William P Pfeiffer1, Sanjeev K Dey2, Heinz Falk3, David A Lightner4. 1. CIMA Labs, Inc., Eden Prairie, MN 55344 USA. 2. Milliken & Company, P. O. Box 1926, Spartanburg, SC 29304 USA. 3. Institut für Organische Chemie, Abteilung für Organische Chemie, Johannes Kepler-Universität Linz, Altenbergerstr. 69, A-4040 Linz, Austria. 4. Department of Chemistry, University of Nevada, Reno, Nevada, 89557-0216 USA.
Abstract
The syntheses are described for centrally expanded bilirubin analogs: b -homorubins with propionic and butyric acid groups in the positions corresponding to the propionic acids of bilirubin. Their syntheses were accomplished by coupling two equivalents of a reactive monopyrrole (5-(bromomethylene)pyrrolin-2-one) to a dipyrrylethane. The corresponding b -homoverdins and dehydro- b -homoverdins were prepared by dehydrogenating the rubins or their dimethyl esters using DDQ. As supported by NMR measurements and molecular mechanics calculations, the homorubins are found to engage in conformation-determining intramolecular hydrogen bonding between the dipyrrinone and carboxylic acid moieties. Likewise, the homoverdins are believed to favor intramolecularly hydrogen-bonded conformations.
The syntheses are described for centrally expanded n class="Chemical">bilirubin analogs: b -homorubins with propionic and butyric acid groups in the positions corresponding to the propionic acids of bilirubin. Their syntheses were accomplished by coupling two equivalents of a reactive monopyrrole (5-(bromomethylene)pyrrolin-2-one) to a dipyrrylethane. The corresponding b-homoverdins and dehydro- b-homoverdins were prepared by dehydrogenating the rubins or their dimethyl esters using DDQ. As supported by NMR measurements and molecular mechanics calculations, the homorubins are found to engage in conformation-determining intramolecular hydrogenbonding between the dipyrrinone and carboxylic acid moieties. Likewise, the homoverdins are believed to favor intramolecularly hydrogen-bonded conformations.