Bilirubin mono and bis-dimethylamides. synthesis,spectroscopy and solution structures

Bilirubin-IXα bis-dimethylamide and 8- and 12-monodimethylamides, and bilirubin-IIIα and XIIIα bis-dimethylamides have been synthesized and characterized spectroscopically. In deuteriochloroform, as deduced from ¹H-nmr N-$\text{H}$ resonances, the mono-dimethylamides prefer a folded, intramolecularly H-bonded conformation characteristic of the parent bilirubins. The possiblity of similar conformations for the bis-dimethylamides is discussed.