Arnold E. Stütz

Iminosugars and Relatives as Antiviral and Potential Anti-infective Agents

Iminosugars have emerged in the literature during mid-1960s as synthetic compounds. Around the same time, the first examples were found in Nature and their interesting enzyme inhibitory properties were recognised. Due to their powerful interference with glycohydrolases (glycosidases) as well as glycosyltransferases, quite a few representatives exhibit notable biological activities. These range from anti-diabetic, insect antifeedant, nematicidal, plant growth regulating to immunomodulating, anti-cancer as well as - in selected cases - anti-infective properties. The latter will be the focus of the following survey.

Einfache Synthesen Von 1,5-Didesoxy-1,5-Imino-D-Glucit (1-Desoxynojirimycin) Und 1,6-Didesoxy-1,6-Imino-D-Glucit Aus D-Glucofuranurono-6,3-Lacton

ABSTRACT 1,5-Dideoxy-1,5-imino-D-glucitol (1-deoxynojirimycin) and 1,6-dideoxy-1,6-imino-D-glucitol were synthesised by simple sequences in seven and six steps, respectively, from D-glucofuranurono-6,3-lactone. Attempts to improve the yield of the crucial regio- and stereospecific introduction of azide into position 5 of suitable derivatives of this substrate are described.

Two isosteric fluorinated derivatives of the powerful glucosidase inhibitors, 1-deoxynojirimycin and 2,5-dideoxy-2,5-imino-d-mannitol: Syntheses and glucosidase-inhibitory activities of 1,2,5-trideoxy-2-fluoro-1,5-imino-d-glucitol and of 1,2,5-trideoxy-1-fluoro-2,5-imino-d-mannitol

Abstract 1,2,5-Trideoxy-2-fluoro-1,5-imino- d -glucitol, the 2-deoxyfluoro derivative of 1-deoxynojirimycin, as well as 1,2,5-trideoxy-1-fluoro-2,5-imino- d -mannitol and 2,5-dideoxy-2,5-imino-1- O -methyl-d-mannitol, two new analogues of the natural product and powerful glucosidase inhibitor 2,5-dideoxy-2,5-imino- d -mannitol, were synthesised featuring glucose isomerase-catalysed aldose-ketose interconversion reactions as the key steps of the syntheses. Results of inhibition studies conducted with these compounds and previously obtained deoxyfluoro derivatives of 1-deoxynojirimycin, employing glucosidases from various sources, showed that the replacement of a hydroxyl function by fluorine caused an impairment of the inhibitory potency. This effect was smallest for the hydroxyl group at C-6 up to four orders of magnitude larger for replacements at C-2 and C-3. Title compounds were synthesized by chemical and chemo-enzymatic routes.

Structural and mechanistic insight into N-glycan processing by endo-α-mannosidase.

N-linked glycans play key roles in protein folding, stability, and function. Biosynthetic modification of N-linked glycans, within the endoplasmic reticulum, features sequential trimming and readornment steps. One unusual enzyme, endo-α-mannosidase, cleaves mannoside linkages internally within an N-linked glycan chain, short circuiting the classical N-glycan biosynthetic pathway. Here, using two bacterial orthologs, we present the first structural and mechanistic dissection of endo-α-mannosidase. Structures solved at resolutions 1.7–2.1 Å reveal a (β/α)8 barrel fold in which the catalytic center is present in a long substrate-binding groove, consistent with cleavage within the N-glycan chain. Enzymatic cleavage of authentic Glc1/3Man9GlcNAc2 yields Glc1/3-Man. Using the bespoke substrate α-Glc-1,3-α-Man fluoride, the enzyme was shown to act with retention of anomeric configuration. Complexes with the established endo-α-mannosidase inhibitor α-Glc-1,3-deoxymannonojirimycin and a newly developed inhibitor, α-Glc-1,3-isofagomine, and with the reducing-end product α-1,2-mannobiose structurally define the -2 to +2 subsites of the enzyme. These structural and mechanistic data provide a foundation upon which to develop new enzyme inhibitors targeting the hijacking of N-glycan synthesis in viral disease and cancer.

