Synthesis and anticoagulant activity of bioisosteric sulfonic-Acid analogues of the antithrombin-binding pentasaccharide domain of heparin.

Two pentasaccharide sulfonic acids that were related to the antithrombin-binding domain of heparin were prepared, in which two or three primary sulfate esters were replaced by sodium-sulfonatomethyl moieties. The sulfonic-acid groups were formed on a monosaccharide level and the obtained carbohydrate sulfonic-acid esters were found to be excellent donors and acceptors in the glycosylation reactions. Throughout the synthesis, the hydroxy groups to be methylated were masked in the form of acetates and the hydroxy groups to be sulfated were masked with benzyl groups. The disulfonic-acid analogue was prepared in a [2+3] block synthesis by using a trisaccharide disulfonic acid as an acceptor and a glucuronide disaccharide as a donor. For the synthesis of the pentasaccharide trisulfonic acid, a more-efficient approach, which involved elongation of the trisaccharide acceptor with a non-oxidized precursor of the glucuronic acid followed by post-glycosidation oxidation at the tetrasaccharide level and a subsequent [1+4] coupling reaction, was elaborated. In vitro evaluation of the anticoagulant activity of these new sulfonic-acid derivatives revealed that the disulfonate analogue inhibited the blood-coagulation-proteinase factor Xa with outstanding efficacy; however, the introduction of the third sulfonic-acid moiety resulted in a notable decrease in the anti-Xa activity. The difference in the biological activity of the disulfonic- and trisulfonic-acid counterparts could be explained by the different conformation of their L-iduronic-acid residues.

Synthesis of a sulfonic acid mimetic of the sulfated Lewis A pentasaccharide.

The first sulfonic acid mimetic of the sulfated Lewis A pentasaccharide in which the natural L-fucose unit is replaced by a D-arabinose ring was synthesized. Formation of the sulfonic acid moiety at a pentasaccharide level could be successfully achieved by means of introduction of an acetylthio moiety into the terminal D-galactose residue and subsequent oxidation. The equatorial arrangement of the acetylthio group linked to C-3 of the galactose ring could be obtained by double nucleophilic substitutions; efficient formation of the gulo-triflate derivatives required low-power microwave (MW) activation. Oxidation of the acetylthio group was carried out using Oxone in the presence of acetic acid.

Synthesis of disaccharide fragments of the AT-III binding domain of heparin and their sulfonatomethyl analogues.

d-Glucuronate and l-iduronate-containing disaccharides related to the antithrombin-binding domain of heparin were prepared. The carboxylic function of the uronic acid unit was formed on a disaccharide level in the case of the glucuronate, while on a monosaccharide level in the case of the iduronate derivatives. Synthesis of their sulfonic acid analogues was carried out analoguosly applying sulfonatomethyl-containing acceptors in the form of either salts or methyl esters. Significant difference could be observed in the methyl ether formation reactions of the sulfonatomethyl-containing uronate disaccharides and the non-sulfonic acid uronates.

Synthesis, regioselective hydrogenolysis, partial hydrogenation, and conformational study of dioxane and dioxolane-type (9'-anthracenyl)methylene acetals of sugars.

Dioxane-type (9'-anthracenyl)methylene acetal of methyl 2,3-di-O-methyl-alpha-D-glucopyranoside was cleaved with LiAlH(4)/AlCl(3) (3:1) or with Na(CN)BH(3)-HCl regioselectively to provide the 4- or 6-O-(9'-anthracenyl)methyl ether, respectively. Hydrogenolytic reaction of the exo and endo isomers of dioxolane-type acetals proved to be directed by the configuration of the acetalic carbon as well as by the intramolecular participation of the adjacent-free hydroxyl; ring-opening reaction of the endo isomer of the methyl 2,3-O-(9'-anthracenyl)methylene-alpha-L-rhamnopyranoside took place with complete selectivity resulting in the axial (9'-anthracenyl)methyl ether, whereas a 1:1 mixture of the axial and equatorial ethers was formed upon the same reaction of the exo isomer. Catalytic hydrogenation of the sugar acetals resulted in (9',10'-dihydro-9'-anthracenyl)methylene derivatives without affecting the acetalic center. High-temperature molecular dynamics simulations and DFT (Density Functional Theory) geometry optimizations were carried out to study the conformation of the dioxane-type (9',10'-dihydro-9'-anthracenyl)methylene acetal.

Reactions of phenyl and ethyl 2-O-sulfonyl-1-thio-alpha-D-manno- and beta-D-glucopyranosides with thionucleophiles.

