Isolierung und charakterisierung der p-hydroxy-β-(carboxy-methyl)-zimtsäure (sphagnumsäure) aus der zellwand von Sphagnum magellanicumBrid.

The cell walls of numerous Sphagnum species are stained intensively red by Millon's reagent. The main Millon-positive component of Sphagnum magellanicum was identified as p-hydroxy-β-(carboxy)-cinnamic acid (fig. 1, Tutschek et al., 1973). In the present work the isolation procedure and the characterization of the phenolic substance are reported. The compound is extracted from green Sphagnum magellanicum by ethanol at ambient temperature. The separation and purification of the extract are performed on cellulose columns and thin-layers. Finally pale-yellow crystals are obtained which prove to be chromatographically homogeneous. The crystalline natural substance is called sphagnum acid. The chromatographical data of the sphagnum acid (tab. 1), the IR-spectrum (fig. 5) and the properties during the melting process are discussed with respect to the structure of the compound. Hydrolysis experiments under acidic conditions (tab. 2) indicate that the crystalline sphagnum acid is not a glycoside. The influence of alkali on the sphagnum acid is studied in comparison with the acidic hydrolysis reactions (tab. 3). In the sodium hydroxide melt (350°C) the natural substance is completely decomposed to p-hydroxy-benzoic acid but under solvolytic conditions (100°C) it remains unchanged. Analogous reactions are shown by p-hydroxycinnamic acid which has the same structural features as the sphagnum acid. The alkaline decomposition of the natural substance is in accordance with the structure of a p-substituted phenol. Concerning the isolation procedure for Czapek's sphagnol (Czapek, 1899) the reaction of the sphagnum acid is examined with sodium hydroxide solution under pressure. The cell wall material is decomposed by this treatment to sodium formiate which represents the purified form of the sphagnol crystals (Rudolph, 1972). Formiate, however, is not detectable after decomposition of the sphagnum acid under identical conditions. This result clearly demonstrates that there is no relationship between the sphagnum acid and the sphagnol crystals. The mild conditions of the extraction procedure support the view that the Millon-reaction in situ is mainly caused by the sphagnum acid. In this connection the native structure of the natural substance is discussed. This problem becomes evident by the fact that the phenolic substance is isolated as a free acid whereas cinnamic acids frequently occur as glycosides or esters in the plant kingdom (Geissman and Crout, 1969). Neither a glycosidic nor an ester bonding, however, can be split by ethanol under neutral conditions. For the same reason the sphagnum acid is no degradation product of a polymeric molecule, for instance lignin. A structural alteration of the alcohol-soluble substance in the course of the isolation procedure can be excluded experimentally. On the basis of these results it may be concluded that the sphagnum acid represents a native constituent of the cell wall. Es wird ein Aufarbeitungsgang beschrieben, durch den die Hauptkomponente der alkohollöslichen Millon-positiven Substanzen aus der Zellwand von Sphagnum magellanicum, p-Hydroxy-β-(carboxymethyl-)zimtsäure (Abb. 1, Tutschek et al., 1973), in kristalliner Form chromatographisch einheitlich isoliert werden kann. Das als Sphagnumsäure bezeichnete Phenolderivat wird durch seine physikalisch-chemischen Eigenschaften, Hydrolyse- und alkalischen Abbaureaktionen charakterisiert. Die experimentellen Daten stehen im Einklang mit der Struktur des Naturstoffs. Es wird gezeigt, daß zwischen der Sphagnumsäure und dem Czapek-schen Sphagnol (Czapek, 1899) kein Zusammenhang besteht. Aufgrund der schonenden Extraktions- und Isolierungsbedingungen kann angenommen werden, daß die Sphagnumsäure in der Zellwand weder glykosidisch noch esterartig gebunden ist, sondern einen in freier Form vorliegenden nativen Bestandteil der Zellwand darstellt.