Atropisomerism in linear tetrapyrroles

Novel bilirubin and biliverdin congeners with propionic acids replaced by o-carboxyphenyl exhibit diastereomerism due to axial chirality about the carbon–carbon single bond linking the o-carboxyphenyl group to a pyrrole ring. Evidence for atropisomerism was found even in the monopyrrole precursor, e...

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Bibliographic Details
Published in:Tetrahedron 2002-09, Vol.58 (37), p.7411-7421
Main Authors: Boiadjiev, Stefan E, Lightner, David A
Format: Article
Language:English
Subjects:
bilirubin
conformation
hydrogen bonding
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Summary:Novel bilirubin and biliverdin congeners with propionic acids replaced by o-carboxyphenyl exhibit diastereomerism due to axial chirality about the carbon–carbon single bond linking the o-carboxyphenyl group to a pyrrole ring. Evidence for atropisomerism was found even in the monopyrrole precursor, ethyl 3,5-dimethyl-4-( o-carboxyphenyl)pyrrole-2-carboxylate. Like bilirubin, o-carboxyphenyl rubin 1a adopts an intramolecularly hydrogen-bonded ridge-tile conformation in nonpolar solvents. In solutions containing optically active amines or human serum albumin 1a exhibits intense bisignate exciton coupling-type induced circular dichroism for its long wavelength absorption near 400 nm. Bilirubin analog 1a , with o-carboxyphenyl groups replacing propionic acids, was synthesized and found to adopt a ridge-tile conformation stabilized by intramolecular hydrogen bonding between COOH and dipyrrinone groups. Considering atropisomerism about the pyrrole–phenyl bond, 1a and 1b each have three atropisomers: a d, l-pair, with anti COOH groups; and a meso, with syn.
ISSN:0040-4020
1464-5416
DOI:10.1016/S0040-4020(02)00827-X