Novel Hetero-analogs of Methyl Maltoside Containing Sulfur and Selenium as Potential Glycosidase Inhibitors

Automated Solution-Phase Synthesis of S-Glycosides for the Production of Oligomannopyranoside Derivatives

Thioglycosides are more resistant to enzymatic hydrolysis than their O-linked counterparts, thereby becoming attractive targets for carbohydrate-based therapeutic development. We report the first development of methods for the site-selective incorporation of S-linkages into automated solution-phase oligosaccharide protocols. The protocols were shown to be compatible with the formation of S- or O-glycosides for the synthesis of mannopyranoside trimmers that incorporate both S- and O-linkages to allow the selective incorporation of an S-glycoside in various stages in an automated program.

Bioisosteres of Carbohydrate Functional Groups in Glycomimetic Design

The aberrant presentation of carbohydrates has been linked to a number of diseases, such as cancer metastasis and immune dysregulation. These altered glycan structures represent a target for novel therapies by modulating their associated interactions with neighboring cells and molecules. Although these interactions are highly specific, native carbohydrates are characterized by very low affinities and inherently poor pharmacokinetic properties. Glycomimetic compounds, which mimic the structure and function of native glycans, have been successful in producing molecules with improved pharmacokinetic (PK) and pharmacodynamic (PD) features. Several strategies have been developed for glycomimetic design such as ligand pre-organization or reducing polar surface area. A related approach to developing glycomimetics relies on the bioisosteric replacement of carbohydrate functional groups. These changes can offer improvements to both binding affinity (e.g., reduced desolvation costs, enhanced metal chelation) and pharmacokinetic parameters (e.g., improved oral bioavailability). Several examples of bioisosteric modifications to carbohydrates have been reported; this review aims to consolidate them and presents different possibilities for enhancing core interactions in glycomimetics.

Synthesis of 28a-homoselenolupanes and 28a-homoselenolupane saponins

A practical synthesis of 28a-homo-28a-selenolupane triterpenes and the corresponding selenosaponins containing d-mannose, l-arabinose, l-rhamnose, and d-idose moieties is described. Selenium containing triterpenes were obtained from the readily available 3-O-allyl-homobetulin mesylate by nucleophilic substitution with the selenocyanate ion which upon reduction of the -SeCN group afforded the free selenol. Glycosylation using classical Schmidt donors gave 1,2-trans selenosaponins as the main product as well as minute amounts of 1,2-cis isomers. This is one of the very few examples of the synthesis of selenoglycosides by direct glycosylation of free selenols. The studied selenol showed high resistance to air oxidation resulting in good stability during the synthesis of selenolupane derivatives. Cytotoxic activities of new homoselenolupane derivatives were also evaluated in vitro and revealed that some triterpenes exhibited an interesting profile against human cancer cell lines.

Synthesis and Evaluation of 5-Thio-L-Fucose-Containing Oligosaccharide

5-Thio-L-fucose-containing trisaccharide H-type II was synthesized. The 3',4'-O-isopropylidene-2-azido-2-deoxylactoside derivative, which was prepared from lactose by azidonitration of lactal, was used as a starting material. By regio- and stereoselective 5-thio-L-fucosylation of the 6,6'-dibenzoate 5 with 5-thiofucosyl trichloroacetimidate 6 and subsequent deprotection gave the 5-thio-L-fucose-containing H-type II 1. Conformational analysis of the 5-thio-L-fucose-containing H-type II and the native H-type II was carried out through NOESY experiments. The observed NOE values between N-acetylglucosamine and galactose, and galactose and fucose were same for these two trisaccharides. However, NOE values between fucose and N-acetylglucosamine were significantly different. Binding of the 5-thio-L-fucose-containing H-type II to lectins and antibodies were in some case stronger and in some case weaker than those of the native trisaccharide.

