72 GENERAL BIOCHEMISTRY 



Alcohols 



Reduction of the semiacetal group yields the corresponding polyal- 

 cohols. The most important are sorbitol, dulcitol, mannitol, and 

 ribitol, corresponding to glucose, galactose, mannose, and ribose re- 

 spectively. The first three occur in small amounts in plants, and ribitol 

 is one of the components of the vitamin riboflavin. 



A different type of polyalcohol, represented by inositol, is not 

 derived directly from a sugar but is a derivative of cyclohexane. Inosi- 

 tol possesses chemical properties similar to those of sorbitol and the 

 others and is included here for that reason. The structure is as fol- 

 lows: 



OH OH 



A number of isomers are possible, the one shown being 7neso-inosho\. 

 It occurs in the phospholipides of the nervous systems of higher ani- 

 mals and is an essential growth factor for certain molds apparently 

 incapable of synthesizing it. 



Glycosides 



This name is the generic term for the acetal derivatives of monosac- 

 charides. According to this definition, the disaccharides and higher 

 carbohydrates are glycosides. However, since these members of the 

 class have already been considered, only the examples based on other 

 alcohols than the hydroxyl groups of carbohydrates will be mentioned 

 here. 



7his group of compounds is exceedingly varied and widespread, 

 including many compounds that will be mentioned later in various 

 connections. Many of the alcohols involved are polyfimctional. The 

 pink and blue pigments of most blossoms and a few yellow colors are 

 glycosides. These plant pigments are discussed on page 197. Another 

 complex group includes the acetals of steroids. Of these compounds 

 many are either animal hormones or plant products with pronounced 

 pharmacological effects on animals. One class of natural detergents. 