Fluorous iminoalditols: a new family of glycosidase inhibitors and pharmacological chaperones.

A collection of new reversible glycosidase inhibitors of the iminoalditol type featuring N‐substituents containing perfluorinated regions has been prepared for evaluation of physicochemical, biochemical and diagnostic properties. The vast variety of feasible oligofluoro moieties allows for modular approaches to customised structures according to the intended applications, which are influenced by the fluorine content as well as the distance of the fluorous moiety from the ring nitrogen. The first examples, in particular in the D‐galacto series, exhibited excellent inhibitory activities. A preliminary screen with two human cell lines showed that, at subinhibitory concentrations, they are powerful pharmacological chaperones enhancing the activities of the catalytically handicapped lysosomal D‐galactosidase mutants associated with GM1 gangliosidosis and Morquio B disease.

Syntheses of sugar-related trihydroxyazepanes from simple carbohydrates and their activities as reversible glycosidase inhibitors.

Five diastereomeric trideoxy-1,6-iminohexitols were synthesised, and their inhibitory activities were determined against selected glycosidases. For comparison, 1,4,5-trideoxy-1,5-imino-D-lyxo-hexitol, the 4-deoxy derivative of 1-deoxymannojirimicin, was prepared by enzymatic isomerisation of 6-azido-3,6-dideoxy-D-ribo-hexose into the corresponding 2-ulose and subsequent hydrogenation accompanied by intramolecular reductive amination.

Imino sugars and glycosyl hydrolases: historical context, current aspects, emerging trends.

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.

DLHex-DGJ, a novel derivative of 1-deoxygalactonojirimycin with pharmacological chaperone activity in human GM1-gangliosidosis fibroblasts

G(M1)-gangliosidosis (GM1) and Morquio B disease (MBD) are rare lysosomal storage disorders caused by mutations in the gene GLB1. Its main gene product, human acid beta-galactosidase (beta-Gal) degrades two functionally important molecules, G(M1)-ganglioside and keratan sulfate in brain and connective tissues, respectively. While GM1 is a severe, phenotypically heterogenous neurodegenerative disorder, MBD is a systemic bone disease without effects on the central nervous system. A MBD-specific mutation, p.W273L, was shown to produce stable beta-Gal precursors, normally transported and processed to mature, intralysosomal beta-Gal. In accordance with the MBD phenotype, elevated residual activity against G(M1)-ganglioside, but strongly reduced affinity towards keratan sulfate was found. Most GM1 alleles, in contrast, were shown to affect precursor stability and intracellular transport. Specific alleles, p.R201C and p.R201H result in misfolded, unstable precursor proteins rapidly degraded by endoplasmic reticulum-associated protein degradation (ERAD). They may therefore be sensitive to stabilization by small molecules which bind at the active site and provide proper conformation. Thus the stabilized protein may escape from ERAD processes, and reach the lysosomes in an active state, as proposed for enzyme enhancement therapy (EET). This paper demonstrates that a novel iminosugar, DLHex-DGJ, has potent effects as competitive inhibitor of human acid beta-galactosidase in vitro, and describes its effects on activity, protein expression, maturation and intracellular transport in vivo in 13 fibroblasts lines with GLB1 mutations. Beside p.R201C and p.R201H, two further alleles, p.C230R and p.G438E, displayed significant sensitivity against DLHex-DGJ, with an increase of catalytic activity, and a normalization of transport and lysosomal processing of beta-Gal precursors.

Imino sugars and glycosyl hydrolases

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.

Novel, lipophilic derivatives of 2,5-dideoxy-2,5-imino-d-mannitol (DMDP) are powerful β-glucosidase inhibitors☆

Novel derivatives of the D-glucosidase inhibitor 2,5-dideoxy-2,5-imino-D-mannitol bearing lipophilic aliphatic or aromatic amides attached to C-1 have been found to inhibit beta-glucosidase from Agrobacterium sp. in the nanomolar range. One of them, a coumarin derivative, ranks amongst the most active compounds in the class of reversible glycosidase inhibitors of the iminoalditol type.