Persubstituted derivatives of phenyl and ethyl 2-O-sulfonyl-1-thio-alpha-D-manno- and beta-D-glucopyranosides were synthesized and reacted either with PhSNa or with MeSNa. The phenyl-1-thio compounds afforded the dithio-1,2-cis-axial/equatorial-alpha-D-glucopyranosides or dithio-1,2-cis-equatorial/axial-beta-D-mannopyranosides by means of S(N)2 type of reactions. Starting from the ethyl-1-thio derivatives intramolecular 1,2-thio-migration took place predominantly. In the case of mannosides both nucleophilic reagents facilitate the formation of 1-SPh- or 1-SEt glycals by elimination. The formation of unsubstituted glycal could also be observed from the ethyl-1-thio derivatives, especially by using PhSNa as a nucleophile. The 1,2-dithio-glycosides are glycosyl donors affording 1,2-trans-2-thio-glycosides.

Synthesis of 3,6-branched arabinogalactan-type tetra- and hexasaccharides for characterization of monoclonal antibodies.

Synthesis of tetra- and hexasaccharides built up from a beta-(1-->6)-linked galactopyranosyl backbone with arabinofuranosyl side chains at position 3 and with a 3-aminopropyl spacer related to arabinogalactans is described. These oligosaccharides were prepared for investigation of monoclonal antibodies raised against arabinogalactan proteins (AGPs) from pressed juice of Echinacea purpurea.

Toward synthesis of the isosteric sulfonate analogues of the AT-III binding domain of heparin.

D-glucuronate and l-iduronate containing disaccharides related to the antithrombin-binding pentasaccharide of heparin, in which one of the sulfate esters is systematically replaced by a sodium sulfonatomethyl moiety, were synthesized. The sulfonic acid group was introduced by stereoselective radical addition onto the exomethylene moiety of the appropriate glycoside derivatives, and the resulting sulfonatomethyl glucosides were used as acceptors.

Combined NMR three-bond scalar coupling measurements and QM calculations to calculate OH-rotamer equilibrium of polyalcohols.

A combined but independently applied NMR and QM procedure has been used to investigate the conformational properties of the exchangeable hydroxyl protons of polyalcohols. In this study, to demonstrate the applicability of such a strategy, we investigated a simple monosaccharide, i.e. alpha- and beta-anomers of a D-glucopyranoside derivative. The redundant set of experimental vicinal homonuclear and heteronuclear scalar couplings involving the OH-protons obtained for both anomers of our model compound were simultaneously analyzed to yield the preferred OH-rotamer populations and moreover to parametrize a new Karplus-type equation for (3)J(C(i-1)OH(i)) coupling. The populations of the lowest energy conformers and the conformational-averaged coupling constants were independently calculated using the QM approach in both vacuum and chloroform. The similarity of the estimated rotamer populations obtained by two very different techniques and the similarity of the experimental and calculated coupling constants suggest that these approaches can be used in conjunction and in a fully integrated way to determine a more accurate atomic level description of molecular conformers.

Synthesis of ketopyranosyl glycosides and determination of their anomeric configuration on the basis of the three-bond carbon-proton couplings.

Anomeric pairs of ketopyranosyl glycosides with various substituents at C(alpha), C(beta) and C(gamma) were synthesized from the corresponding thioglycosides, and the influence of the C(alpha)-C(beta)-C(gamma)-H(gamma) torsion angle and substituent effects on the three-bond carbon-proton couplings was studied. The cis coupling constants range from 1 to 2Hz. The trans couplings are generally as small as 2.3-2.6Hz; however, for compounds bearing an unsubstituted gamma-carbon, a relatively large trans coupling was measured (4.8Hz). An S-ethyl group at the beta-position increases the cis coupling (up to 3.2Hz) compared to the corresponding O-glycosides.

Preparation of the pentasaccharide hapten of the GPL of Mycobacterium avium serovar 19 by achieving the glycosylation of a tertiary hydroxyl group.

The chemical synthesis of the glycopeptidolipid-type pentasaccharide hapten of Mycobacterium avium serovar 19 with a trifluoroacetamido spacer at the reducing end is described. The spacer-armed pentasaccharide 31, when conjugated to an immunogenic protein, can be applied to the serodiagnosis of mycobacterial infections. The questionable structure of the penultimate monosaccharide unit was clarified as 6-deoxy-3-C-methyl-2,4-di-O-methyl-L-mannopyranose. The occurrence of the 6-deoxy-3-C-methyl-2,4-di-O-methyl-L-talopyranose could be excluded by the presence of the large H-1'-H-2' coupling constant, which proves the 4C1 (L) conformation as the favoured one.

Circular dichroism of 1,3-dioxane-type (2'-naphthyl)methylene acetals of glycosides.

The CD spectra are reported for a series of 1,3-dioxane-type 4,6-O-(2'-naphthyl)methylene acetals of carbohydrates with and without interacting aromatic protective groups on the C-1, C-2, and C-3 hydroxy groups. In the absence of interacting chromophores, the signs of the (1)B transitions are not sensitive to the configuration of C-4, while the signs of the weak (1)L(a) bands are opposite in the galacto and gluco derivatives. The equatorial parallel conformation is found to be the preferred conformation of the 2-naphthyl group in the solid state by X-ray diffraction. The intense (1)B(a) and (1)B(b) transitions of the naphthalene chromophore allowed a safe configurational assignment by exciton coupled interaction with the aromatic protective groups in para-methoxyphenyl-beta-D-glycosides. The origin of the observed CEs were deduced and the additivity of the interactions was studied. The direction of the hydrogenolytic cleavage of 4,6-O-(2'-naphthyl)methylene acetal of carbohydrates could also be detected by the (1)B(b) transition of the 2-naphthyl chromophore.

