glycomimetics of those biomolecules is required to study their structure-activity relationship. Method: In this work a series of carbohydrate fatty acid esters were regioselectively prepared mainly via protection and deprotection and tin-mediated strategies of partially benzyl-protected sugars, followed by hydrogenolysis of the benzyl groups. Results: We report here the regioselective synthesis of galactose palmitoyl esters along with other fatty acyl galactose glycomimetics namely fucose and lactose fatty esters. 1-O-palmitoyl-, 1,6-di-Opalmitoyl- D-galactose and 1-O-palmitoyl-L-fucose derivatives were prepared via a low-temperature esterification of the partially benzyl-protected galactose and fucose derivatives, respectively, followed by hydrogenolysis of the benzyl groups. The regioselective synthesis of 3'-O-acyl-D-lactosides of palmitic and nitrobenzoic acids was accomplished using a dibutyltin oxide activation strategy of partially protected lactoside derivatives. Conclusion: The regioselective synthesis of galactose, fucose and lactose fatty acid esters as glycomimetics of biological molecules containing the 1-O-fatty acyl-D-galactose moiety is reported in this work. Keywords: Glycolipid, glycomimetics, sugar fatty acid esters, regioselective esterification, dibutyltin oxide, bile acid.

Galectin-1-Specific Inhibitors as a New Class of Compounds To Treat HIV-1 Infection

Despite significant improvements, antiretroviral therapies against HIV-1 are plagued by a high frequency of therapeutic failures that have been associated with acquisition of drug resistance. We recently reported that HIV-1 exploits a host glycan binding protein, galectin-1, to increase its attachment to host cells, thereby increasing its overall infectivity in susceptible cells. This finding suggests that host molecules such as galectin-1 could reduce the expected efficiency of HIV-1 drugs targeting early steps of the replicative cycle, such as attachment and entry processes. Thus, new classes of drugs that would interfere with galectin-1/HIV-1 interactions could benefit the current antiretroviral therapy. To further explore this possibility, experiments were conducted to discover leading compounds showing specific inhibition of galectin-1 activity in a cellular model of HIV-1 infection. Three lactoside compounds were found to modestly inhibit the interaction of galectin-1 with primary human CD4(+) T cells. Interestingly, these same inhibitors reduced the galectin-1-mediated increase in HIV-1 attachment to target cells in a much more efficient manner. More important, the tested lactoside derivatives also significantly decreased the galectin-1-dependent enhancement of HIV-1 infection. These observations deserve further attention when considering that the development of new drugs to prevent and treat HIV-1 infection remains a priority.

Chemical synthesis using enzymatically generated building units for construction of the human milk pentasaccharides sialyllacto-N-tetraose and sialyllacto-N-neotetraose epimer

α,2-3- and α,2-6-sialylated lactosaminide precursor structures obtained by various enzymatic procedures could be used for glycosylations employing triflic acid/N-iodosuccinimide. Easily accessible selectively protected lactoside derivatives served as acceptor disaccharides to give the corresponding human milk pentasaccharides in good yields. These were characterized by spectroscopic means in the form of their peracetylated derivatives.

Synthesis of fluorescent alkyl lactoside derivatives

Fluorescent-labeled alkyl lactoside (NBD-alkyl lactoside) derivatives were synthesized by the reaction of NBD alkyl alcohol with heptaacetyllactosyl trichloroacetimidate in the presence of BF 3·Et 2O.

Synthesis of Lewis X and three Lewis X trisaccharide analogues in which glucose and rhamnose replace N-acetylglucosamine and fucose, respectively

Three analogues of the Le x trisaccharide: α- l-Fuc p-(1→3)-[β- d-Gal p-(1→4)]- d-GlcNAc p as well as the Le x trisaccharide itself were synthesized as methyl glycosides. In the analogues, either only the fucose residue is replaced by rhamnose or both the N-acetylglucosamine and the fucosyl residues are replaced by glucose and rhamnose, respectively. Our synthetic strategy relied on the use of lactoside and 2-azido lactoside derivatives as disaccharide acceptors, which were submitted to either fucosylation or rhamnosylation. Our results confirm that the reactivity of lactose in protection and glycosylation reactions is greatly affected by (1) the structure of the aglycone and (2) the presence of an azido substituent at C-2 of the glucose moiety. Thus, a methyl lactoside acceptor was easily glycosylated at O-3 with perbenzylated β-thiophenyl fucoside and rhamnoside to give anomerically pure α-fucosylated and α-rhamnosylated trisaccharides, respectively. In contrast, the same reactions on a 2-azido methyl lactoside acceptor led to the formation of anomeric mixtures. While the α- and β-fucosylated 2-azido trisaccharides could be separated by RP-HPLC, such separation was not possible for the rhamnosylated anomers. The desired rhamnosylated trisaccharide was finally obtained anomerically pure using an isopropylidene-protected rhamnosyl donor. The deprotection sequences also showed that the presence of a 2-azido substituent at C-2 of the glucose residue conferred stability to the vicinal fucosidic linkage at C-3. To test their relative affinity for anti-Le x Abs the Le x analogues will be used as competitive inhibitors against methyl Le x. In addition, their conformational behavior will be studied by NMR spectroscopy and molecular modeling experiments.

Efficient chemoenzymatic synthesis of biotinylated human serum albumin–sialoglycoside conjugates containing O-acetylated sialic acids

Sialyl Tn (STn) and sialyl lactoside derivatives containing O-acetylated sialic acid residues have been chemoenzymatically synthesized using a one-pot three-enzyme system and conjugated to biotinylated human serum albumin (HSA) using an adipic acid para-nitrophenyl ester coupling reagent. This approach provides an efficient and general protocol for preparing carbohydrate-protein conjugates containing base-sensitive groups.

