Isolation of yeast Ca2+ signal transduction inhibitors from the Early Cretaceous Burmese amber

Two kinds of biologically active compounds were isolated from the MeOH extract of the Early Cretaceous Burmese amber [99 million years ago (Ma)], which is older than the K-Pg boundary (65 Ma). These compounds had inhibitory activity against the hypersensitive mutant yeast strain (zds1∆ erg3∆ pdr1∆ pdr3∆) with respect to Ca²⁺ signal transduction. They were identified as 16,17-bisnordehydroabietic acid (1) and 16,17-bisnorcallitrisic acid (2), respectively, on the basis of spectral analyses including HREIMS, 1D, and 2D NMR. Both have faint growth restoring activities around the clear inhibition zone against the mutant yeast on the 0.31-0.16 μg/spot. This is the first report of direct structural elucidation of 1 and 2 and the biologically active compounds derived from Burmese amber.