| Autor: |
Boiadjiev, Stefan E., Holmes, Darren L., Timothy Anstine, D., Lightner, David A. |
| Zdroj: |
Tetrahedron; September 1995, Vol. 51 Issue: 39 p10663-10678, 16p |
| Abstrakt: |
A sterically congested analog of bilirubin with propionic acid groups replaced by pivalic acids (1) was synthesized from methyl 3-(2,4-dimethyl-5-ethoxycarbonyl-lH-pyrrol-3-yl)-2-methylpropionate (8). UV-visible and NMR spectroscopic analyses of 1 suggest intramolecular hydrogen-bonding and a preference for a ridge-tile conformation. The activation parameters for MP conformational inversion of 1 were determined by dynamic NMR analysis to be ΔH‡ 19.7 ± 1.4 kcal/mole and ΔS‡ + 10.4 ± 4.5 eu. Molecular dynamics computations predict a global energy minimum for a somewhat more open ridge-tile conformation as compared with bilirubin. Circular dichroism of the pigment complex with human serum albumin gives a bisignate Cotton effect: Δε431max = −51, Δε382max = +30, with the opposite signed order as compared with that found for the parent mesobilirubin-XIIIα: and bilirubin. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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