3-Phenylpropanylcinnamate, a copolymer unit in Siegburgite fossil resin: a proposed marker for the Hammamelidaceae

Abstract

Siegburgite, an unusual Tertiary aromatic resin found near Bitterfeld (Germany), has been characterised earlier by FTIR spectrometry as polystyrene-like material. Here the molecular weight distribution of the soluble part is determined by size-exclusion chromatography (SEC) to be bomodal with maxima at 400 and 30,000 Da. Using combined gas chromatographic-mass spectrometric techniques (GC–MS) traces of oleanonic and 3-epi-oleanolic acid are found in the low MW fraction of Siegburgite. 3-Phenylpropanylcinnamate is detected in the high MW fraction by pyrolysis (Py)–GC–MS. Although also present in the soluble part of the high MW fraction, this compound is present especially in the insoluble residue, indicating that the ester is incorporated in the polymer chain. Oleanonic acid, 3-epi-oleanolic acid and 3-phenylpropanylcinnamate are constituents of commercially available Gum Storax from modern Liquidambar orientalis Mills. The proposed paleobotanical origin of Siegburgite from the Hammamelidacae family is thus chemically confirmed. In addition, a comparable polystyrene-like resin originating from North America (Squankum New Jersey) was compared to Siegburgite. The polystyrene matrix of this resin is comparable to that of Siegburgite, but no molecular markers confirming its origin could be found.