STUDIES ON PLANT BILE PIGMENTS–6. PHOTOCHEMICALLY ASSISTED REACTION OF A-DIHYDROBILINDIONE WITH NUCLEOPHILES AS A MODEL FOR PHYTOCHROME INTERCONVERSION

Abstract— –From the A-dihydrobilindione 3. the pyridinium derivatives 6a, b and analogues therwf have been obtained by a formal nucleophilic substitution. The reaction is rationalized as a photochemically assisted oxidation of 3 with a subsequent regioselective addition of pyridine at C-5. By thermolysis. 6a.b yields back the parent bilin 3, together with an oxidation product. The significance of the reaction with respect to the phytochrome interconversion is discussed.