A C - H···O=C hydrogen bond? Intramolecular hydrogen bonding in a novel semirubin

M. T. Huggins, D. A. Lightner

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

(4Z)-8-(5-Carboxypentyl)-9-butyl-2,3-diethyl-dipyrrin-1-one (1), a new analogue of xanthobilirubic acid, (4Z)-8-(carboxyethyl)-2,7,9-dimethyl-3-ethyl-dipyrrin-1-one, was synthesized in four steps from the known 2,3-diethyl-dipyrrin-1-one. Whereas xanthobilirubic acid (which is a model for one-half of bilirubin, the yellow pigment of jaundice) and its homologues with hexanoic and longer acid chains at C-8 engage only in intermolecular hydrogen bonding, 1 is found to engage in intramolecular hydrogen bonding. In CDCl3 solution, dipyrrinone 1 adopts an anti-Z conformation, and its hexanoic acid COOH is hydrogen-bonded to the lactam H-N-C=O and to the pyrrole C(7)-H but not to the pyrrole NH. The latter constitutes an example of a hydrogen bond of the type C-H···O=C, weak and detected typically in crystals. Dipyrrinone 1 is found by vapor pressure osmometry to be monomeric in CHCl3, but its methyl ester (2) tends toward being dimeric, like that of methyl xanthobilirubinate, which is dimeric.

Original languageEnglish
Pages (from-to)8402-8410
Number of pages9
JournalJournal of Organic Chemistry
Volume66
Issue number25
DOIs
StatePublished - Dec 14 2001
Externally publishedYes

Scopus Subject Areas

  • Organic Chemistry

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