Squalene, biological epoxidation

A prominent example of such a reaction is the biological epoxidation of the poly ene squalene... 

The reactivity of epoxides toward nucleophilic ring opening is responsible for one of the biological roles they play Squalene 2 3 epoxide for example is the biological... 

Squalene is an important biological precursor of many triterpenoids, one of which is cholesterol. The first step in the conversion of squalene to lanosterol is epoxidation of the 2,3-douhle bond of squalene. Acid-catalysed ring opening of the epoxide initiates a series of cyclizations, resulting in the formation of protesterol cation. Elimination of a C-9 proton leads to the 1,2-hydride and 1,2-methyl shifts, resulting in the formation of lanosterol, which in turn converted to cholesterol by enzymes in a series of 19 steps. 

The Opening of Squalene-2,3-Epoxide Steroids are tetracyclic compounds that serve a wide variety of biological functions, including hormones (sex hormones), emulsifiers (bile acids), and membrane components (cholesterol). The biosynthesis of steroids is believed to involve an acid-catalyzed opening of squalene-2,3-epoxide (Figure 14-6). Squalene is a member of the class of natural products called terpenes (see Section 25-8). The enzyme squalene epoxidase oxidizes squalene to the epoxide,... 

The next step is simple—the epoxidation of one of the terminal double bonds—but it leads to two of the most remarkable reactions in all of biological chemistry. Squalene is not chiral, but enzymatic epoxidation of one of the enantiotopic alkenes gives a single enantiomer of the epoxide with just one stereogenic centre. 

Squalene 2,3-oxide has been proposed to account for a vast array of polycyclic triterpenes in natureJ The synthesis of 6-amyrin by van Tamelen and his associates mimics the biological cyclization process, featuring the stereoselective generation of five asymmetric centres during a polyolefinic cyclization of the terminal epoxide Preparation of DIE Component ... 

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