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D-Glucosamine Derivatives as Ligands in Highly Enantioselective Palladium-catalyzed Allylic Alkylations

Bauer T., Bartoszewicz A.

Polish Journal of Chemistry

2007

Vol. 81, nr 12

2115-2120

The rigid derivative of D-glucosamine bearing single diphenylphosphino benzoic acid moiety was synthesized and applied as the ligand for the allylic alkylations. Best results were obtained for 1,3-diphenylpropenyl acetate (up to 96% ee).

Saponiny steroidowe

Myszka H., Bednarczyk D.

Wiadomości Chemiczne

2005

[Z] 59, 3-4

275--303

Chemistry and biochemistry of glycoconjugates have been a serious challenge for scientists since many years. Among the huge number of glycoconjugates there is a large group of compounds called saponins, specific glycosides that can be found in many plants. However, they can also be collected from some marine organisms. Nowadays, the main source of saponins is the flora of tropical and temperate zones, such a kind of plants: Costus, Discorea, Paris, Solanum, Trigonella, Trillium and Yucca. Furthermore, the large quantities of saponin can be found in food and beverage plants, including oats, peanuts, soybeans, garlic, onion, spinach, leafs of tea, etc. They are active components of some herbs used in therapeutics, e.g. in Poland the fenugreek seeds are used as a decoction for treatment of skin inflammation, moreover they are the components of antisnoring drops, as well as a part of nutrients for culturists. In Orient countries the number of saponins have long been used as pharmaceutical agents, such as those from ginseng, red clover, licorice, horse chestnut, senega and from many others traditional Chinese herbal medicinal plants. The popularity of the discussed group of glycosides comes from their interesting bioactivity. Biological investigations showed that saponins stop the sedimentation process of lipids on the aorta-wall, they slow down the production of sugars, proteins, lipids and bile acids in the liver. Furthermore, they are good antifungal and antibacterial agents, also show an anti-inflammatory and antiallergic activity. It has been found that the crude extract of some plants, especially in the aerial portion, containing the diosgenin glycosides display anti-neoplastic properties against several strains of human cancer cells. Structurally, the saponins are classified as steroid or triterpenoid glycosides depending upon the nature of the aglycone, which is generally called sapogenin. The steroid saponins have cyclopentaphenantrene backbone in aglycone, for example diosgenin, tigogenin, sarsapogenin. Saponins containing nitrogen in aglycone backbone belong also to this group. Triterpenoid saponins have usually 30-carbon atoms in tetra- or pentacyclic aglycone. The carbohydrate residue (hydrophilic part of glycosides), usually a mono-, di-, tri- or tetrasaccharide, is covalently attached to the sapogenin backbone (hydrophobic element). The sugar moiety, in most saponins, is attached to the 3-OH of a sapogenin via the 1,2-trans-glycosidic bond. The difficulties in isolation of homogeneous saponins from natural sources prompted chemists to the synthesis of these type compounds. Chemical synthesis could provide a real way to the availability of required saponins. The largest and also the most interesting class of saponins is the first group - the steroid saponins, because of their biological activity. To this group belong three class of compounds: cholestanoic, furostanoic and spirostanoic saponins.