New, sesquiterpenoid-type bicyclic compounds from the buds of Betula pubescens - Ring-contracted products of beta-caryophyllene?

Abstract

The essential oils obtained from the buds of Betula pubescens ssp. pubescens and B. pubescens ssp. czerepanovii were analyzed both by GC and GC/MS and, of the 31 compounds identified, 14-acetoxy-beta-caryophyllene was determined to be the main component in both oils in addition to 25 other previously known compounds. Three of the compounds were isolated from the oils and further characterized by NMR spectroscopy and mass spectrometry, including a new bicyclic aldehyde (4,8,8-trimethyl-2-methylenebicyclo[5.2.0]nonane-4-carbaldehyde, birkenal), a new tricyclic lactone (1, 4,4,8-tetramethyl-10-oxatricyclo[6.2.1.0(2,5)] undecan-9-one, hushinone), and the recently described 6-hydroxycaryophyllene, The isolation of birkenal also enabled identification of its corresponding alcohol {(4,8,8-trimethyl-2-methyl- enebicyclo[5.2.0]non-4-yl)methanol, birkenol} and the acetate of this alcohol {(4,8,8-trimethyl-2-methylenebicyclo[5.2.0]non-4-yl)methyl acetate, birkenyl acetate}, both of which are also novel compounds and are present in the two essential oils. These new compounds, bearing evident sesquiterpenoid traits, potentially arise biosynthetically as ring-contracted products of beta-caryophyllene or a derivative thereof. The fifth novel compound present in the oils was determined to be the acetate of 6-hydroxycaryophyllene. The preferred conformations of the seven- or nine-membered rings in these structures were also determined. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).