Synthesis and properties of mesobilirubins XIIγ and XIIIγ and their mesobiliverdins
摘要:
The title pigments, with propionic acid groups displaced to the lactam end rings, were synthesized for the first time by the "1 + 2 + 1" approach, coupling two equivalents of a monopyrrole to a dipyrrylmethane (to give XII gamma), or the "2 + 2" approach, self-coupling two equivalents of a dipyrrinone (to give XIII gamma). Using the "1 + 2 + 1" approach, mesobilirubin III alpha was also prepared. Mesobilirubins XII gamma and XIII gamma are more polar than mesobilirubin III alpha and unlike III alpha cannot effectively engage the propionic acid groups in intramolecular hydrogen bonding to the dipyrrinone components. The new mesobilirubins give exciton coupled circular dichroism spectra in the presence of human serum albumin or quinine, with the XII gamma isomer exhibiting Cotton effect intensities nearly as strong as those from the III alpha isomer; whereas, the XIII gamma isomer exhibits far weaker intensities. Mesobilirubin III alpha requires glucuronidation for hepatobiliary elimination; whereas, XII gamma and XIII gamma do not, and they are excreted intact across the liver into bile. The corresponding biliverdins XII gamma and XIII gamma are reduced only slowly by biliverdin IX alpha reductase, in contrast to the fast reduction of the natural IX alpha isomer.
Regioselective Oxidation of Pyrrole Derivatives with DDQ and Its Synthetic Application
作者:Ryoji Iwamoto、Yutaka Ukaji、Katsuhiko Inomata
DOI:10.1246/cl.2010.176
日期:2010.3.5
t-Butyl 4-alkyl-1H-pyrrole-2-carboxylates were oxidized with DDQ in the presence of MeOH at the α-position of the alkyl substituent at the C-4 position regioselectively to afford 4-acylpyrrole derivatives. On the other hand, treatment of the pyrroles with DDQ in the presence of AcOH furnished the corresponding 4-(1-acetoxyalkyl)pyrroles. The resulting 4-(acetoxymethyl)pyrrole reacted with various nucleophiles to afford the functionalized pyrrole derivatives in good yields.
An improved coupling procedure for the barton-zard pyrrole synthesis
作者:Pavel Bobál、David A. Lightner
DOI:10.1002/jhet.5570380239
日期:2001.3
final step in the Barton-Zard pyrrolesynthesis uses inexpensive potassium carbonate as base in the coupling-cyclization reaction of vic-nitro-acetates with isocyanides. In this modification the isolated yields of synthetically useful 2-carboalkoxypyrroles (1a,b and 3) and 2-(p-toluenesulfonyl)pyrroles (2a,b) consistently rise to the 78-89% range. Conversion of 2a to 5-(p-toluenesulfonyl)-2-pyrrolinone
Tosyl group of 3,4-disubstituted 2-tosylpyrroles easily rearranged from 2- to 5-position by treatment with TFA. The ratio of the regioisomers at equilibrium was definitely influenced by the bulkiness of the substituent at 3-position of the starting 2-tosylpyrroles.
An Intramolecularly Hydrogen Bonded Dihydrotripyrrinone
作者:Adrianne K. Tipton、David A. Lightner
DOI:10.1007/pl00010223
日期:1999.3
A yellow tripyrrole analog (1) of bilirubin has been synthesized, and its lone propionic acid group is found to engage in conformation determining, intramolecular hydrogen bonding in solution and in the crystal. Molecular modelling and X-ray crystallography reveal an abbreviated ridge-tile or L-shape conformation in which an essentially planar dipyninone is hydrogen bonded to the single opposing propionic acid group. In the (arbitrary) (P)-helicity ridge-tile, the torsion angles about C(10) are computed to be 55 degrees and 61 degrees by molecular dynamics and found to be 66 degrees and 53 degrees in the crystal. Such torsion angles lead to an interplanar dihedral angle (similar to 93 degrees) between the dipyninone and its adjoining pyrrole that is very close to the dihedral angle (similar to 98 degrees) found in intramolecularly hydrogen bonded bilirubin.