CONCERNING THE QUESTION OF COVALENT BONDING IN HYPERICIN-CHROMOPROTEINS - SCHIFF-BASE FORMATION

Depending on the reaction conditions, peri-hydroxy substituted anthraquinones like 1,8-dihydroxyanthraquinone and 1,4-dihydroxyanthraquinone could be derivatized with ammonia, propylamine, isopropylamine, and a lysine derivative to yield a variety of imino and amino substitution and addition products. However, hypericin resisted such derivatization under a variety of reaction conditions. Therefore, the hypothesis that hypericin is bound to its apoprotein in photopigments via a Schiff base to the epsilon-amino group of a lysine residue or a terminal amino group seems to be rather unlikely.