Glucosamine stereochemistry

As far as the stereochemistry concerns, when the cyclization occurs through a Michael reaction, the thermodynamic product is generally obtained, but some exceptions have been observed such as that of A-acetyl glucosamine protected as 4,6-benzylidene, the reaction of which with [(ethoxycarbonyl)methylene]triphenylphosphorane afforded the ot-C-glycosyl compound stereoselectively.28... 

Total fatty acids were liberated by subjecting Salmonella minnesota Re lipopolysaccharide (or free lipid A) to acidic (4 N HC1, 5 h, 100°C) followed by alkaline (1 N NaOH, 1 h, 100°C) hydrolysis. After extraction (chloroform), the free fatty acids were converted into their methyl esters (diazomethane) and analysed by combined gas-liquid chromatography/mass spectrometry. Alternatively, the fatty acids of lipid A are transesterified by treatment of lipopolysaccharide with methanolic HC1 (2 N HC1 in water-free CHaOH, 18 h, 85°C). By these procedures the following fatty acids were identified (in approximate amounts relative to 2 moles glucosamine) dodecanoic (12 0, 1.1 mole), tetradecanoic (14 0, 0.8 mole), hexadecanoic (16 0, 0.9 mole), 2-hydroxytetradecanoic (2-OH-l4 0, 0.1 mole), and 3-hydroxytetradecanoic acid (3-OH-14 0, 4 moles). In total, therefore, approximately 7 moles of fatty acids are present per mole of lipid A backbone. The stereochemistry of the hydroxylated fatty acids was determined by gas-liquid chromatography of their diastereomeric methoxyacyl-L-phenylethylamide derivatives (24). It was found that 2-hydroxyte-tradecanoic acid possesses the-Ts), and the predominating 3-hydroxytetradecanoic acid the (R) configuration. 

The variety and ingenuity of methods which have subsequently been applied in attempts to clarify the stereochemistry of C2 in glucosamine... 

To go further in understanding the structural chemistry of life we need to know about amino sugars. These molecules allow proteins and sugars to combine and produce structures of remarkable variety and beauty. The most common amino sugars are IV-acetyl-glucosamine and N-acetyl-galac-tosamine, which differ only in stereochemistry. 

It was also found that these alkaloids showed strong antitumor effects in experimental animals [2], although severe toxicity was also observed. However, the third alkaloid isolated, named as mitomycin C, showed excellent antitumor activity, and the toxicity of this alkaloid was low [3]. Mitomycin C is thus utilized clinically as an antitumor antibiotic, especially for stomach cancer [4].The chemical structure of mitomycin C, including its absolute stereochemistry, and that of the related alkaloid porfiromycin have been reported [5,6]. It was established that and -labeled L-glucosamine or L-mannosamine were not incorporated into mitomycins, whereas, D-glucosamine was incorporated. Consequently, six carbons and a nitrogen of D-glucosamine were incorporated as Cj, C2, C3, C9, and Cjo and a... 

Thus, a question arose as to whether the absolute structure of the mitomycins that had been reported previously should be reversed. Reinvestigation of the x-ray crystallography of a mitomycin C derivative established that the previous report on the stereochemistry of mitomycins was erroneous [9]. The other unit in the molecule, except for the D-glucosamine-incorporated carbon atoms of the mitomycins, is derived from an m-CyN unit. 

By contrast, better diastereoselectivity was observed in the synthesis of 3-amino-oxaphosphinanes 42a and 42b (Scheme 9). Then mixing alkylamino-arabinofuranoses 41, directly prepared from the reaction of 2,3,5-tri-O-benzyl-D-arabinofuranose 38 with an excess of a primary amine (i.e., benzylamine or aUylamine), gave mainly one diastereomer with a glucosamine-like stereochemistry (42a or 42b). 

Two new streptomycin analogues, ashimycins A and B, have been isolated from the fermentation broth of griseus these are streptomycin derivatives modified in the L-glucosamine unit, ashamycin A (1, part structure) carrying a glycosidically linked branched-chain sugar acid (the stereochemistry has not been established). ... 

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