Amberene and 1-methylamberene, isolated and identified from Kuji amber (Japan)

Abundant labdatriene derivatives, named amberene [15,19,20-trinor-5,7,9-labdatriene (or 1,6-dimethyl-5-isopentyltetralin) (1)] and 1-methylamberene [15,20-dinor-5,7,9-labdatriene (or 1,1,6-trimethyl-5-isopentyltetralin) (2)] were isolated from the methanol extract of Kuji amber by HPLC. The structures were elucidated by spectral analyses including EIMS, 1D and 2D NMR and some previous assignments corrected.