A monosaccharide, or simple sugar, which has been modified into an amine by the replacement of a hydroxyl group (one oxygen molecule and a hydrogen molecule) with an amino group (one nitrogen molecule and two hydrogen molecules).
One result of the introduction of the powerful new techniques was the discovery of many new saccharides, both simple and complex. In recent years the number of rare sugars isolated from natural sources has increased rapidly. They have provided the carbohydrate chemist with new and challenging problems of structural determination and synthesis. I shall illustrate this state of affairs with examples from an area in which I have been active, the amino sugars: sugars in which one or more hydroxyls are replaced by an amino group.
In 1875 a young physician named George Ledderhose was working during the summer semester in the laboratory of Friedrich Wohler in Gottingen when Ledderhose's uncle, Felix Hoppe-Seyler, a noted physiological chemist, invited him to dinner. At his uncle's suggestion he took the remains of the lobster they had eaten back to the laboratory, where he found that the claws and the shell dissolved in hot concentrated hydrochloric acid and that on evaporation the solution yielded characteristic crystals. He soon identified the crystalline compound as a new nitrogen-containing sugar, which he named glycosamin.
During the next 20 years much evidence was gathered to indicate that the new sugar has a structure derived by the replacement of the hydroxyl group attached to carbon No. 2 in the glucose molecule by an amino group. With the synthesis, which was still not definitive, of the amino sugar by Emil Fischer and H. Leuchs in 1903 the problem of its structure appeared to have been solved. The structure of glucosamine was unequivocally established, however, only in 1939, when Norman Haworth achieved an unambiguous synthesis that proved Fischer was correct in assigning the "gluco" structure to the amino sugar.
A second amino sugar, galactosamine, was isolated in 1914 by P. A. Levene and Frederick B. La Forge at the Rockefeller Institute for Medical Research from acid hydrolysates of cartilage, tendon and aorta, but its structure was firmly established only in 1945, again attesting to the enormous difficulties such substances present. At the time that was thought to be the end of the amino-sugar story.