Organische Fluorverbindungen, VII. Synthese von 10-Fluor- und 14-Fluor-vitamin-A-acetat

Fluorinated retinoids and carotenoids

Methods of preparing fluorinated retinoids with labels located on odd-numbered carbons as well on even-numbered carbons and those containing trifluoromethyl groups are reviewed. The use of such retinoids in studies of protein-bound species is summarized, including the application of (19)F NMR spectroscopy for elucidating the mechanism of cis/trans isomerization, restricted rotation within the protein binding pocket, and identification of specific protein-substrate interactions. The fluorine label was also useful for wavelength attenuation of protein-bound species (including formation of NIR absorbing pigments) and for other unique applications. The more limited studies available on fluorinated carotenoids are also reviewed.

Synthesis of Retinals Fluorinated at Odd-Numbered Side-Chain Positions and of the Corresponding Fluorobacteriorhodopsins

Conventional Horner-Wadsworth-Emmons and Wittig condensations were used to fluorinate the odd-numbered positions of the retinal side chain past C(7). The stereochemically labile cis-fluororetinals were easily converted into the most stable trans-fluororetinals, which were incubated with bacterio-opsin. Contrary to expectations, the fluorinated retinals provided artificial pigments with near normal absorption properties, showing that any electrostatic interactions between the fluorine atoms and protein groups were insufficient to prevent normal binding. The new artificial pigments had smaller opsin shifts than did native bacteriorhodopsin, which is interpreted as due either to greater electrostatic interaction between the protonated imine and its counterion, or to local interactions between the fluorine substituents and nearby polar protein groups.

Relationships between structure and activity of retinoids

Structure-function relationships of 19 retinoids were studied in three in vitro systems in defined, serum-free medium. These systems measure effects on differentiation and growth, as well as toxic effects. The ring, side chain, and polar terminal group of natural retinoids all may be modified synthetically to yield highly active compounds. Several retinoid ethers were found to be significantly less toxic than the corresponding carboxylic acids or alcohols.