Cyclitols aqueous solutions

A tandem enzymatic aldol-intramolecular Homer-Wadsworth-Emmons reaction has been used in the synthesis of a cyclitol.310 The key steps are illustrated in Scheme 8.33. The phosphonate aldehyde was condensed with dihydroxyacetone phosphate (DHAP) in water with FDP aldolase to give the aldol adduct, which cyclizes with an intramolecular Horner-Wadsworth-Emmons reaction to give the cyclo-pentene product. The one-pot reaction takes place in aqueous solution at slightly acidic (pH 6.1-6.8) conditions. The aqueous Wittig-type reaction has also been investigated in DNA-templated synthesis.311... 

Remarkable selectivity has been observed in the oxidation of molecules containing several secondary hydroxyl groups, such as al-dopentopyranosides, 6-deoxyaldohexopyranosides, cyclitols, and various anhydro derivatives. As indicated previously, attack usually occurs at relatively hindered hydroxyl groups. When aqueous solutions of benzyl /3-D-arabinopyranoside, benzyl jS-D-ribopyranoside,... 

Of all the polyhydroxy compounds studied in aqueous solution,63 os-inositol exhibits the greatest mobility. The ept- and aUo-inositol and o s-quercitol also Bhow considerable movement, but to a lower degree other cyclitols are Iobs mobile. Reducing sugars and alditols generally show very little or no movement in the presence of Mg29 and alkali metal ions all move in the presence of Ca , Sr , and Ba1 , but the rates are only moderate. Table III gives the relative mobilities of several polyhydroxy compounds in aqueous solutions of various metal ions. 

The reduction of inososes is a method much used for the preparation of new cyclitols. Catalytic hydrogenation in neutral, aqueous solution yields predominantly the isomer with the newly formed hydroxyl group in the axial position,210 whereas the product from a reduction by sodium amalgam usually contains considerable quantities of both the possible epimers.211 Recently, sodium borohydride has been used for reducing inososes62,68 211 in some cases, but not in others, it provides more of the equatorial isomer than does sodium amalgam. 

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