Sugar chemistry without protecting groups-III. A facile chemical synthesis of 6-O-acyl-D-glycopyranoses and methyl-6-O-acyl-d-glycopyranosides

Antibacterial and Antifungal Activity of Three Monosaccharide Monomyristate Derivatives

Microbial infections remains a serious challenge in food industries due to their resistance to some of the well-known antibacterial and antifungal agents. In this work, a novel monomyristoyl ester (fructosyl monomyristate) and two other derivatives (i.e., glucosyl and galactosyl monomyristates) were successfully synthesized from myristic acid and monosaccharides in two-step reactions. First, the myristic acid was converted to myristoyl chloride, and then the myristoyl chloride was reacted with fructose, glucose and galactose separately to produce the corresponding monosaccharide monomyristate derivatives. The structures of the synthesized products were confirmed by Fourier transform infrared (FTIR), proton and carbon nuclear magnetic resonance (¹H- and ¹³C-NMR), and mass spectral (MS) data. The monomyristates esters were obtained in reaction yields of 45.80%-79.49%. The esters were then evaluated for their antimicrobial activity using the disc diffusion test. It was found that the esters exhibited a medium antibacterial activity against gram-positive bacteria; however, they showed a weak antibacterial activity against gram-negative bacteria. Amongst the esters, galactosyl myristate yielded the highest antibacterial activity against Salmonella typhimurium, Staphylococcus aureus and Bacillus subtilis, while glucosyl monomyristate exhibited the highest antibacterial activity only against Escherichia coli. Additionally, all products showed remarkable antifungal activity against Candida albicans. These findings demonstrate that monosaccharide monomyristate derivatives are promising for use as biocompatible antimicrobial agents in the future.

Regioselective formation of 6-O-acylsucroses and 6,3′-di-O-acylsucroses via the stannylene acetal method

Regioselective formation of 6-O-acylsucroses and 6,3'-di-O-acylsucroses in one pot with good yields was achieved for the first time by a typical acylation method of sucrose via its dibutylstannylene acetal. Pure monoesters at OH-6 and diesters at OH-6,3' obtained by these procedures were readily isolated by simple column chromatography, thus overcoming the main difficulties associated with regioselectivity, efficiency, and isolation techniques for the practical preparation. Explanations for the regioselectivities observed during this stannylene acetal-mediated reaction were also proposed based on the structures of the stannylene acetal in solution and the intramolecular migration of stannylenes.

1,5-Anhydro-D-fructose; a versatile chiral building block: biochemistry and chemistry

There is a steadily increasing need to expand sustainable resources, and carbohydrates are anticipated to play an important role in this respect, both for bulk and fine chemical preparation. The enzyme alpha-(1-->4)-glucan lyase degrades starch to 1,5-anhydro-D-fructose. This compound, which has three different functional properties, a prochiral center together with a permanent pyran ring, renders it a potential chiral building block for the synthesis of valuable and potentially biologically active compounds. 1,5-Anhydro-D-fructose is found in natural materials as a degradation product of alpha-(1-->4)-glucans. The occurrence of lyases and the metabolism of 1,5-anhydro-D-fructose are reviewed in the biological part of this article. In the chemical part, the elucidated structure of 1,5-anhydro-D-fructose will be presented together with simple stereoselective conversions into hydroxy/amino 1,5-anhydro hexitols and a nojirimycin analogue. Synthesis of 6-O-acylated derivatives of 1,5-anhydro-D-fructose substituted with long fatty acid residues is carried out using commercially available enzymes. Those reactions lead to compounds with potential emulsifying properties. The use of protected derivatives of 1,5-anhydro-D-fructose for the synthesis of natural products is likewise reviewed. The potential utilization of this chemical building block is far from being exhausted. Since 1,5-anhydro-D-fructose now is accessible in larger amounts through a simple-enzyme catalyzed degradation of starch by alpha-(1-->4)-glucan lyase, the application of 1,5-anhydro-D-fructose may be considered a valuable contribution to the utilization of carbohydrates as the most abundant resource of sustainable raw materials.

New biocompatible cationic amphiphiles derivative from glycine betaine: a novel family of efficient nonviral gene transfer agents

With the aim of developing new efficient agents for transfecting of eukaryotic cells we have designed and synthesized a novel family of cationic lipid vectors derived from glycine betaine. In this study we present three novel molecules differing by the length of their aliphatic chains (R=12,R=14,R=16). The lyotropic properties of these cationic lipids have been determined, and their transfection efficiency on different cell lines evaluated, using a luminescent assay. Two of these compounds, GB14 and GB12 are efficient in vitro experiments. Cytoxicity evaluation of these new molecules showed promising results with a low cytotoxicity, especially when co-lipids were included in the formulation. These compounds represent a new family of gene transfer vectors which display good transfection efficiency and low toxicity, possibly due to the natural properties of glycine betaine. These compounds have great potential for the future development of in vivo gene transfer protocols.

Nonionic surfactants regioselective synthesis of fatty acid esters of alpha- and beta-glucopyranose

Lipophilic esters of saccharides belong to the family of nonionic surfactants widely employed in pharmaceutical and cosmetics formulations. A very simple method is presented whereby 6-O-esters of alpha- and beta-glucose can be prepared and isolated. Good results have been obtained in the synthesis of 6-O-oleyl derivatives by simple acylation with appropriate oleyl chloride. The condensing agent bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOP-Cl) allows the preparations of the same esters with better regioselectivity but with yields strongly dependent on the aliphatic chain length of the carboxylic acids employed.

Tin(IV)-functionalised polymer supports; non-toxic and practical reagents for regioselective acetylation of sucrose

Polymer-supported butyltin(IV) reagents have been surveyed for regioselectivity in acetylation of sucrose. Polymer-supported butyltin(IV) dichloride 8 catalysed the acetylation of sucrose to give a 59% yield of 6-O-acetyl sucrose 3, the precursor of sucralose. The yield is close to that of a previously reported process involving dibutyltin(IV) oxide (Bu2SnO). The spent polymeric resin could readily be regenerated and can be subsequently used in further synthetic reactions.

A new synthesis of 6-O-acylsucroses and of mixed 6,6'-di-O-acylsucroses

Various 6-O-acylsucroses were synthesized in good yields from unprotected sucrose in N,N-dimethylformamide and the appropriate 3-acylthiazolidine-2-thiones 6 or 3-acyl-5-methyl-1,3,4-thiadiazole-2(3H)-thiones 7. A selective ionization of the free sugar by sodium hydride or triethylamine, followed by acylation with 6, gave 2-O-acylsucroses which were subjected in situ to intramolecular isomerizations using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or an aqueous solution of triethylamine to yield 6-O-acylsucroses. The later were otherwise obtained directly when sucrose was acylated with 6 or 7 in the presence of DBU. Moreover, mixed 6,6'-di-O-acylsucroses were readily obtained from 6'-monoacylates by using a Mitsunobu reaction without involving the concomitant formation of the 3',4'-epoxide.