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1 Wiadomości Chemiczne

1 2001

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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.