Issue in Honor of Prof. Atta-ur-Rahman ARKIVOC 2007 (vii) 335-348
Betula bud oil is also widely used in cosmetic products as a tonic and antiseptic mainly in hair products.4-7
Birch bark contains betulin, betulinol and a betuloside. The young leaves are rich in saponins and contain a diuretic flavonoid derivative (hyperoside), sesquiterpenes and tannins. The buds are rich in volatile oil. Birch tar contains creosol and guaiacol.5,8
The essential oils obtained from Betula species have been the subject of many investigations.7-12 Betulenol, the main component of the oil, was isolated and reported from Betula buds and named first as betulol by Soden and Elze in 1905. Its structure was tentatively elucidated as a bicyclic primary sesquiterpene alcohol. Further investigations on this molecule were conducted by Triebs and other researchers as compiled in a work of Guenther.5 Afterwards Treibs and Lossner reported a- and ß-betulenol, their acetates and a-betulenal by means of synthesis to support the chemical structures present in the essential oil of Betula lenta.8 In contrast, Holub reported the occurrence of a- and ß-betulenol, as well as a-betulenol acetate with different structures as the previous investigators, also isolated from Betula species.9 Dhar et al. reviewed the chemistry of the birch tree including the essential oil which appeared to support Holubs' previous work.10 Hiltunen and co-workers reconfirmed by means of chemical reactions and gas chromatography / mass spectrometry (GC - MS), the occurrence of the main compounds as a- and ß-betulenol and their relevant acetates in the bud oil of B. pubescens Ehrh., supporting Treibs’ work.11
Essential oil components of B. pendula were analyzed by Stepen and co-workers using GC where the main components were identified as a-betulenol acetate, caryophyllene and derivatives including low amounts of a- and ß-betulenol.12 Kaneko et al. reported betulenols and their acetates in the essential oils isolated from the buds of nineteen Betula species.7 Studies on the essential oils and sesquiterpenes of Betula species growing in Turkey were subject to several studies by our group.13-18
This present work covers the essential oil chemistry as well as biological activities of the main components isolated from various Betula species investigated by our group.
Results and Discussion
Caryophyllene and its derivatives have been of special interest in the field of natural products chemistry and subjected to many detailed works and reviews.19-22 There have been many conflicts and disagreements concerning absolute configurations and structures of caryophyllene derivatives isolated from natural sources.7-9,23
The buds of B. pendula, B. litwinowii and B. medwediewii collected from various parts of Turkey were hydrodistilled while B. browicziana and B. recurvata buds were subjected to simultaneous distillation-extraction method (SDE) using a Likens-Nickerson apparatus due to limited plant material. The bud oils were analysed by GC-MS. The main component was isolated by Medium Pressure Liquid Chromatography (MPLC) in high purity.13,16 Literature search and comparison with spectral data23 confirmed the identity of this compound as 14-hydroxy-ßcaryophyllene (1), which was found 20.5-37.5% in all investigated oils.
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