3alpha-O-Malonyl-12beta-O-acetyl-25-hydroxy-(20S,24R)-epoxydammarane (papyriferic acid) and two previously unknown dammarane triterpenes were identified from diethylether extracts of bark resin from juvenile Betula pendula. H-1 and C-13 NMR spectroscopy showed that a compound appearing often in chromatographic analyses in amounts comparable with papyriferic acid is its 3beta-epimer. The third compound which is abundant in individuals with low levels of the other two compounds was shown to be 3beta-O-malonyl-12beta-O-acetyl-20(S)-hydroxydammar-24-ene (pendulic acid), i.e. an analogue of the 3beta-epimer of papyriferic acid with open and partially reduced C-17 side chain.
Taipale, H., Vepsäläinen, J., Laatikainen, R., Reichardt, P., & Lapinjoki, S. (1993). Isolation and structure determination of three triterpenes from bark resin of juvenile European white birch. Phytochemistry, 34(3), 755 - 758. https://doi.org/10.1016/0031-9422(93)85354-T