Daniel Anker

Performance of Selected Microbial Pectinases on Synthetic Monomethyl-esterified Di- and Trigalacturonates

Two monomethyl esters of α-(1–4)-linked d-galacturonic dimers and three monomethyl esters of α-(1–4)-linked d-galacturonic acid trimers were synthesized chemically and further used as substrates in order to establish the substrate specificity of six different endopolygalacturonases from Aspergillus niger, one exopolygalacturonase from Aspergillus tubingensis, and four selected Erwinia chrysanthemi pectinases; exopolygalacturonan hydrolase X (PehX), exopolygalacturonate lyase X (PelX), exopectate lyase W (PelW), and oligogalacturonan lyase (Ogl). All A. niger endopolygalacturonases (PGs) were unable to hydrolyze the two monomethyldigalacturonates and 2-methyltrigalacturonate, whereas 1-methyltrigalacturonate was only cleaved by PGI, PGII, and PGB albeit at an extremely low rate. The hydrolysis of 3-methyltrigalacturonate into 2-methyldigalacturonate and galacturonate by all endopolygalacturonases demonstrates that these enzymes can accommodate a methylgalacturonate at subsite −2. TheA. tubingensis exopolygalacturonase hydrolyzed the monomethyl-esterified digalacturonates and trigalacturonates although at lower rates than for the corresponding oligogalacturonates. 1-Methyltrigalacturonate was hydrolyzed at the same rate as trigalacturonate which demonstrates that the presence of a methyl ester at the third galacturonic acid from the nonreducing end does not have any effect on the performance of exopolygalacturonase. Of the fourE. chrysanthemi pectinases, Ogl was the only enzyme able to cleave digalacturonate, whereas all four enzymes cleaved trigalacturonate. Ogl does not cleave monomethyl-esterified digalacturonate and trigalacturonate in case the second galacturonic acid residue from the reducing end is methyl-esterified. PehX did not hydrolyze any of the monomethyl-esterified trigalacturonates. The two lyases, PelX and PelW, were both only able to cleave 1-methyltrigalacturonate into Δ4,5-unsaturated 1-methyldigalacturonate and galacturonate.

Phenylselenofluoration d'alcynes

Abstract The electrophilic anti-addition of the elements of benzeneselenenyl fluoride towards carbone-carbone triple bonds is performed by a one-pot reaction of N-phenylselenophthalimide and triethylamine tris-hydrofluoride with disubstituted alkynes ; starting from monosubstituted alkynes, the reaction proceeds further to afford vinylic diselenated compounds after hydrofluoric acid elimination. Some products of mono-addition could be transformed into vinylic or allenic fluorides.

Phenylselenofluoration d'alcenes acido-sensibles

Abstract β-phenylselenofluorides have been synthesized by reaction of olefins (even acido-sensitive ones) with N-phenylselenophtalimide in the presence of triethylamine tris-hydrofluoride. Owing to the regioselectivity observed, this reaction constitutes a good method for functionalisation of α,β unsaturated acetals.

Synthese D′ α,β aminofluorodesoxypyranosides de methyle

Abstract Methyl α,β aminofluorodeoxypyranosids are synthesized in three steps from N,N-diallylaminosugars : O-methanesulfonylation followed with treatment by Et 3 N, 3HF leads to a fluorinated compound ; N,N-dideallylation gives the expected product.

Formal addition of methanesulfenyl fluoride to unsaturated substrates

Summary The electrophilic anti -addition of the elements of methanesulfenyl fluoride towards carbon-carbon double bonds by a one pot reaction of dimethyl(methylthio)sulfonium fluoroborate and triethylamine tris-hydrofluoride with various types of alkenes is used for the synthesis of β-fluoroalkyl-methylthioethers.

Trifluoromethylation of sugar 1,4-lactones : Synthesis of 5-deoxy-5,5,5-trifluoro-D and L-ribose and lyxose derivatives

Abstract The four 5-deoxy-5,5,5-trifluoro-D and L-ribo and -lyxo furanoses were synthesized from lactones using CF 3 SiMe 3 in 5 or 6 steps and 30–40 % overall yield. The key step was a stereoselective reduction of 1,1,1-trifluoro-2-ketoses with LiAlH 4 or NaBH 4 at an anomeric centre.

Stéréosélectivité comparée de la réduction de trifluorométhylcétones et des méthylcétones correspondantes: nouvelles voies d'accès à des dérivés trifluorométhylés de pentoses

Abstract The selectivity of the reduction of some trifluoroacetyl-1,3-dioxanes and 1,3-dioxolanes with DIBAH or L-Selectride was studied and compared with that of the corresponding methylketones; the results -in accordance with literature- show an important steric hindrance of the CF 3 group. The selectivity observed in these reductions led to good yields in the syntheses of 5,5,5-trifluorinated derivatives of D and L-pentofuranoses; a new method for the preparation of some functionalized trifluoromethylketones is described.

Nouvelle synthese de l'acide 3-desoxy-D-erythro-2-hexulosonique (KDG). A partir de la D-glucono-1,5-lactone synthese et étude de RMN de derives O-methyles du KDG

ABSTRACT 3-Deoxy-D-erythro-2-hexulosonic acid (KDG), an important metabolite of bacterial polysaccharide degradation, was prepared from D-glucono-1,5-lactone through a six-step sequence, with a 45% overall yield. Using suitable intermediates. KDG methyl ester and its 5- and 6-O-methylated derivatives were also synthesized. 1H and 13C NMR studies of 5- and 6-O-methylated derivatives (pyranoid and furanoid forms respectively) compared to those of KDG and its methyl ester allowed us to conclude that these two latter compounds exist in equilibrium as forms whose percentages were determined.

Nouvelle Synthese De L'Acide 3-Desoxy-D-Erythro-2-Hexulosonique (KDG) A Partir Du D-Glucose

ABSTRACT 3-Deoxy-D-erythro-2-hexulosonic acid (KDG), an important metabolite of bacterial polysaccharides degradation was prepared from D-glucose in six steps via the synthesis of 2,4-O-isopropylidene-D-erythrose and subsequent Wittig-Horner condensation followed by smooth deprotections of protecting groups. Overall yield was 35% from D-glucose.

SYNTHESE DES 5-DESOXY-5,5,5-TRIFLUORO-D- ET -L-PENTOFURANOSES

ABSTRACT Synthetic pathways leading to 5-deoxy-5,5,5-trifluoropentofuranoses are reported. The main difficulty was to obtain a good diastereoselectivity at the C-4 carbon bearing the CF3 group. For the ribose and the lyxose derivatives the problem was partially solved by reacting trifluoromethyltrimethylsilane with 1,4-lactones of suitable glyconic acids leading to hemiketalic 1-deoxy-1,1,1-trifluoro-2-ketoses. Reduction of these ketoses with NaBH4 or LiA1H4 allowed the desired configuration at the C-4 carbon. For the arabinose and the xylose derivatives it was found more convenient to synthesize uncyclised 1-deoxy-1,1,1-trifluoro-2-ketopentoses by Dess-Martin oxidation of the corresponding protected alcohols. Highly selective reductions of these trifluoromethylketones led to arabino or xylo derivatives depending on the reducing agent.