On the chemistry of pyrrole pigments, XCIII: 1,2-bis-(dipyrrinon-9-ylidene)-ethane ? a novelb-homoverdin chromophore

Chen, Q-Q.; Falk, Heinz

doi:10.1007/bf00811380

Cited by 8 publications

(1 citation statement)

References 17 publications

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“…Yet, little is known of 10-homologated rubins, and the known examples are not necessarily forced to be linear. Six years ago, we published on the first (yellow) 10a-homorubin (Figure ), and a year earlier a few simple examples of a new class of (red) dehydro-10a-homorubins, also called b -homoverdins, were synthesized . Subsequently a didehydro-10a-homorubin or dehydro- b -homoverdin (also red), was prepared 12b…”

Section: Introductionmentioning

confidence: 99%

A New Class of Linear Tetrapyrroles: Acetylenic 10,10a-Didehydro-10a-homobilirubins

Ghosh

Lightner

2003

J. Org. Chem.

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Novel bilirubin analogues with dipyrrinones conjoined to an acetylene rather than a methylene group were synthesized and examined spectroscopically. Despite the increased separation of the dipyrrinones forced by replacing a -CH(2)- by a -C(triple bond)C- unit, molecular dynamics calculations show that, like bilirubin, they may still engage in intramolecular hydrogen bonding to carboxylic acid groups when the propionic acid chains are slightly lengthened, e.g., butanoic acids. Unlike bilirubin, however, which is bent in the middle and has a ridge-tile shape, the acetylene orients the attached dipyrrinones along a linear path, and intramolecular hydrogen bonding preserves a twisted linear molecular shape. The extended planes of the dipyrrinones intersect along the -C(triple bond)C- axis at an angle of 136 degrees for the conformation stabilized by intramolecular hydrogen bonding in the bis-butyric acid rubin (1b). With shorter acid chains (propionic), only one CO(2)H can engage an opposing dipyrrinone in intramolecular hydrogen bonding, and in this energy-minimum conformation of the linear pigment 1a, the intersection of the extended planes of the dipyrrinones has an angle of 171 degrees. Spectroscopic evidence for such linearized and twisted structures was found in the pigments' NMR spectral data and their exciton UV-vis and induced circular dichroism spectra.

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Section: Introductionmentioning

confidence: 99%