FULL PAPER New, Sesquiterpenoid-Type Bicyclic Compounds from the Buds of Betula pubescens  Ring-Contracted Products of β-Caryophyllene? Karel D. Klika,* [a] Betül Demirci, [b] Juha-Pekka Salminen, [c] Vladimir V. Ovcharenko, [a] Satu Vuorela, [d] K. Hüsnü Can Bas ¸er, [b] and Kalevi Pihlaja [a] Keywords: Caryophyllenes / Natural products / NMR spectroscopy / Mass spectrometry / Sesquiterpenes / Structural elucidation The essential oils obtained from the buds of Betula pubescens ssp. pubescens and B. pubescens ssp. czerepano- vii were analyzed both by GC and GC/MS and, of the 31 compounds identified, 14-acetoxy-β-caryophyllene was de- termined to be the main component in both oils in addition to 25 other previously known compounds. Three of the com- pounds 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 lac- tone (1,4,4,8-tetramethyl-10-oxatricyclo[6.2.1.0 2,5 ]undecan- 9-one, hushinone), and the recently described 6-hydroxycar- yophyllene. The isolation of birkenal also enabled identifica- tion of its corresponding alcohol {(4,8,8-trimethyl-2-methyl- Introduction Betula sp. (Betulaceae), commonly known as birch, are trees or tree-like shrubs that are widespread in temperate regions of the northern hemisphere from Canada to Japan, and a characteristic feature of Betula species is their papery, white bark, which peels off easily. [1] Birch, in particular B. pendula, has long been medicinally important in many countries and cultures and practically all of the plant parts have been utilized for these purposes, but especially the leaves, tar, and essential oils have been used in traditional medicine to treat a wide variety of maladies, including skin and hair problems, infections, inflammations, rheumatism, arthritis, urinary-tract disorders etc. [2-4] Birch essential oils have also been used in cosmetic and hair products [5-7] and have been the subject of numerous investigations [4,5,8-13] [a] Structural Chemistry Group, Department of Chemistry, University of Turku, Vatselankatu 2, 20014 Turku, Finland [b] Department of Pharmacognosy, Faculty of Pharmacy, Anadolu University, 26470 Eskis ¸ehir, Turkey [c] Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, Vatselankatu 2, 20014 Turku, Finland [d] Food Chemistry, Department of Applied Chemistry and Microbiology, University of Helsinki, Latokartanonkaari 11, 00014 Helsinki, Finland Eur. J. Org. Chem. 2004, 2627-2635 DOI: 10.1002/ejoc.200300808  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2627 enebicyclo[5.2.0]non-4-yl)methanol, birkenol} and the acet- ate 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 β-caryophyllene or a derivative thereof. The fifth novel compound present in the oils was determined to be the acetate of 6-hydroxycaryophyllene. The preferred conforma- tions of the seven- or nine-membered rings in these struc- tures were also determined. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) over the years. As an extension of our ongoing investigation into the essential oils derived from birch species native to Turkey, [4,11-13] we have now investigated two species native to Finland, the mountain birch [Betula pubescens ssp. czere- panovii (Orlova) Hämet-Ahti] and the white birch (Betula pubescens ssp. pubescens Erhr.). The wood of both these tree species is utilized extensively as firewood, and white birch, to a limited degree, for furniture manufacture, whilst the leafy branchlets are traditionally employed as vihta (or va- sta) in the Finnish sauna ritual. Birch essential oils, unadul- terated or mixed with other essential oils, are also often used to create a more conducive atmosphere in this afore- mentioned practice by sprinkling them directly onto the hot stones or by their addition as a dispersion to the water which is splashed onto the stones. Birch essential oils are also used in a similar vein in aromatherapy and other anal- ogous practices which have achieved recent widespread popularity in Western culture. Thus, the exposure of man to birch compounds can be considerable either through direct contact or inhalation. Moreover, in the search for func- tional foods or food additives with desirable properties, par- ticularly antioxidant properties, many plants or their ex- tracts, including species not normally considered as food crops, have come under close scrutiny. [14] Herein we report the compositions in terms of the com- pounds present in the essential oils of the early-season buds