C-Disaccharides of Ketoses

Re(CO)5Br-Catalyzed Coupling of Epoxides with CO2 Affording Cyclic Carbonates under Solvent-Free Conditions

In the presence of a catalytic amount of Re(CO)(5)Br, the coupling of epoxides with supercritical CO(2) without an organic solvent at 110 degrees C has afforded cyclic carbonates in good to excellent yields.

Synthesis and evaluation as sialidase inhibitors of xylo-configured cyclohexenephosphonates carrying glycerol side-chain mimics

Based on a strategy previously reported by us, we have synthesized D-xylo configured cyclohexenephosphonates designed to mimic the transition state of the sialidase reaction. The double bond orientation corresponds to the benchmark inhibitor Neu5Ac2en and we could selectively introduce hydroxyalkyl substituents in order to simulate the glycerol side-chain of neuraminic acid. The inhibitory activity of a set of compounds towards bacterial sialidases was tested and interesting differences in activity were found.

Novel zinc (II)-mediated epimerization of 2'-carbonylalkyl-alpha-C-glycopyranosides to their beta-anomers

2'-Aldehydes and 2'-ketones of alpha-C-glycosides, including the gluco-, galacto-, and manno- series, were epimerized exclusively to their beta-anomers in good-to-excellent yields under basic conditions and in the presence of zinc acetate. The beta-stereoselectivity is independent of the neighboring group at 2-O-substitution of sugar substrates. Therefore, this provides a particularly useful method for the preparation of manno-beta-C-glycosides. The epimerization is likely initiated by the formation of Zn-enolate that is stabilized by intramolecular chelation to the pyranose ring-oxygen to form a syn chair-boat structure. Due to the activation generated by the Zn-O coordination, fission of the C1-O bond occurs, leading to opening of the pyranose ring, which is spontaneously followed by a change in conformation. The more stable anti chair-boat transition state is favored, and the subsequent hetero-intramolecular Michael addition results in the formation of beta-C-glycoside in a ring-closure step.

An olefin metathesis route for the preparation of (1-->6)-linked C-disaccharide glycals. A convergent and flexible approach to C-saccharide synthesis

A convergent route to a variety of C-1-disaccharide glycals based on the olefin metathesis reaction of enol ethers and alkenes is described. The DCC-mediated coupling reaction of a variety of pentose enitols (1a-c) with a number of C-5- and C-6-monosaccharide carboxylic acids (2a-e) gave the corresponding esters 3a-l in good yield. Methylenation of these compounds was followed by ring-closing metathesis, mediated by the Schrock molybdenum catalyst 8 in warm toluene, to provide the target C-disaccharide glycals 5a-l. The formed enol ether double bond in 5a was then transformed, via standard manipulations, into a variety of C-disaccharide derivatives 21-25.

Synthesis of alpha-C(1-->3)-mannopyranoside of N-acetylgalactosamine, a new beta-galactosidase inhibitor

Radical C-glycosidation of a 3-methylidene-7-oxabicyclo[2.2.1]heptan-2-one derivative with acetobromomannose gave a alpha-C-mannopyranoside that was converted into alpha-D-ManpCH2(1-->3)-D-GalNAc, a C-disaccharide that inhibits beta-galactosidase from jack bean with IC50 = 9.4 microM and Ki = 7.5 microM (mixed mode of inhibition).