Highly Regioselective C-5 Iodination of Pyrimidine Nucleotides and Subsequent Chemoselective Sonogashira Coupling with Propargylamine

An efficient C-5 iodination of pyrimidine-5′-triphosphates and subsequent palladium-catalyzed Sonogashira coupling reaction with propargylamine is described. The iodination reaction is highly regioselective and the coupling reaction is highly chemoselective that furnishes exclusive 5-(3-aminopropargyl)-pyrimidine-5′-triphosphate in good yield with high purity (>99%).     

Lipase-catalyzed regioselective synthesis of steryl (6′-<Emphasis Type="Italic">O</Emphasis>-acyl)glucosides

The regioselective acylation of cholesteryl β-d-glucoside, at the C-6 of the glucose moiety, was achieved using microbial lipases in organic solvents. With palmitic acid as an acyl donor 81 or 63% conversions of cholesteryl glucoside to its 6′-O-palmitoyl derivative were obtained using Candida antarctica or Rhizomucor miehei enzymes, respectively. High yields (64–92%) were also obtained with fatty acids 6:0–22:0 and 16:1 (n-7). The synthesis of cholesteryl (6′-O-palmitoyl)glucoside was also achieved via transesterification, using mono-, di- and tri-palmitoylglycerols or methyl and ethyl palmitate as acyl sources. With R. miehei lipase transesterification between methyl palmitate (80 mM) and cholesteryl glucoside (1 mM) proceeded after 24 h with a nearly quantitative yield (97%).     

Comparison of the effects of acylation and amidation on the antimicrobial and antiviral properties of lactoferrin

AIMS: To compare amidation and acylation of lactoferrin (LF) from bovine milk, as a means of enhancing its antimicrobial and antiviral properties. METHODS AND RESULTS: LF was chemically modified by amidation with a 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide (EDC) in the presence of ammonium ions or by acylation with either succinic or acetic anhydride. In the test systems used, amidation substantially enhanced the activity of LF against Pseudomonas fluorescens in comparison with native LF. However, increasing the net negative charge of LF by acylation had no effect on the activity of LF against P. fluorescens, and abrogated the antimicrobial activity of LF against Bacillus subtilis and Saccharomyces cerevisiae. Increasing the net negative charges of LF by acylation eliminated its antimicrobial and antiviral effects against poliovirus and feline calicivirus (nonenveloped viruses). CONCLUSIONS: The addition of positive charges to LF via amidation enhanced antimicrobial properties in contrast to increasing the negative charges by acylation, which abolished both the antimicrobial and antiviral properties of LF. SIGNIFICANCE AND IMPACT OF THE STUDY: The effects of charge alteration of LF determined in this study provides a basis for further development of LF formulations with enhanced antimicrobial effectiveness for use in food process hygiene, veterinary and health-care applications.     

pH-imprinted lipase catalyzed synthesis of dextran fatty acid ester

The application of enzymatic catalysis for the synthesis of polysaccharide-based surfactants was investigated. The polysaccharide dextran, a neutral bacterial polysaccharide consisting of -1,6 linked glucose units, was chemically modified by the attachment of hydrophobic groups through a transesterification reaction with a vinyl decanoate. A screening of commercially available lipases and protease for the synthesis of amphiphilic polysaccharides in DMSO suggested that lipase AY from Candida rugosa modified dextran T-40 with vinyl decanoate at the highest conversion. A pH-adjustment in a phosphate buffer at pH 7.5 prior to use is crucial to make this enzyme active in DMSO. The effect of enzyme concentration and mole ratio of fatty ester to dextran T-40 on the conversion and the rate of reaction were studied. Finally, investigation of the kinetics and regioselectivity of lipase AY-catalyzed modification offer a possibility to regulate the position and the extent of hydrophobic group attached to dextran. These two properties are fundamental for controlling the physico-chemical properties of the final polymeric surfactants.     

An efficient chemoenzymatic route to methyl 4-O-benzyl-2,3-anhydro-beta-D-lyxopyranoside from methyl beta-D-xylopyranoside

Methyl 4-O-benzyl-2,3-anhydro-β-d-lyxopyranoside, an intermediate for the preparation of methyl β-d-xylopyranoside derivatives modified at C-2, was obtained in five steps in 58% yield. The synthetic sequence starts from methyl β-d-xylopyranoside through two main steps involving regioselective enzymatic acetylation and deacetylation catalyzed by lipase PS.     

