Thomas T. Stevenson

Some reactions of levoglucosenone

Abstract The role of the major variables in the pyrolytic production of levoglucosenone from acid-treated cellulose and paper has been established. Reduction, oxidation, acid- and base-catalyzed addition, acetolysis, and rearrangement reactions of this product have been investigated. These reactions proceed with considerable stereo-selectivity to give a variety of novel compounds. Nucleophilic addition to the double bond provides a facile method for the synthesis of 4-thio and other 4-substituted sugar derivatives.

Influence of linkage position and orientation in pyrolysis of polysaccharides: A study of several glucans☆

Abstract Six naturally occurring and three synthetic glucans have been studied. The natural glucans contain 1,3-, 1,4- and 1,6- linkages with α- and β-orientations, while the synthetic glucans contain all possible linkage positions and orientations and also varying proportions of pyranose and furanose forms. The volatile products of pyrolysis are very dependent on the presence of trace amounts of inorganic-contaminants, which were detected as metal ions in all of the natural glucans. For most glucans these contaminants were effectively removed by washing with dilute acid. This removal of contaminants was, however, incomplete in the cases of amylose and of laminaran. The glucans, after purification in this way, all gave very similar pyrolytic yields of levoglucosan (LG), showing that LG formation is not dependent on polysaccharide linkage position or orientation, and thus confirming a recent hypothesis for mechanism of LG formation. The presence during pyrolysis of inorganic compounds (either indigenous or added), always led to decrease in LG and increase in yield of formic and acetic acids, glycolaldehyde, hydroxyacetone and phenols, thus indicating that the mechanism of formation of such compounds is also not dependent on polysaccharide linkage position or orientation.

1,5-Anhydro-4-deoxy-d-glycero-hex-1-en-3-ulose and other pyrolysis products of cellulose

Abstract Uncatalyzed pyrolysis of cellulose provides a tar containing mainly 1,6-anhydro- d -glucose derivatives and some unsaturated products. The latter include a new enone that has been isolated by preparative column chromatography in 1.4% yield and identified as 1,5-anhydro-4-deoxy- d - glycero -hex-l-en-3-ulose. This compound is also formed by pyrolysis of other carbohydrate polymers. A mechanism for its production from internal units has been deduced from the experimental data. The pyrolysis products of cellulose also contain 3,5-dihydroxy-2-methyl-4 H -pyran-4-one, which appears to be an oxidation product.

Identification of an agar constituent responsible for hydric control in micropropagation of radiata pine

Tissue cultured Pinus radiata grown on media containing agar as the gelling agent display toxic symptoms and poor long-term shoot survival, however it does have the attribute of hydric control, through a mechanism which, until now, has not been elucidated. Gelrite as an alternative gelling agent is clearly non-toxic but results in hyperhydric (vitrified) tissues. In an effort to overcome these problems, the controlling mechanism found in agar was examined. Hydric control was shown to be effected by a non-gelling, cold-water soluble constituent of a commercial agar, rather than by physical properties of the gel. It could be separated from low molecular weight components of the agar responsible for the toxic symptoms by dialysis. It was identified as being an agaroid-type xylogalactan bearing pyruvate and sulphate substituents. Improved management of gelling agents in culture medium has contributed substantially to a thirty fold increase in propagation rates.

Acid-catalyzed pyrolytic synthesis and decomposition of 1,4:3,6-dianhydro-α-d-glucopyranose

Abstract 1,4:3,6-dianhydro-α- d -glucopyranose (1) was formed, together with 1,6-anhydro-3,4-dideoxy-β- d -glycero-hex-3-enopyranos-2-ulose (levoglycosenone, 2) and levoglucosan (4), on acid-catalyzed pyrolysis of d -glucose, amylopectin, and cellulose. Pyrolysis of 1 in the presence of acid provided significant quantities of 2, indicating that 1 can act as a pyrolytic precursor of 2. A pyrolysis product from cellulose previously considered to be 1,6-anhydro-3-deoxy-β- d -erythro-hex-3-enopyranose (12) was shown to be dianhydride 1.

