Question 21.4: dentifying Sugars and Sugar Derivatives in Polysaccharides F......
Identifying Sugars and Sugar Derivatives in Polysaccharides
Framycetin, a topical antibiotic, is a four-ring molecule consisting of several aminoglycosides—sugars that have some of the —OH groups on the sugars replaced by —NH_2 groups—and another ring, with oxygen links between the rings. What sugar or other molecule is each ring derived from?
ANALYSIS Look at each ring carefully. Ring 2 does not include an O. It cannot be a sugar. Rings 1, 3, and 4 all contain O as a ring member. Imagine the rings as underivatized sugars, that is with —OH groups instead of —NH_2 groups; count the number of carbon atoms in each sugar and draw the sugar form to help identify the sugar.
Ring 2 has six carbon atoms and no oxygen atoms as part of the ring; it is not a sugar, but is a cyclohexane derivative. Rings 1 and 4 are derived from the aldohexose, glucose, while ring 3 is derived from the aldopentose, ribose.