Topics in carbohydrate stereochemistry
In its crystal form, D—glycero--L—allo—heptitol is in the 3G form which has a 1,3—parallel interaction btween an xygen and a carbon atom. In solution, the heptitol and its acetate also assume this conformation. Such an interaction, not previously reported for an alditol, has also been found to occur in several other straight—chain sugar derivatives. Characteristic differences were found between the values of carbohydrates on ion—exchange t.l.c. plates in the calcium and in the lanthanum form. Alditols which have a yj sequence of three hydroxyl groups complex better with La(II]I) ions; methyl glycosides complex better with Ca(II) ions. In the Koch—Stuart method of replacing carbon—bound hydrogen atoms with deuterium over Raney nickel, some hydrogen atoms exchange slower than do others, depending on their environment and steric hindrance. Use has been made of these differences in order to prepare selectively deuterium—labelled sugars.