Synthesis of Fluorinated Chlorophylls‐ a and Their Bio/Physico‐Chemical Properties

Pheophytin(Pheo)‐ a as the free base of chlorophyll(Chl)‐ a , was fluorinated at the 20‐position using N ‐fluorobenzenesulfonimide, followed by insertion of a magnesium cation at the central position to afford 20‐fluoro‐Chl‐ a . On the other hand, 3 2 ,3 2 ‐difluoro‐Chl‐ a was obtained from Pheo‐ d possessing the 3‐formyl group by the Wittig reaction using (triphenylphosphonio)difluoroacetate and the successive magnesium insertion. The synthetic 20‐fluoro‐ and 3 2 ,3 2 ‐difluoro‐Chls‐ a showed similar optical properties and enzymatic hydrolysis of the phytyl ester to original (intact) Chl‐ a . By contrast, their 13 2 ‐stereochemical inversion (epimerization) occurred more rapidly, and the removal of their central magnesium (pheophytinization) was more tolerant than Chl‐ a due to the electronic effect of the fluorine atom(s) through the chlorin π‐system in a molecule. Since a fluorine atom is comparable in the size to a hydrogen atom, these chemically stable fluorinated Chls‐ a are promising as the synthetic alternatives to naturally occurring Chl‐ a , and are useful for the structural and functional investigation in oxygenic phototrophs.