An intramolecularly hydrogen bonded dihydrotripyrrinone

A yellow tripyrrole analog (1) of bilirubin has been synthesized, and its l one propionic acid group is found to engage in conformation determining, in tramolecular hydrogen bonding in solution and in the crystal. Molecular mod elling and X-ray crystallography reveal an abbreviated ridge-tile or L-shap e conformation in which an essentially planar dipyninone is hydrogen bonded to the single opposing propionic acid group. In the (arbitrary) (P)-helici ty ridge-tile, the torsion angles about C(10) are computed to be 55 degrees and 61 degrees by molecular dynamics and found to be 66 degrees and 53 deg rees in the crystal. Such torsion angles lead to an interplanar dihedral an gle (similar to 93 degrees) between the dipyninone and its adjoining pyrrol e that is very close to the dihedral angle (similar to 98 degrees) found in intramolecularly hydrogen bonded bilirubin.