Vitamin E - Structures and Chemistry

Nomenclature

Vitamin E is the generic term used for all of the compounds in this group. The vitamin can exist as two types of structures: the tocopherol and tocotrienol structures. Both structures are similar except the tocotrienol structure has double bonds on the isoprenoid units. There are many derivatives of these structures due to the different substituents possible on the aromatic ring at positions 5, 6, 7, and 8.

 

Notice that there are three chiral centers, at positions 2', 4', and 8', in the phytyl tail. There is thus the possibility of eight stereoisomers. The most abundant of the naturally-occurring forms is the R,R,R form.

The tocotrienols share the same ring structure, but have an unsaturated tail.

 

Position of methyl groups

on aromatic ring

Tocopherol structure Tocotrienol structure
5,7,8 alpha-Tocopherol alpha-Tocotrienol
5,8 beta-Tocopherol beta-Tocotrienol
7,8 tau-Tocopherol tau-Tocotrienol
8 delta-Tocopherol delta-Tocotrienol

 

 

Chemistry

Tocopherols (Vitamin E) are equipped to perform a unique function. They can interrupt free radical chain reactions by capturing the free radical; this imparts to them their antioxidant properties. The free hydroxyl group on the aromatic ring is responsible for the antioxidant properties. The hydrogen from this group is donated to the free radical, resulting in a relatively stable free radical form of the vitamin.

 

 

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