Synthesis and thermal chemistry of isolevoglucosenone

Abstract Isolevoglucosenone (1,6-anhydro-2,3-dideoxy-β- d - glycero -hex-2-enopyranos-4-ulose, 3 ) has been synthesized from levoglucosenone ( 2 ) in six steps. Thus, 1,6-anhydro-4- O -benzyl-3-deoxy-β- d - erythro -hexopyranos-2-ulose, obtained by Michael addition of benzyl alcohol to 2 , was reduced with sodium borohydride to yield a separable mixture of the C-2 epimeric alcohols 1,6-anhydro-4- O -benzyl-3-deoxy-β- d - arabino - and - ribo -hexopyranose, both of which displayed intramolecular hydrogen-bonding. Acetylation, hydrogenolytic debenzylation, and pyridinium chlorochromate oxidation then led to the 2- O -acetyl-1,6-anhydro-hexos-4-uloses, from which 3 was obtained by tetraethylammonium acetate-catalyzed β-elimination of acetic acid. On sealed-tube thermolysis in the range of 210–260°, 3 generated 3-oxidopyrylium by loss of formaldehyde; this ylide was efficiently trapped by unreacted 3 , to yield the [4 π + 2 π ]-1,3-dipolar cycloadducts 14 and 15 . The structure of 14 was fully elucidated by an X-ray crystallographic study. Neither 3 was, nor the adducts 14 and 15 were, detected among the products from acid-catalyzed pyrolysis of cellulose.

Agaroids from New Zealand members of the Gracilariaceae (Gracilariales, Rhodophyta) — a novel dimethylated agar

Polysaccharide extracts from four New Zealand members of the Gracilariaceae have been characterized by 13C-NMR spectroscopy and GLC analysis of alditol acetate derivatives prepared using a new double hydrolysis-reduction procedure. All were based on variously substituted repeating disaccharide units of agarobiose and ≤ 20% of its ‘precursor’ containing l-galactose-6-sulfate. Gracilaria truncata yielded a firm gelling agar with 67% methylation on the 6-position of the d-galactose residues. The other extracts belong to a new class of agar molecules having methylation on both the 6-position of the d-galactose units and the 2-position of the l-sugar units. The Curdiea coriacea polysaccharide displayed this double methylation almost completely (≥ 96 %); the alkali-modified polymer thus had only two free hydroxy-groups per disaccharide repeat unit, yet still gave a firm gel. The Curdiea flabellata and Melanthalia abscissa extracts had this double methylation pattern but to a lesser extent, and additional xylosyl branch units on up to 18% of the repeating disaccharide units.

Base-catalyzed oligomerization of levoglucosenone

Abstract Heating levoglucosenone in aqueous triethylamine gives a dimer and two trimers in yields of 8, 18, and 56%, respectively. These compounds have been isolated crystalline, and their structures and stereochemistry have been investigated by 13 C- and 1 H-n.m.r. and other spectroscopic methods. These data indicate that the dimer is apparently formed by Michael addition to provide a C-3-C-4 linkage. Similar reactions provide a non-olefinic, C-3-C-4-linked, cyclic trimer and an olefinic, cyclic trimer containing two C-3-C-4 linkages and one C-2-C-3 linkage.

The xylogalactan sulfate from Chondria macrocarpa (Ceramiales, Rhodophyta)

A structure is proposed for the complex xylogalactan sulfate from Chondria macrocarpa. The hot-water extract of C. macrocarpa was desulfated or alkali-treated and Smith degraded. Constituent sugars and their substitution patterns were identified using a modified Hakamori methylation procedure suited to sulfated polysaccharides and a double hydrolysis-reduction protocol that yielded derivatives from all of the sugar residues, including the labile 3,6-anhydrogalactosyl residues. The polymer has an agar-type backbone of alternating 3-linked \-d- and 4-linked α-L-galactopyranosyl units. The d-residues are partially sulfated on O-2 (50%) and O-6 (20–30%). About 40% of the l-residues are present as the 3,6-anhydride and 25% as its ‘precursor’ l-galactose 6-sulfate. A significant proportion of the remaining l-galactosyl residues have both a d-xylopyranosyl substituent on O-3 and a sulfate ester on O-6 and are stable to alkali.

Thermal polymerization of some glucofuranose derivatives

Methyl alpha,beta-D-glucofuranoside (1) and 1,2-O-isopropylidene-alpha-D-glucofuranose (2) have been polymerized thermally, using 0.1% phosphoric acid as catalyst. The resulting alcohol-insoluble polymers were analyzed by gel-permeation chromatography and methylation analysis. The two starting materials gave polymers that were very similar in molecular-weight distribution and in glycosyl-linkage composition. The proportion of furanosyl residues in the polymer, estimated by the relative proportions of furanosyl and pyranosyl residues that could be determined unequivocally by methylation analysis, was approximately 35-40%; higher than is found when glucopyranosides are polymerized, but indicating that significant furanose-pyranose isomerization had occurred during the polymerization process.