The 10-thia analog of mesobilirubin-XIIIα, with the central C(10) CH2 group replaced by sulfur (1a) was synthesized by condensation of neoxanthobilirubic acid (3) with sulfur dichloride. Thia-rubin 1a is a brilliant yellow solid, forming bright yellow solutions with uv-visible absorption maximum from 425–440 nm.
amphiphilicity relative to the parent mesobilirubins without the gem-dimethyls and have highly favorable solubility in organic solvents ranging from nonpolar (benzene) to polar (CH3OH). Like the parent rubins, 1a–1d can easily bend about the middle but unlike the parents they cannot form mesobiliverdin analogs. NMR spectroscopic analysis and molecular dynamics calculations indicate that, like the parents