The carbon-13 and proton NMR spectra of the methyl pheophorbides 6, methyl 2-vinylpheophorbides 2, methyl mesopheophorbides 7, and other degradation products from the green sulfur bacterium Chloropseudomonas ethylicum are described and assigned. In order to clarify certain spectra, model chlorins substituted with n-propyl, isobutyl, propenyl, and isobutenyl side chains are synthesized from the chlorophyll b degradation product, rhodin gj trimethyl ester (17). Successful separations of the homologous mixture of pheophorbides, using reverse-phase high-performance liquid chromatography, are detailed; only four major bands (rather than the six obtained from Chlorobium thiosulfatophilum cultures) were observed, and only a minute amount of 4-ethyl-5-methylpheophorbide (band 6) was apparent in the C. ethylicum culture presently being studied.
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Smith et al. (1980) studied this question.