Aza-C-disaccharides: Synthesis of 6-Deoxygalactonojirimycin β-C(1→3) Linked with d-Altrofuranosides and d-Galactose

Synthesis and glycosidase inhibitory activities of 2-(aminoalkyl)pyrrolidine-3,4-diol derivatives

Several 2-(aminomethyl)-and 2-(2-aminoethyl)-pyrrolidine-3,4-diol derivatives have been assayed for their inhibitory activities towards glycosidases. Good inhibitors of alpha-mannosidases must have the (2R,3R,4S) configuration and possess 2-(benzylamino)methyl substituents. Stereomers with the (2S,3R,4S) configuration are also competitive inhibitors of alpha-mannosidases, but less potent as they share the configuration of C(1), C(2), C(3) of beta-D-mannosides rather than that of alpha-D-mannosides. Interestingly, (2S,3R,4S)-2-[2-[(4-phenyl)phenylamino]ethyl]pyrrolidine-3,4-diol (12g) inhibits several enzymes, for instance alpha-L-fucosidase from bovine epididymis (K(i)=6.5microM, competitive), alpha-galactosidase from bovine liver (K(i)=5microM, mixed) and alpha-mannosidase from jack bean (K(i)=102microM, mixed). Diamines such as (2R,3S,4R)-2-[2-(phenylamino) or 2-(benzylamino)ethyl]pyrrolidine-3,4-diol (ent-12a, ent-12b) inhibit beta-glucosidase from almonds (K(i)=13-40microM, competitive).

Stereoselective syntheses of 1,4-dideoxy-1,4-imino-octitols and novel tetrahydroxyindolizidines

A new route for the preparation of four new indolizidines, (1R,2S,6S,7S,8aS)- and (1R,2S,6R,7R,8aS)-1,2,6,7-tetrahydroxyindolizidine (30 and 32) and (1S,2R,7S,8S,8aR)- and (1S,2R,7R,8R,8aR)-1,2,7,8-tetrahydroxyindolizidine (44 and 46), is reported. The synthesis is based on Knoevenagel homologation of the readily available enantiomerically pure pyrrolidin-carbaldehydes 13 and 37followed by asymmetric dihydroxylation of the subsequent alkenyl pyrrolidines and cyclization of the corresponding imino-octitols. The new indolizidines and their precursors (imino-octitols 20, 25, 26) and indolizidinones 28a and 28b have been tested for inhibitory activities toward 26 glycosidases. The enzymatic inhibition of trans-7-hydroxy-d-(-)-swainsonine (44) toward alpha-mannosidases is similar to that described for trans-7-hydroxy-l-(+)-swainsonine (11b) toward naringinase (alpha-l-rhamnosidase from Penicillium decumbens).

Nitrone cycloadditions to isolevoglucosenone: ready access to a new class of directly linked (1-->3)-imino-C-disaccharides

Straightforward access to a new class of d-gulo- and d-allo-derived directly linked (1-->3)-imino-C-disaccharides by means of cycloaddition reactions of enantiopure polyhydroxylated pyrroline N-oxides with isolevoglucosenone is reported. The cycloaddition reactions display a high level of double asymmetric induction, which allows a partial kinetic resolution of a racemic nitrone. [reaction: see text]

New synthesis of pyrrolidine homoazasugars via aminohomologation of furanoses and their use for the stereoselective synthesis of aza-C-disaccharides

The introduction of a formyl group at the anomeric center of 2,3,5-tri-O-benzyl furanoses and substitution of the ring oxygen with a basic nitrogen atom (aminohomologation) was carried out via stereoselective addition of 2-lithiothiazole to N-benzyl, N-furanosylhydroxylamines (masked N-benzyl sugar nitrones), followed by reductive dehydroxylation of the resulting open-chain adducts, and then ring closure via intramolecular displacement of the free hydroxy group by the amino group and unmasking of the formyl group from the thiazole ring. The resulting formyl aza-C-glycosides were transformed into 2,5-dideoxy-2,5-imino-hexitols (pyrrolidine homoazasugars) by reduction of the formyl to the hydroxymethyl group and removal of the O- and N-benzyl groups by hydrogenolysis. This reaction sequence was applied to four furanoses (D-arabino, D-ribo, D-lyxo, L-xylo) to give the hydroxy- and amino-free homoazasugars, including the natural product 2,5-dideoxy-2,5-imino-D-mannitol, in 17% overall yields (six steps). The formyl aza-C-glycosides proved to be valuable intermediates for the synthesis of more complex derivatives. In fact, these sugar aldehydes were employed in Wittig-type coupling reactions with galactose and ribose phosphoranes to give bis-glycosylated alkenes, which upon reduction of the double bond were transformed into methylene isosteres of (1-->6)- and (1-->5)-linked disaccharides in which one of the two sugar moieties was an azasugar (aza-(1-->x)-C-disaccharides).

Synthesis and enzymatic evaluation of five-membered iminocyclitols and a pseudodisaccharide

Described here are the synthesis of five-membered iminocyclitols with galacto-configuration and a pseudodisaccharide, and their inhibitory activities against beta-galactosyltransferase, beta-galactosidase and alpha-mannosidase.

Synthesis and evaluation as glycosidase inhibitors of 2,5-imino-D-glucitol and 1,5-imino-D-mannitol related derivatives

Selectively functionalized 2,5-imino-D-glucitol and 1,5-imino-D-mannitol derivatives were synthesized and tested as precursors of hydrolytically resistant pseudo-disaccharides. Among them N-acetyl-6-amino-6-deoxy-2,5-imino-D-glucitol (11) and N-acetyl-6-amino-6-deoxy-1,5-imino-D-mannitol (12) were found potent and specific inhibitors against beta-D-glucosidase and alpha-L-fucosidase, respectively.

Straightforward Synthesis of (1-->2)-Linked Pseudo Aza-C-disaccharides by the Novel Cycloaddition of Enantiopure Cyclic Nitrones to Glycals

The novel, highly stereoselective, intermolecular cycloaddition reaction of enantiopure cyclic nitrones 8 to 1,2-glycals 9 opens the way to a straightforward synthesis of a broad class of new (1-->2)-linked pseudo aza-C-disaccharides 6, suitable substrates for selective inhibition of glycosidase enzymes. The cycloadditions occur with high stereocontrol, displaying preferential interaction between the bottom face of the glycal and the face of the nitrone anti to the substituent on C-3, with the reagents approaching in an exo fashion. The cycloadditions produced tricyclic isoxazolidines 7 that represent nonreducing pseudo aza-C-disaccharides stable to hydrolytic conditions. The target pseudo aza-disaccharides 6 were obtained by sequential deprotection of the hydroxyl groups and isoxazolidine ring-opening.