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Treatment of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altro-pyranoside (128) (42) with 121 followed by refluxing and processing afforded a chloro derivative as a sirup in 70% yield (46, 49). Reduction of this product with an excess of Raney-nickel in methanol containing acetic anhydride afforded a crystalline product, m.p. 179°C., which is formulated as the d-manno analog 131. The actual product is most likely methyl azido-4,6-0-benzylidene-3-chloro-2,3-dideodxy - a - d - mannopyran-oside (130) resulting from attack of chloride ion at C-3 with inversion of configuration in the intermediate 129. Had the chlorination proceeded... 

D-a/to D-altro D-gluco D-manno o-gulo D-ido D-galacto D-talo... 

Analogous reactions of37 provided two other carba-sugar pentaacetates, of the a-DL-marmo (39 29% yield) and -DL-altro form (40 27%). 

From L-arabinose, carba-sugars of the a-D-gluco and h-altro types were prepared from D-arabinose, carba-a-L-mannopyranose from D-ribose, that of the fi-L-manno modification from D-xylose, those of the -L-gluco and a-D-altro forms and, from D-glucose, those of the P-L-allo a-L-... 

Cyclization of 148 with l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and a subsequent elimination reaction with acetic anhydride and pyridine furnished compound 149. °- Compound 149 was found to be an important key compound for the following synthesis of carba-sugars of the a-L-altro, fi-D-gluco, P-h-allo, and a-D manno modifications. 

Carba-sugars of the a-L-altro and P-D-gluco modifications were prepared from 149 by way of 155. 0-Mesylation of 155 with an excess of mesyl chloride and pyridine resulted in formation of the cyclohexenealdehyde 159, accompanied by y -elimination. Reduction of 159 with sodium borohydride gave the cyclohexenemethanol 160, which is the antipode oP 141. 

Analogously to the reaction 141 — 142 +143, hydroboration-oxidation of 160 and acetylation provided carba-sugar derivatives of the a-L-altro (156) and P-D-gluco (161) modification in the ratio of 1 6, which were convertible into 158 and 93, respectively, in the usual way. ... 

C-Glycosyl derivatives may be prepared by utilizing glycosyl fluorides. Ishido and coworkers reported that the reaction of 2,3,5-tri-O-benzyl-a-(36a) or - -D-ribofuranosyl fluoride (36fi) with isopropenyl trimethylsilyl ether under BF3 catalysis (0.1 -0.05 mol. equiv. for the fluoride, in ether or acetonitrile) gave a mixture of 4,7-anhydro-5,6,8-tri-C)-benzyl-l,3-dideoxy-D-altro- (139, major) and -D-a//o-2-octulose (140) 139 was stated to isomerized to 140 (should be vice versa) under Lewis acid catalysis. Similar... 

All known hexosaminuronic acids have an amino group in the 2-position. Seven 2-amino-2-deoxyhexuronic acids are known, namely, those with the D-gluco, D-manno, d- and L-galacto, L-talo, L-altro, and h-gulo configurations. None of these is very common, and some have been found in one... 

Epimerization at C-5 of hexuronic acids is a reaction that proceeds both on the polymer and on the sugar nucleotide level. In addition to the three pairs of parent acids, namely, the u-glucolL-ido-, D manno/L-gulo-, and D-ga-lacto/L-altro-he uron c acids, the 2-amino-2-deoxy acids belonging to the last two and the 2,3-diamino-2,3-dideoxy acids belonging to the middle pair have been found. 

D-erythro-Pentulose 5-phosphate (XLIV) has been formed by the action of transketolase on hydroxypyruvate (XLII) and D-glycerose 3-phosphate, the hydroxypyruvate being decarboxylated196 to active glycolaldehyde which then reacts with the triose phosphate by an acyloin reaction.28 The active glycolaldehyde is also formed from L-glycero-tetrulose, d-altro-heptulose 7-phosphate, D-fructose 6-phosphate, and D-i/ireo-pentulose 5-phosphate and it reacts with various aldehydes (acceptors) to give ketoses.198, 200 Thus, substitution of L-gfh/cero-tetrulose for hydroxypyruvate in the above experiment also resulted in formation of D-en/i/iro-pentulose... 

Esterification of several methyl 4,6-O-benzylidene-D-hexo-pyranosides with one molar equivalent of benzoyl chloride-triethylamine in an inert solvent was found to occur with good selectivity, mainly affording 2-benzoates from the a-D-gluco, a-D-allo, and a-D-altro compounds, and the 3-benzoate from the j8-D-gluco compound.52... 

Buchanan and co workers71 found that treatment of the 7 3 mixture of the D-altro (68) and D-alio (69) hept-l-ynitol derivatives obtained from 2,3,5-tri-O-benzyl-D-ribofuranose and ethynylmagnesium bromide with 2.2 equivalents of p-toluenesulfonyl chloride at 60° gives the 1-D-ribofuranosylethyne derivatives (70 and 71) in 52 and 13%... 

Unlike the behavior of 81, treatment of 2,3,5-tri-O-benzyl-D-ribofuranosyl bromide91 (110) with mercuric cyanide gave an ano-meric mixture of cyanides (111), which was reduced to an epimeric mixture of amines.92 Separation of this mixture by column chromatography gave the D-alio isomer (112), the D-altro isomer (113), and the glycal derivative (114). Compound 112 was, however, formed in moderate yield (18%), presumably because of a preponderance of the a anomer in the mixture of anomeric cyanides (111). Compound 112 was converted92 into the 1-ureido derivative (92) by treatment... 

At the other extreme of reactivity, 2-bromopyridine had to be transformed into the corresponding iodide to achieve good efficiency for the coupling reaction [14], For example, D-altro-2-(2,4 3,5-di-0-benzylidenepentitol-l-yl)-6-bromopyridine (17) was first converted to the corresponding iodide 18, which was then allowed to react with the Reformatsky reagent to give adduct 19. 

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