The molecular composition of Cretaceous ambers: Identification and chemosystematic relevance of 1,6-dimethyl-5-alkyltetralins and related bisnorlabdane biomarkers

One of the major components of the organic solvent extractable fraction of Cretaceous ambers is 1,6dimethyl-5-isopentyltetralin, a compound that has been incorrectly or not identified in previous reports on the molecular composition of Cretaceous ambers. Here, the purification and structural identification of 1,6-dimethyl-5-isopentyltetralin is reported from amber samples of the Cretaceous Penacerrada II deposit at Penacerrada, Alava (Basque-Cantabrian Basin, Spain). The structural identification of 1,6-dimethyl-5-isopentyltetralin allowed the complete identification of related compounds, comprising the family of 1,6-dimethyl-5-alkyltetralins. This suggests that those compounds, with concentrations up to 27% of the total organic extract of amber from Penacerrada, are characteristic for labdane-type biomarkers in Cretaceous fossil resins and their distributions indicate different compositional families, related to their botanical and topographic origin. Also, the name amberene is proposed for the main molecule of this group. The relative proportion of the amberene-type compounds suggests three compositional families for the Cretaceous Spanish ambers. (C) 2015 Elsevier Ltd. All rights reserved.