Amphiphilic dipyrrinones: methoxylated [6]-semirubins |
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Authors: | Sanjeev K Dey |
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Institution: | Department of Chemistry, University of Nevada, Reno, NV 89557-0216, USA |
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Abstract: | Replacing the typical β-alkyl substituents of 6]-semirubin and 6]-oxosemirubin, two intramolecularly hydrogen-bonded bilirubin analogs, with methoxy groups produces amphiphilic dipyrrinones. Synthesized from the respective 9H-dipyrrinones prepared by base-catalyzed condensation of 3,4-dimethoxypyrrolin-2-one with the appropriate pyrrole α-aldehyde, the 2,3-dimethoxy and 2,3,7,8-tetramethoxy analogs of 6]-semirubin are yellow-colored dipyrrinones that form intramolecularly hydrogen-bonded monomers in CDCl3, as deduced from 1H NMR NH chemical shifts. They are monomeric in CHCl3, as determined by vapor pressure osmometry. In contrast, in the solid, X-ray crystallography reveals supramolecular ribbons of intermolecularly hydrogen-bonded (dipyrrinone to dipyrrinone and acid to acid) 2,3,7,8-tetramethoxy-6]-semirubin. The latter is approximately 20 times more soluble in water than the parent 6]-semirubin with four β-methyl groups. |
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Keywords: | Dipyrroles NMR X-ray crystallography Aqueous solubility |
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