25th International Meeting on Organic Geochemistry IMOG 2011

P-071
Structural characterization of 1,6-dimethyl-5-isopentyltetralin
from Cretaceous conifer fossil resins and coals: a novel
diterpene biomarker
Cesar Menor-Salvan 1 , Marta Ruiz-Bermejo 1 , Bernd R.T. Simoneit 2
1 Centro de Astrobiologia (INTA), Torrejon de Ardoz, Spain, 2 Department of Chemistry, Oregon State
University, Corvallis, United States of America (corresponding author:menorsc@cab.inta-csic.es)
Recently, the gas chromatographic-mass
spectrometry (GC-MS) study of the individual
components of Cretaceous ambers (fossil resins)
shown the presence of a previously unidentified
compound with a molecular peak at m/z 230 (Pereira
et al. 2009; Menor-Salvan et al. 2010). This
compound, one of the main components of the
extractable fraction of amber, is also common in the
associated sediments, plant fossils and coals of the
amber deposit.
These authors suggested a 2,5,6-trimethyl-1butyltetralin
structure for the molecule, interpretation
based largely in the fragmentation pattern observed in
mass spectrum. In order to confirm this structure, we
carried out the isolation and purification of the
molecule from amber of the Cretaceous deposits
located at Basque-Cantabrian Basin (Cantabria,
Spain). For purification, the crude amber extract was
fractionated by sequential elution in silica gel column
followed by semi-preparative high performance liquid
chromatography of the fraction containing the target
compound and purity testing using GC-MS.
The pure compound, a colorless oil, was then
characterized by nuclear magnetic resonance (NMR).
Using the NMR and fragmentation data, we could
infer a 1,6-dimethyl-5-isopentyltetralin structure (Fig.
1) for the unknown compound, discarding the
structure previously suggested in the literature.
Fig. 1: Structure of 1,6-dimethyl-5-isopentyltetralin,
isolated from Cretaceous amber.
The biochemical precursors of this molecule are not
identified, but taking into account the structures
identified in the amber extracts and the preservation
of original biomolecules, the origin of the 1,6-dimethyl-
5-isopentyltetralin could be the oxidative degradation
of diterpenoids of the labdane class, as communic or
agathic acids. The association with conifer fossil
resins and the possible diterpene precursor suggest a
coniferous botanical origin. Therefore, the presence of
1,6-dimethyl-5-isopentyltetralin in the sedimentary
record could be indicative of conifer resin contribution
to the organic matter.
Spectroscopic characterization:
1 H NMR (CDCl3, 400 MHz) δ 6.97 (s, 1H), 6.96 (s,
1H), 2.89 (m, 1H), 2.70 (m, 2H), 2.55 (m, 2H), 2.27 (s,
3H), 1.88 (m, 2H), 1.67 (m, 1H), 1.34 (m, 2H), 1.27 (d,
J=7.02 Hz, 3H), 0.97 (d, J=6.25 Hz, 6H)
13 C NMR (CDCl3, 100 MHz) δ 140.3, 139.7, 134.8,
133.3, 127.8, 126.0, 38.2, 33.1, 31.1, 29.2, 27.4, 26.8,
23.6, 22.7, 20.8, 19.8.
EI-MS m/z (%) 230 (M + , 25), 215 (M-CH3, 14), 173
(29), 159 (100), 143 (13), 128 (12), 115 (7).
References:
Pereira, R., de Souza Carvalho, I., Simoneit, B.R.T.,
de Almeida Azevedo, D., 2009. Molecular
composition and chemosystematic aspects of
Cretaceous amber from the Amazonas, Araripe and
Recôncavo basins, Brasil. Organic Geochemistry 40,
863-875.
Menor-Salvan, C., Najarro, M., Velasco, F., Rosales,
I., Tornos, F., Simoneit, B.R.T., 2010. Terpenoids in
extracts of Lower Cretaceous ambers from the
Basque-Cantabrian basin (El Soplao, Cantabria,
Spain): Paleochemotaxonomic aspects. Organic
Geochemistry 41, 1089-1103.
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