ABSTRACT
Steroids are a large group of organic compounds with the perhydro-1, 2-cyclopentano – phenanthrene nucleus, which consists of four fused rings (Fig. 26.1).
Sterols are hydroxylated steroids – that is, they are alcohols derived from steroids. The hydroxyl (OH) group of sterols is usually substituted at position C3. Unsaturation is usually at C5 and often as C7 and C22. The term sterol comes from the Greek (Steros = solid) because the earliest members studied were solid alcohols resulting from the unsaponifiable (i.e. could not be broken down by NaOH) fractions of fats of plants and animals. As the variety of known structures increased the general term steroid came into use about 1935. In higher animals the principal sterol is cholesterol but a wider variety exists in lower animals and in plants (Fig. 26.1).
