Sorbopyranose conformation

It is most straightforward to begin with a-L-sorbopyranose (1) (see Figure 1) because this sugar shows virtually no mutarotational change in water (I, 7) thus, it remains basically in the a-pyranose form. By analogy with the established (8) structure of the crystalline material, this sugar exists in solution in the 1C(l) pyranose chair conformation (1) because all substituents are thereby optimally oriented—i.e., the... 

Professor Lemieux recalls the following incident from this period. In connection with studies then being performed on solvent effects on conformational equilibria, Dr. Mills suggested that 1,2-O-isopropyli-dene 4-0-methyl-/3-L-sorbopyranose should be examined. The ex-... 

Amino-6-deoxy-L-sorbopyranose (88 = 83) is in equilibrium with the dehydration product (87 = 82). As with the unsaturated compound from 5-amino-5-deoxy-D-xylose (33), this is recognized by its positive Cotton efiFect at 305 nm. The most favored half-chair conformation is shown in 87. In this conformation, C-5 is above the plane of the ring and, according to theory, this situation should lead to a positive Cotton efiFect. 

The n.m.r. spectroscopic investigation of the reactions of pentonolactones with acetone and benzaldehyde in acidic media is covered in Chapter 21, as are conformational studies on 2,3-G-isopropylidene-a-L-sorbopyranose derivatives. l,2-0-Isopropylidene-a-D-t /o-pentodialdo-l,4-furanose dimers are referred to in Ch er 22, and some 7-carbon sugar lactones which were characterized as their isopropylidene-and cyclohexylidene-acetals are noted in Chtytters 2 and 16. 

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