Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Wiadomości Chemiczne

Powiadomienia systemowe

Sesja wygasła!

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: D-glukozamina

Sortuj według:

Ogranicz wyniki do:

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.

Osłony grupy aminowej w D-glukozaminie

Bednarczyk D., Myszka H.

Wiadomości Chemiczne

2001

[Z] 55, 5-6

491--515

Aminosugars widely exist as a part of biologically important natural products. They are found in some antibiotics, polysaccharides, lipopolysaccharides, glycolipides, glycoproteins and blood group determinants. Most wide-spread aminosugars are 2-amino-2-deoxyaldoses and among them D-glucosamine. Because of its abundance of occurrence and function fulfilled, this aminosugar is often used in the synthesis of glycosides, as well as a glycosyl donor or acceptor. The methods of synthesis of glycosides have been well known for many years. The classical Koenigs-Knorr method is one of the oldest methods for the preparation of glycosides and requires glycosyl halides as donors (most often bromide or chloride) and heavy metal salts (mainly mercury and silver) as a promoter. The alternative procedure is the imidate method, which requires the use of 1-O-trichloroacetimidate derivative of sugar as glycosyl donor and BF3 ź Et2O or trimethylsilyl triflate as promoter. Apart from these two ways, others should be mentioned, namely: the orthoester and thioglycoside method, those methods using of glycals, 1,2-anhydrosugars and pent-4-enyl glycosides. However, these methods have been known for many years ( and still modified ( the selective synthesis of glycosides still determines the main challenge in the chemistry of carbohydrates. The course of reaction, its stereoselectivity, speed and yield depend on many factors, the most important of which seem to be: the leaving group at the anomeric carbon atom in donors, the conditioners of the reaction ( solvent, temperature, promoter and a character of the protecting groups at almost all carbon atoms ( especially at carbon C-2, as this group can constitute part of the so-called participating group in the process of creation of the glycoside bond. Description of the glycosylation mechanism can be found in many papers. Several new amino protecting groups have been described recently, particularly for the (NH2 function in D-glucosamine. Choice of the 2-amino protecting group is very important and will have a strong influence on the synthesis of the desired glycosides. In this paper we would like to describe the most popular protecting groups. They belong to different group-types, among which we can find: (i) amides ( acetyl (NHAc), trifluoroacetyl (NHTFAc), diacetyl (NdiAc), pent-4-enoyl (NHPent); (ii) imines ( p-methoxybenzylidene (NBzlOMe); (iii) carbamates ( allyloxycarbonyl (NHAloc), 2,2,2-trichloroethoxycarbonyl (NHTroc) and other alkoxycarbonyl (NHAlkoc) ; (iv) cyclic imides ( phthaloyl (NPhth), 4-nitrophthaloyl (NNP) , 4,5-dichlorophthaloyl (NDCP), tetrachlorophthaloyl (NTCP), diphenylmaleyl (NDPhM), thiodiglycoloyl (NTDG) and dithiasuccinoyl (NDts), which are exemplified below.