Pyrroles and related compounds. Part 39. Structural and biosynthetic studies of the Chlorobium chlorophylls-660 (bacteriochlorophylls c). Incorporations of methionine and porphobilinogen

Abstract

Treatment of the phaeofarnesins (4) isolated from the Chlorobium chlorophylls-660 (ex. Chloropseudomonas ethylicum) with sulphuric acid in methanol gives the methyl phaeophorbides (1) which can be dehydrated by refluxing in benzene in the presence of acid to afford the 2-vinyl derivatives (2); prolonged refluxing gives the novel cyclised compounds (6). By-products from handling the pigments are the 8′-acetylbilitrienes (5), obtained by photo-oxygenation. [¹⁴CH₃]-, [¹³CH₃]-, and [¹³C²H₃]-L-methionine are efficiently incorporated into the Chlorobium chlorophylls-660, showing that the extra methylation present in the δ-methyl, 4-isobutyl, 4-n-propyl, and 5-ethyl groups of these pigments is methionine derived. Using 6-¹⁴C labelled material, porphobilinogen is also confirmed as an important building block in these bacterial chlorophylls.