Crystal and molecular structure of biliverdin dimethyl ester

Abstract

Crystals of the title compound (II) are triclinic, space group P, with a= 12.467(6), b= 14.567(5), c= 9.788(4)Åα= 111.56(3), β= 90.64(4), γ= 97.91(3)°, Z= 2. The biliverdin chromophore, which is in the lactam form with three ‘pyrrole’ N–H protons, takes up a near-planar helical conformation. Two such molecules, related by a crystallographic centre of symmetry are linked into dimers with an extended helical conformation, through two N–H ⋯ O hydrogen bonds (N–H ⋯ O 2.80, N–H 1.12, H ⋯ O 1.74 Å) between symmetry-equivalent pyrrolone rings. A considerable degree of bond fixation is observed within the tetrapyrrole skeleton. The vinyl and one of the methyl ester groups are disordered. The structure was solved by direct methods and refined to R 0.090 for 2 357 diffractometer-measured unique reflections.