Hexopyranoses properties

Physiol Properties of Amino Carba-hexopyranose Penta-A/, O- Acetates... 

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). 

Pratt, J W, Richtmyer, N K, Crystalline 3-deoxy-a-D-nho-hexose. Preparation and properties of 1,6-anhydro-3-deoxy-a-D-arafa>io-hexopyranose, 1,6-anhydro-3-deoxy-p-D-n ho-hexopyranose and related compounds, J. Am. Chem. Soc., 79, 2597-2600, 1957. 

A characteristic feature of these compounds is their steric rigidity in the crystalline state,4 as well as in solution,5 the l,6-anhydro-/3-D-hexopyranoses adopt exclusively the 4C4(d) conformation (la), whereas the corresponding D-hexoses and their glycosides generally occur in the 4Ci(d) conformation. These different conformations determine the chemical and physical properties of the l,6-anhydro-/3-D-hexopyra-noses. A similar situation exists with the 1,6-anhydroaldohexofuranoses. 

During the past ten years, the l,6-anhydro-/3-D-hexopyranoses have found wide application in the synthesis of hexoses and their derivatives, and of oligosaccharides, and for polymerization to polysaccharides. They can be used as model compounds in studying the physical and chemical properties of monosaccharides, as has been shown, for example, by nuclear magnetic resonance (n.m.r.) studies, and also by studies of (a) their chiroptical properties, (b) the partial reactivity of hydroxyl groups, and (c) their ability to form complexes. 

As to the chiroptical properties of 1,6-anhydrohexopyranoses, their [M]d values can be calculated by summation of the molar, optical rotation values for the fundamental skeleton, that is, l,6-anhydro-2,3,4-trideoxy-j8-D-gZycero-hexopyranose (26), and, either the values of the partial, molar contributions of the hydroxyl groups372,373 (see Scheme 3)... 

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. 

Our interest in GOase came from a need to find an efficient process for making 5-C-hydroxymethyl-L-arabino-hexopyranose derivatives 1 (Equation 1). These compounds have been developed as candidates for nonnutritive sugar substitutes in foods because they resist metabolism and have sucrose-like functional properties (7). These materials would be too expensive if made using the techniques of traditional chemical synthesis, so we developed a simple "one-pot" process (Equation 1) using GOase. 

The liquid crystalline properties of dialkylacetals 1 have been described. In the presence of DDQ as catalyst, hexopyranose derivatives having fiee hydroxyl groups at C-6 or at C-S and C-6 reacted with 2,2-dimethojQ propane and acetone to give primary acyclic isopropylidene mixed acetals (e.g., 2 - 3). Non-symmetrical alaketals 5 have been prepared by use of monochloro-dialkyl 4-pentenyl rilyl ethers 4 as reagents, as shown in Scheme 1. ... 

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