Cycloalkenes: Sources and Importance
Alkyl-substituted cycloalkenes are frequently found in nature including two important classes of natural products,and steroids. Both share similar biosyntheses and in most cases cyclic structures.
Steroids are widespread in the animal and plant kingdom. Most of the steroids possess a basic structure consisting of four rings and 21-30 carbon atoms. This class includes the important groups of sex hormones, adrenocortical hormones, bile acids, and toad venoms.
Though cholesterol is the most widely distributed steroid, its function in the human body has not been fully determined as yet. An abnormally high cholesterol value in blood leads to atheroma, an accumulation of debris, including cholesterol, at artery walls which can cause cardiovascular disease. Additionally, cholesterol is the main ingredient in gallstones.
Progesterone, the female sex hormone, is formed in the ovaries. It is sometimes called the "hormone of pregnancy" because it prepares the uterus for accepting the fertilized egg and prevents another fertilization during pregnancy. In case of a threatening miscarriage, progesterone is used medically to stabilize the pregnancy. .
Terpenes are natural products which are constructed from isoprene (isoprene=2-methyl-1,3-butadiene) units leading to mostly cyclic or even polycyclic structures. They represent the primary constituents of the essential oils of plants from which they can be generated by steam distillation. They are used widely as fragrancies in perfumery and as spices. Additionally, they are employed as starting materials in the syntheses of vitamins.