Anhydro sugars configurational isomers

Anhydro Sugars as Intermediates in the Interconversion of Configurational Isomers... 

Other epoxy derivatives of pyranose sugars do not show any regularity in the direction of scission. Methyl 2,3-anhydro-4,6-di-0-methyl-/3-n-mannopyranoside reacts with ammonia to afford predominantly the product with the D-altro configuration, but with sodium methoxide equal amounts of T>-altro and D-gluco isomers are obtained.No useful rules could be formulated to predict the direction of opening of epoxides by acidic reagents. ... 

Several 4-deoxy-4-nitro ketose derivatives have been synthesized. Three crystalline 2,7-anhydro-4-deoxy-4-nitro-/3-D-heptulopyranoses arose by nitromethane cyclization92 of the dialdehyde (74) produced by periodate oxidation of sedoheptulosan (73), and were assigned93 the D-alio (75), D-gulo (76), and D-altro (77) configurations by nuclear magnetic resonance spectroscopy of the corresponding, peracetylated amino sugars. When the cyclization of 74 was performed in methan-olic medium, a solid mixture of stereoisomeric nitronates was obtained in almost quantitative yield, and it could be partially separated into the individual nitronates, which furnished 75 and 76. The isomer 77... 

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