Peter Köll

Thermal degradation of chitin and cellulose

Abstract Dry chitin was thermally degraded under nitrogen. The main volatile degradation product was acetamide. Chitin and cellulose were depolymerized by thermal degradation in tetraethyleneglycol dimethylether as a high boiling and inert solvent to give water-soluble oligomers with a terminal anhydrosugar unit. In supercritical acetone, cellulose could be degraded to the extent of 98% and chitin to the extent of 85%. Monomeric anhydrosugars were formed with good yields and could be identified and isolated from the degradation syrups.

Substrate specificity of sheep liver sorbitol dehydrogenase

The substrate specificity of sheep liver sorbitol dehydrogenase has been studied by steady-state kinetics over the range pH 7-10. Sorbitol dehydrogenase stereo-selectively catalyses the reversible NAD-linked oxidation of various polyols and other secondary alcohols into their corresponding ketones. The kinetic constants are given for various novel polyol substrates, including L-glucitol, L-mannitol, L-altritol, D-altritol, D-iditol and eight heptitols, as well as for many aliphatic and aromatic alcohols. The maximum velocities (kcat) and the substrate specificity-constants (kcat/Km) are positively correlated with increasing pH. The enzyme-catalysed reactions occur by a compulsory ordered kinetic mechanism with the coenzyme as the first, or leading, substrate. With many substrates, the rate-limiting step for the overall reaction is the enzyme-NADH product dissociation. However, with several substrates there is a transition to a mechanism with partial rate-limitation at the ternary complex level, especially at low pH. The kinetic data enable the elucidation of new empirical rules for the substrate specificity of sorbitol dehydrogenase. The specificity-constants for polyol oxidation vary as a function of substrate configuration with D-xylo> D-ribo > L-xylo > D-lyxo approximately L-arabino > D-arabino > L-lyxo. Catalytic activity with a polyol or an aromatic substrate and various 1-deoxy derivatives thereof varies with -CH2OH > -CH2NH2 > -CH2OCH3 approximately -CH3. The presence of a hydroxyl group at each of the remaining chiral centres of a polyol, apart from the reactive C2, is also nonessential for productive ternary complex formation and catalysis. A predominantly nonpolar enzymic epitope appears to constitute an important structural determinant for the substrate specificity of sorbitol dehydrogenase. The existence of two distinct substrate binding regions in the enzyme active site, along with that of the catalytic zinc, is suggested to account for the lack of stereospecificity at C2 in some polyols.

Transformation of aldoses into glycosylamine 1,2-(cyclic carbamates) (glyco-oxazolidin-2-ones) by reaction with potassium cyanate

Abstract Treatment of pentoses and some hexoses with potassium cyanate in aqueous solutions, buffered with sodium dihydrogen phosphate or ammonium chloride, gave glycosylamine 1,2-(cyclic carbamates) {glycofurano(or pyrano)[1,2-d]oxazolidin-2-ones}. Most of the products had furanoid structures, but d -mannose and d -lyxose gave preponderantly pyranose derivatives. Epimerisation at C-2 was observed in certain reactions. The products and their acetylated derivatives were characterised by 1H- and 13C-n.m.r. spectroscopy.

Studies of the synthesis of 1,2-cis-(cyclic carbamates) of α-d-aldopyranosylamines

Abstract Reaction of α- d -glucopyranosyl azide with triphenylphosphine and carbon dioxide gave 1- N ,2- O -carbonyl-α- d -glycopyranosylamine ( 7 ) and its α- d -furanose analogue ( 1 ), and 1- N ,3- O -carbonyl-α- d -allofuranosylamine ( 15 ) and its α- d -pyranose analogue ( 17 ). Similarly, α- d -xylopyranosyl azide gave 1- N ,2- O -carbonyl-α- d -xylopyranosylamine ( 9 ) and its α- d -furanose analogue ( 3 ), and 1- N ,3- O -carbonyl-α- d -ribopyranosylamine ( 19 ) and its β- d -xylopyranose analogue ( 21 ). The structures of the products and their acetylated derivatives were established by 1 H and 13 C NMR spectroscopy. 1- N ,3- O -Carbonyl-β- d -xylopyranosylamine ( 21 ) was obtained from β- d -xylopyranosyl azide when spontaneous rearrangement of the 1,2-(cyclic carbamate) 5 into 21 occurred in water.

