SYNTHESIS AND PROPERTIES OF C(10) ISOPROPYL AND ISOPROPYLIDENE ANALOGS OF BILIRUBIN

Analogs of bilirubin with isopropyl (1) and isopropylidene (2) groups attached to the central C(10) carbon were synthesized and evaluated by a combination of NMR, UV-vis and circular dichroism spectroscopy and molecular dynamics calculations. These methods and H-1{H-1}-homonuclea r Overhauser effect (NOE) experiments in CDCl3 solutions indicate that the rubins' carboxylic acid groups are tethered to the dipyrrinone la ctams and/or pyrroles by intramolecular hydrogen bonds and confirm tha t the pigments adopt a folded, ridge-tile shape in solution. (C) 1998 Elsevier Science Ltd. All rights reserved.