Preparative syntheses of 2,6-dideoxy-alpha-L-lyxo-hexose (2-deoxy-alpha-L-fucose) and its D-ribo epimer (digitoxose)

New metal-free one-pot synthesis of α-2-deoxy-Ulosides by microwave-assisted double Michael Addition of β-enamino ketones

New metal-free one-pot synthesis of α-2-deoxy-ulosides in moderate to good yields by microwave-assisted double Michael addition of various O-nucleophiles to β-enamino ketones in the presence of 12 N HCl. These glycosyl additions occurred with high α-stereoselectivity and were complete in 10-25 min in 51-93% yield. In addition, high α-stereoselectivity was also observed when S-nucleophiles were examined.

Total Synthesis of the Naturally Occurring Glycosylflavone Aciculatin

The new flavone-glycoside aciculatin (1), from Chrysopogon aciculatus, has been shown to have cytotoxic, anti-inflammatory, and antiarthritis activity. Further biological studies have been limited because of the limited availability of 1 from natural sources. Herein the first total synthesis of 1 in an overall yield of 8.3% is described. The synthesis involved the regio- and stereoselective glycosylation-Fries-type O-to-C rearrangement to construct the C-aryl glycosidic linkage, followed by a Baker-Venkataraman rearrangement and cyclodehydration to form the flavone scaffold.

Cell surface fucose ablation as a therapeutic strategy for malignant neoplasms

The sugar alpha-L-fucose is overexpressed in many human malignancies, especially on specific glycoproteins, glycolipids, certain mucins, and putative cell adhesion ligands found on cancer cell surfaces. Many of these molecules are known or suspected mediators of cell-cell adhesion, cell signaling, motility, or invasion. As knowledge of fucose metabolism evolves and specific mechanisms of its distribution and incorporation are more exactly documented, modulation of fucose expression in cancer is becoming increasingly more feasible. The authors propose that cancer cell surface alpha-L-fucose is a logical target for selective therapeutic ablation. Reduction of fucose content on the surfaces of malignant cells should effectively cripple the cells' physiologic functions by altering or dysregulating cell-cell or cell-matrix interactions, critical for maintaining the malignant phenotype. Significant therapeutic benefits might include modulation of adhesion abnormalities in the cancer cells, reduction of cancer cell motility or invasiveness, reexposure to immune surveillance, or a combination of these events.

Modeling of deoxy- and dideoxyaldohexopyranosyl ring puckering with MM3(92)

Extensive variations of the ring structures of three deoxyaldohexopyranoses, L-fucose, D-quinovose, and L-rhamnose, and four dideoxyaldohexopyranoses, D-digitoxose, abequose, paratose, and tyvelose, were studied by energy minimization with the molecular mechanics algorithm MM3(92). Chair conformers, 4C(1) in D-quinovose and the equivalent 1C(4) in L-fucose and L-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the D-dideoxyhexoses, 4C(1) is again dominant, but with increased amounts of 1C(4) forms in the alpha anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both alpha and beta anomers of the 2,6-dideoxyhexose D-digitoxose. In general, modeled proton-proton coupling constants agreed well with experimental values. Computed anomeric ratios strongly favor the beta configuration except for D-digitoxose, which is almost equally divided between alpha and beta configurations, and L-rhamnose, where the beta configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial beta anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.

Synthesis of (S)-2-fluoro-L-daunosamine and (S)-2-fluoro-D-ristosamine

Derivatives of (S)-2-fluoro-L-daunosamine and (S)-2-fluoro-D-ristosamine were synthesized, starting ultimately from 2-amino-2-deoxy-D-glucose which was converted, according to the literature, into methyl 2-benzamido-4, 6-O-benzylidene-2-deoxy-3-O-(methylsulfonyl)-alpha-D-glucopyranoside (2). Treatment of 2 with tetrabutylammonium fluoride gave a 63% yield of (known) methyl 3-benzamido-4,6-O-benzylidene-2,3-dideoxy-2-fluoro-alpha-D-altropyran oside (4), together with a 6% yield of its 2-benzamido-2,3-dideoxy-3-fluoro-alpha-D-gluco isomer. From 4, the corresponding 6-bromo-2,3,6-trideoxyglycoside 4-benzoate (6) was obtained by Hanessian-Hullar reaction. Dehydrobromination of 6, followed by catalytic hydrogenation of the resulting 5-enoside, and subsequent debenzoylation and N-trifluoroacetylation, afforded the fluorodaunosaminide, methyl 2,3,6-trideoxy-2-fluoro-3-trifluoroacetamido-beta-L-galactopyranos ide. Reductive debromination of 6, followed by debenzoylation and N-trifluoroacetylation, gave the fluororistosaminide, methyl 2,3,6-trideoxy-2-fluoro-3-trifluoroacetamido-alpha-D-altropyran oside. The 1H-n.m.r. spectra of the new aminofluoro sugars are discussed with respect to the effects of neighboring amino and acylamido substituents on geminal and vicinal 1H-19F coupling constants, in comparison with the reported effects of oxygen substituents.