Hexose derivatives

Several other methods for the introduction of halo atoms at C-6 in hexose derivatives have been known since the late 1920s. One of the earlier methods involved the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-glucopyranoside with phosphorus pentachloride which resulted only in an 8% overall yield of methyl 6-chloro-6-deoxy-a-D-glucoside (57). In contrast, the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-altropyranoside with phosphorus tribromide and bromine afforded a 73% yield of the corresponding 6-bromo-6-deoxy derivative (91). 

Fig. 4.—Mass Fragmentography (m/e 161) of Methylated Hexose Derivatives from the Disialosy] Ganglioside. [Top, before treatment with neuraminidase bottom, after treatment with Vibrio cholerae neuraminidase. The methylated hexose derivatives identified are (A) 2,4,6-tri-O-methylgalactose (B) 2,3,6-tri-O-methylglucose (C) 2,3,4,6-tetra-O-methylgalactose. The peaks eluting before C are unrelated signals that were also detected in a blank experiment employing the neuraminidase treatment. Conditions 3% of QF-1, at 190°. Reproduced, by permission, from Ref. 80.]...

FIGURE 7-9 Some hexose derivatives important in biology. In amino sugars, an —NH2 group replaces one of the —OH groups in the parent hexose. Substitution of —H for —OH produces a deoxy sugar note that the deoxy sugars shown here occur in nature as the l iso-... 

G. Fronza, C. Fuganti, A. Mele, and G. Pedrocchi-Fantoni, On the use of (4S,5S)-2-phenyl-4,5-dimethyl-4-formyl-4,5-dihydrooxazole in the synthesis of N-protected 2,3,4,6-tetradeoxy-4-C-methyl-4-amino-L-hexose derivatives, J. Carbohydr. Chem. 70 197 (1991). 

Because of its roles in the synthesis of glycogen, in isomerization of hexose phosphates, and as a precursor for numerous biosynthetic intermediates, UDP-glucose is regarded as a central hexose derivative in mammalian metabolism. In bacteria and plants, both ADP-glucose (production of storage polysaccharide) and UDP-glucose (sugar interconversions and biosynthesis) play important roles as precursors. 

L-Ascorbic acid has also been synthesized from D-galacturonic acid —a hexose derivative not so readily available as D-glucose. In addition, several methods have been reported for the synthesis of 1 starting with L-xylose (a pentose not readily available) and cyanide, or with L-threose (a tetrose not readily available) and a two-carbon fragment. 

BR0M0-6-DE0XY HEXOSE DERIVATIVES BY RIHG-OPENINS OF BEN ZYLIDENE ACETALS WITH N-BROHOSUCCINIMIDE ... 

S. Hanessian 243 6-BR0M0-6-DE0XY HEXOSE DERIVATIVES BY RING-OPENING OF BENZYLIDENE ACETALS WITH N-BROMOSUCCINIMIDE METHYL 4-0-BENZOYL-6-BROMO-6-DEOXY-a-D-GLUCOPYRANOSIDE... 

N. A. Hughes and N. D. Todhunter, Action of acid on 6-thio-hexose derivatives. Synthesis of 1,6-epithio-hexofuranoses, Carbohydr. Res., 326 (2000) 81-87. 

It is not known whether the cyclization of hexose derivatives takes place with the C4- or the C5-hydroxyl group work on model compounds suggests that both the furanoid and the pyranoid rings are possible. Imino-lactone formation is theoretically possible for any 4- or 5-hydroxy nitrile,... 

Further studies were performed several years later, and the results suggested that in the course of the Mitsunobu reaction of O-mesylated 6-.) -acetyl hexose derivatives, the formation of a thietane ring fused to the furanose or the pyranose ring occurred through an oxirane intermediate <2004CAR1787, 2000CAR237>. This topic has already been discussed in Section 2.08.9.1 and presented in Scheme 12 and Equations (23) and (24). 

The finding that the furanone is produced from an Amadori compound was interesting in that it permitted us to test, for the first time, the effect of pH on the products of the reaction. This is not possible using a hexose- derived Amadori compound, because the end products are not stable. The product of 1,2-enolization (3-deoxyosone intermediate) is HMF, which is stable, but the product derived from 2,3 enolization (1-deoxyosone intermediate), maltol and isomaltol are not stable in aqueous solution and thus cannot be detected and measured accurately. In our experiment (Scheme 6), we prepared 1-deoxy-dibenzylamino (13), and -benzylamino (12) D-fructuronic acids, as well as... 

S)-Proline-catalyzed cross-aldol reaction of aldehydes followed by Mukaiyama aldol reaction sequence was used for the synthesis of prelactone B [27]. The products of the aldol reactions of O-protected a-oxyaldehydes are protected carbohydrates, and were also transformed to highly enantiomerically enriched hexose derivatives, again through a second Mukaiyama aldol reaction (Scheme 2.5) [28]. The products of the aldol reactions of N-protected a-aminoaldehyde donor were easily converted to the corresponding highly enantiomerically enriched /Miydroxy-a-amino acids and their derivatives (Scheme 2.6) [24]. (For experimental details see Chapter 14.1.1). 

The effectiveness of various precursors of these compounds was investigated quantitatively by Ottinger and Hofmann.283 Hexose-derived cyclotene was the common precursor for both 33 and 35, as well as 34 and 36. The formation of each compound is very much determined by the nature of the N-containing precursor. Thus, for example, pyrrolidine (e.g., formed by thermal decarboxylation of proline) plus cyclotene produced 33 and 35 only, whereas 1-pyrroline (derived from proline... 

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