An Instructive Update of Fischer’s Strategy for Assigning Configurations of Chiral Carbons in Linear Aldohexoses
Dumitru Petru I. Iga *
University of București, Former C. I. Parhon, Bulevardul Regina Elisabeta Nr. 4-12, București 030018, Roumania and University of Oradea, Strada Universității Nr. 1, Oradea 410087, Roumania.
*Author to whom correspondence should be addressed.
Abstract
The double salt with Na+ and Rb+ of (+)-tartaric acid made it more seeable by X rays diffraction. Three successive chain shortening of linear aldohexoses produces either D- or L-glyceraldehyde. Those giving D-glyceraldehyde, produces D-erythrose or D-threose by two successive chain shortening, and in this way the configuration of C-4 relative to C-5 is disclosed. Analysis of products of Malaprade oxidation cleavage of 1,2-5,6-di-O-isopropylidene hexitols indicates the configuration of C-2 relative to C-5. A similar result for C3 and C4 as a whole is obtained by isopropylidenation to 1,2-3,4-5,6-tri-O-isopropylidene hexitols, regioselective removing of terminal isopropylidene residues, oxidation cleavage and reducing; C3 and C4 are recovered as isomers of 2,3-O-isopropylidene tetritol, and the configuration of C-4 is cleared by two independent paths. Chain shortening followed by ends equalization, and optical activity measuring, is a versatile method for discerning between symmetrical, irrechi (configurational) and constitutional monosaccharides. Correlation of the results of the above essays unequivocally discloses the structure of all lineary isomeric hexitols and aldohexoses.
Keywords: Linear aldohexoses, configuration, isopropylidenation, chain shortening, malaprade reaction, ends equalization