C13-Methylation of methyl pheophorbide a and stereoselective preparation of methyl (13R)-methylpyropheophorbide a |
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Authors: | Shin Ogasawara Hitoshi Tamiaki |
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Institution: | Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan |
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Abstract: | The (132R)-methoxycarbonyl group of methyl pheophorbide a, one of the chlorophyll-a derivatives, was converted to a methyl group through methylation at the C132 position followed by removal of the methoxycarbonyl group. The methylation of the C132 carboanion gave a 4:1 mixture of methyl 132-methyl-pheophorbide a and its 132-epimer. The successive pyrolysis of the major methylated product afforded methyl (132R)-methyl-pyropheophorbide a with a small amount of its (132S)-epimer. The substitution effects at the C132 position including stereochemistry were discussed on the basis of 1D/2D NMR, UV–vis absorption, and circular dichroism spectroscopic analyses as well as molecular modeling simulation. |
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Keywords: | Chlorophyll Epimerization β-Ketoester Stereochemistry Pyrolysis |
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