Study of Biological Activity of Vitamin E Using Fluorine as Probe.

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We had synthesized a-tocopherols having one trifluoromethyl group, and studied their behavior and orientation in liposomes using relaxation time on fluorine-NMR.In this case, the results of two experiments for the two trifluoromethyl groups, one on the side-chain and the other on the aromatic ring of a-tocopherol, were compared. Therefore, it was inevitable to eliminate the errors originated in formation of liposomes and measurement of NMR.We thought that most of these experimental errors would be avoided, if one tocopherols with two trifluoromethyl groups were used.In this study, we planned the synthesis of a-tocopherols having two trifluoromethyl groups, one on the side-chain and the other on the chromanol part, and have succeeded in the syntheses of nine possible isomers.Studies of behavior and orientation of vitamin E using these tocopherols showed that a trifluoromethyl group on the chromanol ring is less movable than one on the side-chain. This shows that the chromanol part of vitamin E is oriented to the surface of the membrane and fixed there by the hydrogen bond between the hydroxyl group of the chromanol and hydrophilic part of the membrane near surface, while the side chain is lriented to an inner part of the membrane. Intermolecular force is only van der Waals attraction, so the trifluoromethyl group on the side-chain is more movable.Further, we have synthesized fatty acids fluorinated near to or far from the carboxyl group. When these carboxylic acid were incorporated to liposome, the fluorine near the carboxyl group were much less movable than one far from the carboxyl group. Interestingly, when a-tocopherol was added to these liposomes, the movability of the former fluorine was lessened. This means that vitamin E increases the mechanical stability of the membrane. In other words, vitamin E stabilizes biological membranes not only as an anti-oxidant, but as a mechanical stabilizer.