Carbohydrates furanosides

Dalko, P. et al. Recent Advances in the Conversion of Carbohydrate Furanosides and Pyranosides into Carbocycles. 1999 [88]... 

Dalko, P I, Sinay, P, Recent advances in the conversion of carbohydrate furanosides and pyranosides into carbocycles, Angew. Chem. Int. Ed., 38, 773-777, 1999. 

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

A. P. Rauter, J. A. Figueiredo, I. Ismael, and M. S. Pais, Synthesis of x-methy-lene-y-lactones in furanosidic systems, J. Carbohydr. Chem., 6 (1987) 259-272. 

Another successful family of ligands is the sugar-based furanoside ligands 4, 19-23 (Fig. 5) [21-23,43,50]. The modular construction of these ligands allows to fine tune (a) the different configurations of the carbohydrate backbone and (b) the steric and electronic properties of the diphosphite substituents. They show excellent enantioselectivity on both the S and R enantiomer of the product (up to 93%) and excellent regioselectivity (up to 98.8%) under mild conditions (Table 2). 

Furanoside diphosphinite ligands 10 and 11 (Fig. 11) were applied in the Ir-catalyzed asymmetric hydrogenation of several dehydroaminoacid derivatives [25]. The best enantioselectivities (ee s up to 78%) were obtained in the reduction of methyl W-acetamidoacrylate with ligand 10. These results using the lr/10-11 catalysts precursor show that enantiomeric excesses are strongly dependent on the absolute configuration of the C-3 stereocenter of the carbohydrate backbone. The best enantioselectivity were therefore obtained with ligand 10 with an... 

Z)-awh-4-Hydroxy-l-aIkenyl carbamates 363, when subjected to substrate-directed, vanadyl-catalysed epoxidation , lead to diastereomerically pure epoxides of type 364 (equation 99)247,252,269 qqjggg epoxides are highly reactive in the presence of Lewis or Brpnsted acids to form -hydroxylactol ethers 366 in some cases the intermediate lactol carbamates 365 could be isolated . However, most epoxides 364 survive purification by silica gel chromatography . The asymmetric homoaldol reaction, coupled with directed epoxidation, and solvolysis rapidly leads to high stereochemical complexity. Some examples are collected in equation 99. The furanosides 368 and 370, readily available from (/f)-0-benzyl lactaldehyde via the corresponding enol carbamates 367 and 369, respectively, have been employed in a short synthesis of the key intermediates of the Kinoshita rifamycin S synthesis . 1,5-Dienyl carbamates such as 371, obtained from 2-substituted enals, provide a facile access to branched carbohydrate analogues . 

D. Mootoo, P. Wilson, and V. Jammalamadaka, Application of the Keck radical coupling reaction to the preparation of allylated C-5 furanosides and C-6 pyranosides, J. Carbohydr. Chem. 73 841 (1994). 

A. Chiocconi, C. Marino, E. Otal, and R. M. de Lederkremer, Photoinduced electron transfer and chemical a-deoxygenation of D-galactono-1,4-lactone. Synthesis of 2-deoxy-D-/yxo-hexo-furanosides, Carbohydr. Res., 337 (2002) 2119-2126. 

R. K. Ness and H. G. Fletcher, Synthesis of sucrose and of a-D-glucopyranosyl a-D-fructo-furanoside through the use of 1,3,4.6-tetra-O-benzyl-D-fructofuranose, Carbohydr. Res., 17 (1971) 465-470. 

P. A. McNicholas, M. Batley, and J. W. Redmond, Synthesis of methyl pyranosides and furanosides of 3-deoxy-D-marcrco-oct-2-ulosonic acid (KDO) by acid-catalysed solvolysis of the acetylated derivatives, Carbohydr. Res., 146 (1986) 219-231. 

Fructofuranose is found in probably the most well-known and commercially available of all carbohydrates, sucrose. Various derivatives of sucrose are also known in nature, e.g. fatty acid derivatives [91] and agrocinopines [92]. Fructo-furanosides are also present in various plant and bacteria polysaccharides, most often as fructans, but sometimes as a singular component in repeating units [2, 93]. Syntheses of sucrose or derivatives thereof are not very frequent [41, 94-96], and oligosaccharide synthesis with fructofuranosyl donors are even more scarce. 

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