On the conformation of bilirubin dianion

✍ Scribed by Yu-Ming Pu; David A. Lightner

• Publisher: Elsevier Science
• Year: 1991
• Tongue: French
• Weight: 514 KB
• Volume: 47
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)86549-2

✦ Synopsis

&,cr'R)-Mesobilirubin-XIIIa, a tetrapyrrole dicarboxylic acid with P-helicity conformation stabilized by intramolecular hydrogen bonding, exhibits intense bisignate circular dichroism in CHCl, (A&t +246, A,398 -133) and many other solvents, except in (CH,),SO, where the intensity drops lo-fold (EEx + 18, AE~: -9). In contrast, the dicarboxylate anion exhibits intense circular dichroism in both CHC13 (AE~:! + 194, AE$~: -130) and (CH,),SO (Ae;3,3, +260, AE~;; -164). (42,152)-Bilirubin-IXo! (Fig. 1) the cytotoxic yellow-orange tetrapyrrole pigment of jaundice' consists of two dipyrrinone units conjoined by a -CH,-group. Rotation of the dipyrrinones about the central -CH*at C,, generates a large array of conformations,2~3 one of which uniquely places the propionic acid COOH group of one dipyrrinone unit in position for intramolecular hydrogen bonding with the pyrrole and lactam N-H and C=O resides of the other dipyrrinone. Stabilization of this conformation by a network of intra-