Idopyranose 1,6-anhydro

When heated to 100 CC/ D-idose undergoes a reversible loss of water and exists primarily as 1,6-anhydro-n-idopyranose. 

Dermatan sulfate, also termed chondroitin sulfate B, a related glycosaminoglycan constituent of connective tissue, was known to be composed of galactosamine and a uronic acid, originally believed to be glucuronic acid but then claimed to be iduronic acid based largely on color reactions and paper chromatography. However, the d or L-enantiomer status of the latter monosaccharide was not clear. Jeanloz and Stoffyn unequivocally characterized the monosaccharide as L-iduronic acid by consecutive desulfation, reduction, and hydrolysis of the polysaccharide, followed by isolation of the crystalline 2,3,4-tri-0-acetyl-l,6-anhydro-/ -L-idopyranose, which was shown to be identical to an authentic specimen synthesized from 1,2-0-isopropylidene-/ -L-idofuranose.34... 

Notiz iiber l,6-Anhydro-2-S-benzyl-2-thio-/3-l>idopyranose, by L. Vegh and E. Hardegger, Helv. Chim. Acta, 56 (1973) 1961-1962. 

Entsprechende Gleichgewichte stellen sich immer ein, wenn Glyko-side, Oligo- und Polysaccharide einer sauren Hydrolyse unterworfen werden, und auch bei der Einwirkung von wafirigen Sauren auf Aldo-hexosen (sog. Reversion i87,i92,243,253)) Nach der sauren Hydrolyse und Reduktion des P-Heparins wurde aus der dort anwesenden L-Iduron-saure 1,6-Anhydro-p-L-idopyranose (als 2,3,4-Tri-O-acetat) erhalten h... 

All stereocenters in 1,6-anhydrohexopyranoses are of inverted orientation compared to those in the parent 4Ci(d) or 1C4(l) conformations of the corresponding hexopyranoses for example, see 21, 23, and l,6-anhydro-/J-D-glucopyranose (22). In chemical properties, these compounds resemble to a certain degree the methyl /f-D-hexopyranosides. They are relatively stable in alkaline media, but are readily hydrolyzed by acids. In aqueous acid solution, an equilibrium is established between the 1,6-anhydrohexo-pyranose and the corresponding aldohexose, whose composition correlates with expectations from conformational analysis and calculations from thermodynamic data.121 Extreme values, 0.2 and 86%, are observed respectively with 1,6-anhydro-/f-D-glucopyranose (22) and l,6-anhydro-/f-D-idopyranose (the latter has all hydroxyl groups in equatorial disposition). 

Fig. 2-18. Examples of anhydro sugars. 1,1,6-Anhydro-/3-D-glucopyranose (levoglucosan) 2, 1,6-anhydro-/3-D-idopyranose. In 1,6-anhydro derivatives the groups at C-1 and C-5 are both axial.

Anhydro-D-idopyranose is formed from the P anomer because the axial hydroxyl groups on carbons 1 and 6 are close enough for the five-membered ring to form. 

Anhydro- -D-idopyranose (45) Ether Toluene NMI 120 Benzyl bromide 20 50 20 68... 

Another route to 5-amino-5-deoxy-L-idose proceeds from 5-(benzyl-amino)-5-deoxy-l,2-0-isopropylidene-R-L-idurononitrile (56), which is readily obtainable from 1,2-O-isopropylidene-a-D-xj/lo-pentodialdo-1,4-furanose (13) by reaction with benzylamine and hydrogen cy-anide. Partial hydrogenation of the nitrile 56 by the Kuhn procedure, in acid solution, leads to the hexodialdose (57), which is reduced with sodium borohydride to 5-amino-5-deoxy-l,2-0-isopro-pylidene-jS-L-idofuranose. From this compound, tbe acyclic bisulfite adduct (58) is obtained by reaction with sulfiirous acid. Treatment of 58 with barium hydroxide gives crystalline 5-amino-l,6-anhydro-5-deoxy-jS-L-idopyranose (60) in almost quantitative yield. The equilibrium between the pyranose form (61) and its 1,6-anhydride (60) lies far on the side of Ae bicyclic form (60). The equilibrium can be evaluated from the optical rotation of the solution obtained by treat-... 

No formation of 1,6-anhydride is observable in the acid-catalyzed equilibrium mixture from 5,6-bis(acetamido)-5,6-dideoxy-L-idofura-nose. The compound exists only in the furanose form, no 5-acet-amidopyranose or its 1,6-anhydride being chromatographically detectable. Apparently, in this case, the nucleophilicity of the acetamido group is too low for a 1,6-anhydride ring-closure, for the stereochemistry corresponds completely to 176a. 5,6-Bis(acetamido-l,6-anhydro-5,6-dideoxy-j8-L-idopyranose is obtainable, in another way, by acetylation of 5,6-diamino-l,6-anhydro-5,6-dideoxy-/3-L-idopyranose (65) (see Section 11,2 p. 137). It is not a true equilibrium partner of 5,6-bis(acetamido)-5,6-dideoxy-L-idofuranose. 

This difference in the AG values is especially observable in the temperature-dependent, nuclear magnetic resonance spectrum of 5,6-bis(acetamido)-l,6-anhydro-5,6-dideoxy-j8-L-idopyranose. This sugar contains a flve-membered and a six-membered ring amide in... 

Fig. 6.—Nuclear Magnetic Resonance Signals for the Anomeric Protons of 5,6-Bis(acetamido)-l,6-anhydro-5,6-dideoxy-/8-L-idopyranose at Various Temperatures.

In 2,3,4-tri-0-acetyl-l,6-anhydro-)8-D-idopyranose, the most intensive ions are formed by cleavage of the ring between C-1 and C-2 (primary degradation C). In the spectrum of 6-acetamido-2,3,4-tri-0-acetyl-I,6-anhydro-6-deoxy-/3-L-idopyranose, the bicyclic fragments of mass number 168 and 126 are the most intensive ions. They are formed without cleavage of the ring, according to Scheme 2 (primary... 

Since the formation of the anhydrides in acid solution involves an equilibrium, it is more correct to examine the conformations of the end-products of the reaction. An explanation is then apparent. In 1,6-anhydro-/3-D-idopyranose (LXIX), the three free hydroxyl groups are all equatorial in the chair ring known to be present in these anhydrides, and two equatorial hydroxyl groups are present in 1,6-anhydro-(3-o-altropyranose (LXX) and in 1,6-anhydro-/3-D-gulopyranose (LXXI). The known stable types of... 

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