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A procedure is described for the preparation of (S)-dolichol and (S)- nor dolichol starting from the polyprenyl fraction extracted from Gingko biloba integer or exhausted leaves. The procedure appears extremely valuable in obtaining the two chiral isoprenoid compounds in good chemical yields and retention of a high degree of enantiomeric excess. Also, the (S)- nor dolichol represents a good chiral precursor for the preparation of (14)C-labelled (S)-dolichol to be used in biological investigations into the (S)-dolichol catabolism in the functional living cell. Furthermore, the possible role of (S)-dolichol as a free radical scavenger in the cell membrane was preliminarily evaluated by means of a (1)H-NMR analytical method. Apparently, experimental results substantiate this hypothesis.

Dolichol, the polyisoprenoid lipid found in all eukaryotic cells and suggested to represent a biomarker of aging, is inserted into cell membranes, also in tissues exposed to light such as the skin. A general question about its physiological role is whether dolichol may play the role of a natural barrier for the noxious components of solar radiation. In order to clarify this point, we established that dolichol is a component of human sebum and we performed an " in vitro " study of the effects of UV radiation on the spectral properties of dolichol in isopropanol. Our data clearly show that, following UV irradiation, the optical absorption spectrum of dolichol undergoes remarkable modifications below 400 nm: a significant, strongly dose-dependent, increase of the optical density around 320 nm and a minor, very slightly dose-dependent, raise of the absorbance at 250 nm. On the contrary, UV irradiation causes only minor changes in HPLC profiles and the formation of photooxidative products can be considered negligible in our experimental conditions. These results suggest that dolichol can be considered an innate, unusually efficient and promising UV screen for skin protection.