Aldohexoses derivatives

The four D aldopentoses and the eight D aldohexoses derived from them by Kiliani-Fischer synthesis are shown in Figure 25.9 (p. 1052), One of the eight aldohexoses is glucose, but which one ... 

The four o aldopentoses and the eight d aldohexoses derived from them by Kiliani-Fischer chain extension. 

The four D aldopentoses and the eight o aldohexoses derived from them by Kilianl-Flscher chain extension. 

The favored conformations of a number of peracetylated 1-thioal-dopyranose derivatives have been examined by use of 220-MHz n.m.r. spectroscopy. For the D-aldohexose derivatives investigated, the Ci(D) conformation was strongly favored, most probably because of the large steric effect of the acetoxymethyl group with the D-aldopentoses, the possibility that the alternative chair conformation was present in appreciable proportion at equilibrium with the (apparently favored) forms having the 1-SAc group equatorially attached could not be discounted the conformational equilibria were measured in a subsequent study (see p. 91). ... 

Heating the sugar with strong acid yields furfural derivatives. Aldohexoses can eliminate water and formaldehyde under these conditions yielding furfural. This adehyde reacts with amines according to I to yield colored Schiff s bases. Ketohex-oses condense with diphenylamine in acid medium with simultaneous oxidation according to II to yield the condensation product shown. 

Heating the sugars with strong add yields furfural derivatives. Under these conditions aldohexoses can eliminate formaldehyde and water to yield furfural. This aldehyde reacts with amines to yield colored Schiff s bases. 

The c.d. spectra of glycuronic acids have been measured in a number of laboratories. " These sugar derivatives, named after the corresponding aldohexose, have the exocyclic hydroxymethyl group on C-5 replaced by the carboxyl chromophore. The structure of /3-D-mannopyranuronic acid is given as an example in formula 9, and the structures of the parent compounds in Fig. 1. 

Most of l,2 5,6-di-0-isopropylidene acetals of the aldohexoses may be selectively (or partially) hydrolyzed to 1,2-0-isopropylidene derivatives. 

Emil Fischer s initial studies [1] focused on dithioacetal formation from a variety of simple aldopentoses, aldohexoses, and aldoheptoses. The products were obtained by simply treating the sugar with an excess of ethanethiol in concentrated hydrochloric acid at low temperature ( 0°C). Many of these dithioacetals have low water solubility, crystallize spontaneously from the reaction mixtures, and can be isolated by simple filtration and washing with odd water. Fischer s key paper [1] also outlined most of the major reaction modes of the diethyl dithioacetal derivatives, later developed in detail, and thus paved the way for subsequent studies into this important class of sugar derivative. 

The mass spectra of aldohexose diethyl dithioacetal pentaacetates resemble those of the corresponding pentose derivatives, but differ in the position of the U, V, W, and AA series, which are situated 72 mass units higher, due to addition of a CHOAc unit to the molecule. 

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