Hexopyranose table

Table X. (1 - 1)-Linked Hexopyranoses Containing One Amino Group. 210...

Prom the viewpoint of a synthesis chemist, carbohydrates would appear to be severely overfunctionalized. Thus, in a hexopyranose, one has to contend with five hydroxyl groups distributed over six carbon atoms. Furthermore, four of the hydroxyl groups are chiral. Obviously, to cany out synthetic manipulations on such molecules one has to learn to protect hydroxyl groups (or amino groups in the case of aminodeoxy sugars) to leave free only those destined for reactions. Therefore, a rich repertoire of protecting gronp manipulations for this purpose has evolved [1,2]. Table 1 shows some of the more common ones in current use. 

The analysis of crystallographic results shows the important role played by the anomeric center in the structure of sugars. In Table I51"59 are reported the C-C and C-0 bond-lengths in some hexopyranoses in both anomeric forms, and in some disaccharides. 

For physical data of l,6-anhydro-/i-D-hexopyranoses and some of their derivatives, see Ref. 13, Tables V-XI, pp. 165-176. 

In accordance with published data on O-acetylated hexopyranoses,69 an a effect of O-acetylation at 0-4 or 0-8 on the 13C NMR chemical shift was positive (2.3-3.2 ppm), whereas p effects of a similar magnitude on the neighboring carbons were negative22,24,31,40 (Table V). 

Dianhydro derivatives are crystalline compounds, readily soluble in water and only slightly soluble in ether (see Table VIII). They constitute a complete series having a very rigid, tricyclic skeleton l,6 2,3-dianhydro-/3-D-hexopyranoses exist in the 5H0(d) conformation, and l,6 3,4-dianhydro-/3-D-hexopyranoses in the 1H0(d) conformation with the conformation of the dioxolane ring approximat-... 

The calculated free-energies given in Table XV are relative to an imaginary hexopyranose that has no non-bonded interactions. The work provides a basis for predicting the stabilities of aldohexo-pyranoses in conformations that may apply to certain reaction intermediates, as well as to sugars in solution. 

Compounds of this class, for example, hexopyranose derivatives having the general formula (123) (see Table II), have most frequently been prepared from the corresponding 6-deoxy-6-iodo or 6-bromo-6-deoxy derivatives of suitably protected aldohexoses or aldohexosides by allowing them to react at room temperature with silver fluoride in pyridine. Alternatively, for example, the 5,6-unsaturated derivative of 1,2 3,4-di-O-iso-propylidene-a-D-galaotopyranose was prepared from the 6-deoxy-6-iodo compound by heating at 130° with sodium methoxide in methanol. Properties of some members of this class are given in Table II. 

Table I shows the agreement between the observed and calculated chemical shifts at H-1 and H-5 in a series of hexopyranose acetates.

In an attempt to determine an empirical set of values for partial rotatory contributions of various conformational elements, in systems devoid of conformational ambiguities, correlations have been made of the optical rotations of the eight l,6-anhydro-j3-D-hexopyranoses and their triacetates (see Table I), the l,6-anhydro-monodeoxy-)3-D-hexopyranoses, and the 2,7-anhydro-/3-D-heptulopyranoses and their acetates. The calculated rotations were found to be in excel-... 

TABLE 6.3 Periodate oxidation of linked hexopyranose residues... 

Table 7.1 Thermally induced cationic polymerization of 1,6-anhydro-j5-D-hexopyranose (la-c) using (S-2-butenyl)tetramethylenesulfonium hexafluoroantimonate (2) ...

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