Synthesis of a new chiral oxazolidinone auxiliary based on d-xylose and its application to the Staudinger reaction

Abstract The synthesis of a new chiral oxazolidinone auxiliary based on d -xylose is described which is employed in diastereoselective Staudinger-type β-lactam syntheses. Using 2-chloro-1-methylpyridinium iodide as the dehydrating reagent, the reaction of auxiliary tethered acetic acid with acyclic or cyclic imines gave the desired β-lactams in good yields with excellent cis- or trans-selectivity depending on the geometry of the imine. X-Ray structure determination of one of the obtained compounds corroborated the absolute configuration for all cis products.

Resolution of racemic carboxylic and sulfonic acids via D-xylose derived new cyclic carbamate reagents (oxazolidin-2-ones)

Abstract Two new chiral oxazolidin-2-ones have been easily prepared from D-xylose and studied as chiral derivatizing agents (CDAs) for the resolution of racemic carboxylic and sulfonic acids. The resultant diastereomers are readily separated by chromatographic methods and easily hydrolyzed to isolate the resolved materials in high optical purities and to return the CDAs for reuse.

Comprehensive Reinvestigation of The Reaction of D-Aldoses With Meldrum'S Acid Yielding Mainly Chain Extended 3,6-Anhydro-2-Deoxy-Aldono-1,4-Lactones

ABSTRACT All diastereomeric aldo-D-pentoses and -D-hexoses were reacted with Meldrums acid (2,2-dimethyl-1,3-dioxane-4,6-dione) under basic conditions. A protocol was applied and optimized which was originally reported by J. A. Galbis Perez et al. in 1990. In every case formal substitution of the anomeric hydroxyl against a carboxy-methylene group occurred thus elongating the carbon chain of the parent aldose by a C2 fragment. Products are mainly 3,6-anhydro-2-deoxy-aldono-1,4-lactones in which the lactone rings are annulated to a furanoid system. However, D-mannose and D-lyxose also gave pyranoid 3,7-anhydro-1,4-lactones. Intermediates are unsaturated open-chain 1,4-lactones (butenolides) which in some cases could be isolated as by-products. Epimerisation at C-2 of the parent aldose occurred at least partially in most reactions. The products and their acetylated derivatives were characterized by 1H and 13C NMR spectroscopy. A proposed mechanism of this reaction is supported by additional experimental evidence.

Kristall- und Molekülstruktur von d-Altritol (“d-Talitol”)

Abstract The crystal structure of d -altritol (C 6 H 14 O 6 ; space group P 2 1 ) was resolved to final residual factors of R 0.054 and R w 0.032 by direct methods. The molecules showed a sickle conformation in which a parallel 1,3-interaction (C//O) between C-6 and O-3 is tolerated, thus avoiding a parallel interaction (O//O) between O-3 and O-5 in an extended, planar, zig-zag conformation. Surprisingly, a sickle conformation avoiding all such interactions, and which was predicted earlier, was not observed.

Syntheses of 2,6-anhydroaldonic acids from the corresponding anhydrodeoxynitroalditols (glycopyranosylnitromethanes) and their conversion into methyl esters, amides, and alditols

Abstract 2,6-Anhydroaldonic acids were obtained by oxidation of the corresponding anhydrodeoxynitroalditols (glycopyranosylnitromethanes) with hydrogen peroxide in alkaline solution. Purification was achieved via the methyl anhydroaldonates. The syntheses of five 2,6-anhydrohexonic and eight 2,6-anhydroheptonic acids were accomplished in yields of 44–81%. All corresponding unprotected and acetylated methyl 2,6-anhydroaldonates were characterised. Ammonolysis of the former afforded the corresponding amides in quantitative yields; reduction with sodium borohydride gave the analogous anhydroalditols.

D-xylose derived oxazolidin-2-ones as chiral auxiliaries in stereoselective acylations and halogenations

Abstract Chiral N-acylated oxazolidin-2-ones readily available from D-xylose have been demonstrated to undergo highly diastereoselective acylation reactions via their lithium imide enolates to afford β-keto imides. These are easily purified and exhibit surprisingly high stability towards epimerization. The glyco-oxazolidin-2-ones can also be used in diastereoselective halogenation reactions via their boron enolates to get α-halogenated products. These and the branched N-acyl compounds can be hydrolyzed allowing isolation of the desired halogenated and ramified carboxylic acids and return of the auxiliaries for reuse.