SYNTHESIS OF BILIVERDINS WITH STABLE EXTENDED CONFORMATIONS .2.

The synthesis of two hexacyclic and one heptacyciic biliverdin with ex tended conformations was achieved using base catalyzed intramolecular substitution reactions of 2-chloroethyl biliverdins. The 2-chloroethyl residues were located at selected beta-pyrrole positions as to enable them to react with proximal basic nitrogens at the adjacent pyrrole r ings. Seven membered rings were thus formed which distorted either two or the three exocyclic double bonds at the biliverdin meso-bridges aw ay from their usual Z-syn configuration. The hexacyclic biliverdin 9 i s isomorphous with the chromophores of C-phycocyanin, biliverdin 19 is an isomer of isophorcabilin, and the heptacyclic biliverdin 34 has th e fullest extended conformation that the biliverdin backbone can achie ve.