Synthesis of fagopyritols A1 and B1 from D-chiro-inositol

Fagopyritol A1 (3-O-alpha-d-galactopyranosyl-d-chiro-inositol) and fagopyritol B1 (2-O-alpha-d-galactopyranosyl-d-chiro-inositol) have been synthesized by glycosylation of the diequatorial diol 1,4,5,6-tetra-O-benzoyl-d-chiro-inositol, readily obtained from d-chiro-inositol, with 2,3,4,6-tetra-O-benzyl-d-galactopyranosyl trichloroacetimidate.     

SAM recognition and conformational switching mechanism in the Bacillus subtilis yitJ S box/SAM-I riboswitch

S-box (SAM-I) riboswitches are a widespread class of riboswitches involved in the regulation of sulfur metabolism in Gram-positive bacteria. We report here the 3.0-Å crystal structure of the aptamer domain of the Bacillus subtilis yitJ S-box (SAM-I) riboswitch bound to S-adenosyl-l-methionine (SAM). The RNA folds into two sets of helical stacks spatially arranged by tertiary interactions including a K-turn and a pseudoknot at a four-way junction. The tertiary structure is further stabilized by metal coordination, extensive ribose zipper interactions, and SAM-mediated tertiary interactions. Despite structural differences in the peripheral regions, the SAM-binding core of the B. subtilis yitJ riboswitch is virtually superimposable with the previously determined Thermoanaerobacter tengcongensis yitJ riboswitch structure, suggesting that a highly conserved ligand-recognition mechanism is utilized by all S-box riboswitches. SHAPE (selective 2′-hydroxyl acylation analyzed by primer extension) chemical probing analysis further revealed that the alternative base-pairing element in the expression platform controls the conformational switching process. In the absence of SAM, the apo yitJ aptamer domain folds predominantly into a pre-binding conformation that resembles, but is not identical with, the SAM-bound state. We propose that SAM enters the ligand-binding site through the “J1/2-J3/4” gate and “locks” down the SAM-bound conformation through an induced-fit mechanism. Temperature-dependent SHAPE revealed that the tertiary interaction-stabilized SAM-binding core is extremely stable, likely due to the cooperative RNA folding behavior. Mutational studies revealed that certain modifications in the SAM-binding region result in loss of SAM binding and constitutive termination, which suggests that these mutations lock the RNA into a form that resembles the SAM-bound form in the absence of SAM.     

Total synthesis of caminoside B, a novel antimicrobial glycolipid isolated from the marine sponge Caminus sphaeroconia

The first total synthesis of caminoside B, a novel marine antimicrobial glycolipid isolated from the marine sponge Caminus sphaeroconia, was developed. This marine small molecule inhibitor (IC₅₀ = 20 μM) targeting type III secretory pathway of bacterial pathogenesis was assembled in good yield via a ‘2+2+1’ strategy based on stereocontrolled construction of the four glycosidic linkages.     

Preparation of regioselectively feruloylated p-nitrophenyl α-l-arabinofuranosides and β-d-xylopyranosides—convenient substrates for study of feruloyl esterase specificity

p-Nitrophenyl α-l-arabinofuranoside and β-d-xylopyranoside mono-O-ferulates were prepared by 4-O-acetylferuloylation of corresponding enzymatically prepared di-O-acetates followed by deacetylation. An alternative mild acylation catalysed by zinc oxide was tested on xylopyranoside derivatives. The chemoselective methanolysis of the acetyl groups using neutral catalyst dibutyltin oxide at reflux was used as deacetylation method. Under these conditions a significant feruloyl migration was observed mainly on p-nitrophenyl 3-O-feruloyl-β-d-xylopyranoside resulting in low yields of the positional isomers. Investigation of substrate and positional specificity of different types of feruloyl esterases on the presented compounds in enzyme-coupled assays was reported previously.     

Efficient synthesis of a 6-deoxytalose tetrasaccharide related to the antigenic O-polysaccharide produced by Aggregatibacter actinomycetemcomitans serotype c

Concise synthesis of a 6-deoxy-α-l-talose tetrasaccharide, 6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp-(1→2)-6-deoxy-α-l-Talp-(1→3)-6-deoxy-α-l-Talp, the dimer of the disaccharide repeating unit of the OPS from Aggregatibacter actinomycetemcomitans serotype c, has been accomplished through suitable protecting group manipulations and stereoselective glycosylation starting from commercially available l-rhamnose. The target oligosaccharide in the form of its p-methoxyphenyl glycoside is suitable for further glycoconjugate formation via selective cleavage of this group.