Introducing transglycosylation activity into human salivary alpha-amylase (HSA).

Synthesis of 4-nitrophenyl 1-thio-beta-D-maltoside, maltotrioside, and maltotetraoside in yields up to 60% has been achieved by a Tyr151Met (Y151M) mutant of human salivary alpha-amylase. Y151M is capable of transferring maltose and maltotriose residues from a maltotetraose donor onto different p-nitrophenyl glycosides. (1)H and (13)C NMR studies revealed that the mutated enzyme preserved the stereo- and regioselectivity. The glycosylation took place at position 4 of the glycosyl acceptor, forming the alpha(1-4)glycosidic bond, exclusively. [reaction: see text]

A general method for the synthesis of sugar 2-C-sulfonic acids by 1 --> 2 arylthio group migration in acid-sensitive thioglycosides. Direct transformation of thiotrityl ethers into C-sulfonic acids.

[reaction: see text] Fully protected triphenylmethyl 2-O-mesyl-1-thio-beta-d-gluco- (14) and -alpha-d-mannopyranoside (28) were transformed by a stereoselective intramolecular 1 --> 2 trans-arylthio migration into methyl 2-S-triphenylmethyl-alpha-d-manno- (15) and -beta-d-glucopyranoside (29), respectively, using NaOCH(3) as nucleophile. The 2-S-triphenylmethyl ethers (15 and 29) were directly oxidized to sugar 2-C-sulfonic acids by using oxone (2KHSO(5), KHSO(4), K(2)SO(4)). Compounds (21, 23, 32, and 35) are the first representatives of secondary sugar C-sulfonic acids.

Stereoselective (2-naphthyl)methylation of sugar hydroxyls by the hydrogenolysis of diastereoisomeric dioxolane-type (2-naphthyl)methylene acetals.

The cis axial/equatorial OH groups of methyl alpha-L- and ethyl 1-thio-alpha-L-rhamnopyranoside, 1,6-anhydro-beta-D-mannopyranose, and 1,6-anhydro-beta-D-galactopyranose were reacted with 2-naphthaldehyde dimethyl acetal to diastereomeric dioxolane-type 2,3-O-(2-naphthyl)methylene or 3,4-O-(2-naphthyl)methylene acetals. The glycosides yielded the exo- and endo-isomers in nearly 1:1 ratio, 1,6-anhydro-beta-D-mannopyranose gave predominantly the endo-, and 1,6-anhydro-beta-D-galactopyranose exclusively endo-isomer. The acetals and some of their fully protected derivatives bearing benzyl or tert-butyldimethylsilyl groups were hydrogenolised with AlH(3) (3LiAlH(4)-AlCl(3)) or with Me(3)N.BH(3)-AlCl(3) reagents. The endo-isomers were cleaved by both reagents to give axial NAP ethers, the exo-isomers of pyranosides furnished equatorial NAP ethers. However, the exo-isomers of pyranoses gave irregular axial ethers with a > 30-fold enhancement of the reaction rates with respect to the endo-isomer.

Action pattern and subsite mapping of Bacillus licheniformis alpha-amylase (BLA) with modified maltooligosaccharide substrates.

This study represents the first characterisation of the substrate-binding site of Bacillus licheniformis alpha-amylase (BLA). It describes the first subsite map, namely, number of subsites, apparent subsite energies and the dual product specificity of BLA. The product pattern and cleavage frequencies were determined by high-performance liquid chromatography, utilising a homologous series of chromophore-substituted maltooligosaccharides of degree of polymerisation 4-10 as model substrates. The binding region of BLA is composed of five glycone, three aglycone-binding sites and a 'barrier' subsite. Comparison of the binding energies of subsites, which were calculated with a computer program, shows that BLA has similarity to the closely related Bacillus amyloliquefaciens alpha-amylase.

Mixed acetals of cyclodextrins. Preparation of hexakis-, heptakis- and octakis[2,6-di-O-(methoxydimethyl)methyl]-alpha-, beta- and gamma-cyclodextrins.

The proton-catalyzed addition of 2-methoxypropene to alpha-, beta- and gamma-cyclodextrins resulted in hexakis-, heptakis-, and octakis[2,6-di-O-(methoxydimethyl)methyl]-alpha-, beta- and gamma-cyclodextrins, but no reaction was observed of CD-s with 2,2-dimethoxypropane. The mixed acetal-type compounds can be alkylated under basic conditions. The preparation of hexakis(3-O-benzyl)-alpha-cyclodextrin demonstrates the synthetic value of this methodology.