Synthesis of 1,2- and 1,3-N-Linked Disaccharides of 5-Thio-alpha-D-mannopyranose as Potential Inhibitors of the Processing Mannosidase Class I and Mannosidase II Enzymes

The syntheses of S/N acetal heteroatom analogues of 1,2- and 1,3-linked mannopyranose disaccharides are described. The compounds are analogues of the Man-alpha-(1-->2)-Man and Man-alpha-(1-->3)-Man disaccharide components of oligosaccharides found in N-glycoproteins that are cleaved by trimming mannosidases during glycoprotein processing. Glycosylamine formation, without the necessity of hydroxyl group protection, proceeded through acid-catalyzed condensation reactions of 5-thio-D-mannose with either methyl 2-amino-2-deoxy- or 3-amino-3-deoxy-alpha-D-mannopyranoside to give methyl 2-amino-2-deoxy-2-N-(5-thio-alpha/beta-D-mannopyranosyl)-alpha-D-mannopyranoside (2) or methyl 3-amino-3-deoxy-3-N-(5-thio-alpha/beta-D-mannopyranosyl)-alpha-D-mannopyranoside (3), respectively. The superiority of mercuric chloride over acetic acid as a catalyst for this reaction is reported. Acetylation of the anomeric mixtures gave the heptaacetates from which the major beta'-isomers could be separated by chromatography and/or crystallization.

Synthesis of a thio analogue of n-propyl kojibioside, a potential glucosidase inhibitor

The disaccharide alpha-D-Glc p-(1-S-2)-beta-D-Glc p-(1-OPr) 1, a thio analogue of alpha-D-Glc p-(1 --> 2)-alpha-D-Glc p-(1-OPr)(n-propyl kojibioside) in which the inter-glycosidic oxygen atom is replaced by sulfur, has been synthesized for evaluation as a potential glucosidase inhibitor. Glycosylation of the 2-thiol glucopyranosyl acceptor 4 with the trichloroacetimidate of 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranose 5 gave the alpha-linked disaccharide 6 stereoselectively. Deprotection was performed by hydrogenolysis in the presence of Pd/C to give 1 as the beta-n-propyl glycoside. Glycosylation of the thiol 4 with the trichloroacetimidate of 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranose 8 gave a 1:2.3 mixture if the alpha and beta disaccharides (9 and 10); evidence is presented for the occurrence of the orthoester 11, as an intermediate in the formation of the beta-disaccharide.

Thermodynamics of inhibitor binding to the catalytic site of glucoamylase from Aspergillus niger determined by displacement titration calorimetry

The binding of different inhibitors to glucoamylase G2 from Aspergillus niger and its temperature and pH dependencies have been studied by titration calorimetry. The enzyme binds the inhibitors 1-deoxynojirimycin and the pseudo-tetrasaccharide acarbose with association constants of 3 x 10(4) and 9 x 10(11) M-1, respectively, at 27 degrees C. The binding free energy for both ligands is remarkably temperature-invariant in the interval from 9 to 54 degrees C as the result of large compensating changes in enthalpy and entropy. Acarbose and 1-deoxynojirimycin bound with slightly different free energy-pH profiles, with optima at 5.5 and 5.5-7.0, respectively. Variations in delta H degrees and T delta S degrees as a function of pH were substantially larger than variations in delta G degrees in a partly compensatory manner. Two titratable groups at or near subsite 1 of the catalytic site were found to change their pKa slightly upon binding. The hydrogenated forms of acarbose, D-gluco- and L-ido-dihydroacarbose, bind with greatly reduced association constants of 3 x 10(7) and 2 x 10(5) M-1, respectively, and the pseudo-disaccharide methyl acarviosinide, lacking the two glucose units at the reducing end compared to acarbose, has a binding constant of 8 x 10(6) M-1; these values all result from losses in both enthalpy and entropy compared to acarbose. Three thio analogues of the substrate maltose, methyl alpha- and beta-4-thiomaltoside and methyl alpha-4,5'-dithiomaltoside, bind with affinities from 3 x 10(3) to 6 x 10(4) M-1.(ABSTRACT TRUNCATED AT 250 WORDS)