Chitonic acid preparation

The best known 2,5-anhydro hexose is that which was prepared in 1894 by Fischer and Tiemann4 and named by them chitose. Chitose is a liquid with ill-defined properties and is usually characterized by its oxidation derivatives, chitonic acid and isosaccharic acid. It is prepared by the deamination of the naturally occurring chitosamine (D-glu-cosamine). 

Various types of commercially available chiral precursors, generally members of the chiral pool, have been used for the stereoselective synthesis of chiral 5,6-dihydropyran-2-ones [6] (i) carbohydrates, mainly monosaccharides 7, 19, 30] (ii) chiral hydroxy acids [8, 20, 31] (iii) chiral epoxides [9, 21, 32] and (iv) other various types of chitons, including those prepared with the aid of microorganisms or enzymes [10, 22, 33]. As discussed above, there are cases in which one or two of the stereogenic carbons of the chiral precursor are transmitted intact to C-5/C-6 of the pyrone ring of the target molecule. In other cases, however, these carbons are not transferred as such and may even disappear, but only after they have influenced the formation of other stereocenters via internal induction. 

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