Synthesis of multivalent lactose derivatives by 1,3-dipolar cycloadditions: selective galectin-1 inhibition

Acetylene derivatives of phenylalanine, phenethylamine and the multifunctional unnatural amino acids, phenyl-bis-alanine and phenyl-tris-alanine, were synthesized and functionalized with 2-azidoethyl β- d-galactopyranosyl-(1→4)-β- d-glucopyranoside via regioselective copper(I)-mediated 1,3-dipolar cycloaddition to give a panel of mono-, di- and trivalent lactoside derivatives. Evaluation of the compounds as inhibitors against the tumour- and inflammation-related galectin-1, -3, -4N, -4C, -4, -7, -8N and -9N revealed a divalent compound with a K d value as low as 3.2 μM for galectin-1, which corresponded to a relative potency of 30 per lactose unit as compared to the natural disaccharide ligand lactose. This divalent compound had at least one order of magnitude higher affinity for galectin-1 than for any of the other galectins investigated.

Efficient Sialylation on Azidododecyl Lactosides by Using B16 Melanoma Cells

Lactoside primers (dodecyl lactoside derivatives) resemble intermediates in the biosynthetic pathway of glycolipids and, therefore, act as substrates for cellular enzyme-catalyzed glycosylation. To establish the optimal condition for the bioproduction of a large amount of valuable materials containing GM3-type oligosaccharides, two kinds of lactoside primers having the azido group in different positions were synthesized and introduced into B16 melanoma cells. The saccharide chains of both primers were elongated by cells to give GM3-type oligosaccharide derivatives, which were released to the culture medium. The amount of glycosylated product from newly synthesized 2-azidododecyl beta-lactoside (primer II) was almost twice that from 12-azidododecyl beta-lactoside (primer I). The effects of seeded cell number, primer concentration, and length of incubation time on the glycosylation efficiency were also investigated. The results showed that the higher the seeded cell number, the larger the amount of sialylated products obtained. The optimum concentrations of primers I and II were found to be 200 and 100 microM, respectively. Above these concentrations, productivity and cell viability decreased. As regards the length of incubation time, the sialylated products increased linearly until 48 h, but productivity did not advance thereafter. These results represent the optimal conditions that are necessary for the mass production of GM3-type oligosaccharide using azidododecyl lactoside primers and B16 cells.

A novel approach to functionalization of allyl aglycon. Effective synthesis of selectively protected 2-aminoethyl lactoside, a common building block for the synthesis of carbohydrate chains of glycolipids

A novel approach to the functionalization of aglycon in allyl glycosides is described. The method comprises ozonolysis of the double bond in the allyl group, leading to the corresponding aldehyde, and subsequent transformation of the latter into the corresponding oxime, which is finally reduced to give the amine. The efficiency of this synthetic sequence (yield ∼90%) is exemplified by the transformation of two allyl lactoside derivatives into selectively protected 2-aminoethyl lactosides. The latter are convenient common building blocks for the synthesis of carbohydrate chains of glycolipids that have a lactose unit at the reducing end.

Single step syntheses of lactosylated clusters by telomerizations

N-Acryloylated lactoside derivatives containing spacer arms of different length were polymerized in the presence of thiols acting as radical scavengers to provide small oligomeric clusters (telomers) in a single step. t-Butyl mercaptan and methyl 3-mercaptopropionate chosen as chain transfer reagents, were used for further attachment to L-lysine methyl ester.

A convenient synthesis of N-acetyllactosamine derivatives from lactal

In a thermal inverse-type hetero-Diels-Alder reaction of O-protected lactal 1 and bis(2,2,2-tri-chloroethyl) azodicarboxylate ( 2), the dihydrooxadiazine derivative 3 was obtained in a very high yield; transesterification with benzyl alcohol furnished the corresponding derivative 4. Treatment of 3 with methanol in the presence of BF 3·OEt 3 afforded the methyl lactoside derivatives 5 which, after transesterification with benzyl alcohol, then hydrogenolytic debenzylation and concomitant NN-cleavage with Raney nickel, and N-acetylation, furnished methyl O-(2,4,6-tri- O- tert-butyldimethylsilyl-β- d-galactopyranosyl)-(1 → 4)-2-acetamido-3,6-di- O- tert-butyldimethylsilyl-2-deoxy-β- d-glucopyranoside ( 7) in high yield. Desilylation of 4, then O-acetylation, methyl glycoside formation with methanol-BF 3·OEt 2, hydrogenolytic debenzylation, and NN-cleavage with Raney nickel, and N-acylation afforded methyl O-(2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)-(1 → 4)-2-acetamido-3,6-di- O-acetyl-2-deoxy-β- d-glucopyranoside ( 10).

Syntheses of 6-Acetamido-6-deoxy-lactose Derivatives

A facile synthesis of lactosan hexaacetate (2) was described. 6-Acetamido-6-deoxylactose (9) was synthesized starting from 2 via hepta-O-acetyl-6-O-methylsulfonyl-β-lactose (3), benzyl hexa-O-acetyl-6-O-methylsulfonyl-fl-lactoside (4), and benzyl hexa-O-acetyl-6-azido-6-deoxy-il-lactoside (6), followed by catalytic reduction of compound (6), successive acetylation and deacetylation. Compound (9) did not show antibacterial activity against twenty microorganisms.Methyl 6-acetamido-6-deoxy-β-lactoside (14) was also synthesized using the analogous synthetic route. Syntheses and properties of seven new lactose or lactoside derivatives were also described.