/ Studies on Betula essential oils
Issue in Honor of Prof. Atta-ur-Rahman ARKIVOC 2007 (vii) 335-348 In the light of the recent accumulated data, we propose that 14-hydroxy-ß-caryophyllene is synonymous with a-betulenol formerly isolated by Treibs from the bud essential oil of B. lenta 8. The isolation of 14-hydroxy-ß-caryophyllene (1) was also reported by Macleod24 from Pterocaulon serrulatum (Montr.) Guillaumin, an Australian plant, supporting the previously reported data.23,25 We acetylated 1 to form 14-acetoxy-ß-caryophyllene (1a),13 which was also shown to be naturally present in Betula bud essential oils (0.1-0.8%) by GC-MS (Scheme 1). Consequently, we suggest that 14-acetoxy-ß-caryophyllene (1a) is synonymous with a-betulenol acetate, which was reported from B. lenta essential oil earlier.8 H H OH OAc (CH3CO)2O Pyridine, 600C HH 1 1a Scheme 1. Acetylation of 14-hydroxy-ß-caryophyllene (1). ß-Betulenal (2) which was isolated by MPLC from Betula essential oils was also synthesized. 13 ß-caryophyllene (3) was treated with SeO2, resulting in the formation of ßbetulenal (2), 14-hydroxy-isocaryophyllene (4), and isocaryophyllene (5), as seen in Scheme 2. Compound 2 and 4 were isolated individually from the reaction mixture followed by structures confirmation by 1H and 13C NMR. This information supported that 14-hydroxy-isocaryophyllene (4) is synonymous with ß-betulenol and ß-betulenal (2) with isocaryophyllen-14-al, when compared with previous investigations.8 To ensure the proposal, 2 was subjected to a mild reduction with NaBH4, resulting in ß-betulenol (4). These compounds were also detected in the Betula bud essential oils by GC-MS. Content of ß-betulenol and ß-betulenal, in the oils of investigated Betula species were found from trace to 1.2% and 2.0-5.2%, respectively (Table 1). H H H H R SeO2 EtOH 3 2 4 5 R= CHO R= CH2OH R= CH3 Scheme 2. Oxidation of ß-caryophyllene (3). ISSN 1424-6376 Page 337 ©ARKAT USA, Inc.
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