Joachim Thiem

Glycosylation employing bio-systems: from enzymes to whole cells

This contribution will highlight chemoenzymatic approaches to the rather complex task of stereospecific and regiospecific glycosylation. Advantages and problems associated with the application of enzymes from carbohydrate metabolism as organic reagents in aqueous and non-aqueous solvent systems are discussed. One chapter will report on the use of glycosidases in reverse hydrolysis and tranglycosylation reactions. Another section focuses on the syntheses with simple as well as more complex and delicate glycosyl-transferases including cofactor regeneration. Further, effective combination of both degrading and synthesising enzyme systems, and finally glycosylations employing cells with direct access to their complete enzyme equipment are treated.

Studies on liquid-crystalline glycosides

Abstract A number of α- and β-glycosides with long chain aliphatic alcohols as aglycones were prepared, and the liquid-crystalline properties of the various mono-, di, and trisaccharide series compared. Further, the first liquid-crystalline glycosides of glucuronic acid and of an amino sugar hydrochloride were detected. It may be concluded that the clearing points increase with (a) a larger number of hydrogen bonds, (b) a rope-like, space-filling structure, and (c) a balanced molecular weight ratio between the polar and apolar parts of the molecule. In all of the cases studied so far only smectic A phases were observed.

Aufbau von Oligosacchariden mit Glycosylfluoriden unter Lewissaüre-katalyse

Abstract Glycosylation of 1,2:3,4-di-O-isopropylidene-α- d -galactopyranose (6), as well as its 6-trimethylsilyl ether 7 with 2,3,4,6-tetra-O-acetyl-β- d -glucopyranosyl fluoride (5) was achieved stereospecifically in a mild and fast manner in the presence of Lewis acids like, e.g., titanium tetrafluoride, to give the β-(1→6)-linked disaccharide derivative 1. By use of 2,3,4,6-tetra-O-benzyl-β- d -glucopyranosyl fluoride (8) or its α anomer 10 and titanium tetrafluoride in acetonitrile with 6 or 7, a fast reaction proceeds preponderantly to yield 1,2:3,4-di-O-isopropylidene 6-O-(2,3,4,6-tetra-O-benzyl-β- d -glucopyranosyl)-α- d -galactopyranose (2). In ether, however, mainly the α-(1→6) anomer was formed. These model systems were used to elucidate the limiting conditions for this procedure, and mechanistic conceptions are discussed. By glycosylation at O-4 of 1,6:2,3-dianhydro-β- d -mannopyranose (11) with the perbenzylated α-fluoride 10 both the α- and the β- d -(1→4) disaccharide derivatives 12 and 14 were obtained, but 5 gave exclusively the β- d -(1→4) compound 16. Opening of the anhydro rings of 12 led to the synthesis of N-acetyl-maltosamine (22). 1,6-Anhydro-2-azido-4-O-benzyl-2-deoxy-β- d -glucopyranose was glycosylated with methyl (2,3,4-tri-O-acetyl-β- d -galactopyranosyl fluoride)uronate under titanium tetrafluoride catalysis to give the β- d -(1→3)-linked disaccharide 16, subsequently transformed into 29.

Synthesis of polyterephthalates derived from dianhydrohexitols

SummaryBy melting condensation of terephthalic acid dichloride and 1,4∶3,6-dianhydrohexitols as well as selectively prepared lower oligomers thereof the formation of polyterephthalates is achieved. These polyesters are characterized by 1H-NMR spectra vapour pressure osmometry (VPO), differential scanning calorimetry (DSC), viscosity measurements and combustion analyses. Their preparation and properties are discussed.

Synthesis of a novel starch‐derived AB‐type polyurethane

Starting from 1,4:3,6-dianhydrosorbitol, a five step monomer synthesis led to 2-deoxy-1,4:3,6-dianhydro-2-isocyanato-L-iditol which by catalytic polyaddition gave a semicrystalline polyurethan with a T g of 118°C and a melting range of 190-200°C. A second route required the synthesis of 2-azido-5-O-chloroformyl-2-deoxy-1,4:3,6-dianhydro-L-iditol. During catalytic hydrogenation, the intermediate 2-aminochloroformyl derivative underwent spontaneous polycondensation to give a crystalline polyurethane with a melting range of 140-180°C

Galactosylation and glucosylation by use of β-galactosidase

Abstract The transglycosylation activity of β-galactosidase derived from Aspergillus oryzae and Escherichia coli , respectively, was examined in reaction systems containing up to 50% acetonitrile. Starting with ortho -nitrophenyl β-galactoside ( 1 ), which functions both as donor and as acceptor. β-Gal(1-6)]β-Gal-PhNO 2 - o ( 2 ) and β-Gal(1-3)β-Gal-PhNO 2 - o ( 3 ) were obtained. Under similar conditions the enzyme from A . oryzae converts para -nitrophenyl β-glucoside ( 5 ) to β-Glc(1-2)β-Glc-PhNO 2 - p ( 6 ) and α-Glc(1-4)β-Glc-PhNO 2 - p ( 7 ). Incubation of 1 and L-serine in the presence of the A . oryzae β-galactosidase leads to β-Gal-L-Ser ( 4 ).

Synthesis of methyl (d-glycopyranosyl azide) uronates

Abstract Sodium hypochlorite oxidation catalysed by 2,2,6,6,-tetramethylpiperidine 1-oxide (TEMPO) is shown to be a mild and efficient approach to the title uronates. In the gluco, galacto, allo , and 2-acetamido-2-deoxy- gluco series, the corresponding β- or α- and β-glycosyl azides could be smoothly oxidised and alternative preparations are compared to this access.

Studies on the structure of olivomycin a and mithramycin by 1H and 13C nuclear magnetic resonance spectroscopy

Abstract Extensive 1H and 13CNMR studies confirmed the gross structure of olivomycin A except for a revision with respect to a saccharide linkage. The structure of mithramycin was elucidated similarly, resulting in a substantial revision of structure for its carbohydrate moiety including interglycosidic bonds.

Chemical synthesis of GDP-L-galactose and analogues

Abstract Succinct syntheses for l -galactose, 3-deoxy- l - xylo -hexose (3-deoxy- l -galactose), 6-deoxy- l -galactopyranose ( l -fucose) and 3,6-dideoxy- l - xylo -hexose (3,6-dideoxy- l -galactose) have been developed starting from commercially available l -galactono-1,4-lactone. l -Galactose and variants were then converted to the guanosine diphosphate derivatives, via the formation of the anomeric phosphates and coupling to guanosine monophosphate morpholidate.

Studies of Hexuronic Acid Ester Glycals and the Synthesis of 2-Deoxy-β-glycoside Precursors

Abstract The hexuronic acid methyl ester glycals with L-ribo (7), D-lyxo (9), and D-xylo configuration (11a) were synthesized and their conformations and that of the D-arabino derivative 2a were studied. Using the N-iodosuccinimide alycosylation procedure these glycals were transformed into cyclohexyl 2-deoxy-2-iodoglycosides 13 - 28 and their α/β-anomer ratios determined by 1H NMR spectrocopy. The mechanism of the N-iodosuccinimide glycosylation and the correlation between glycal conformation and glycoside configuration are discussed.