Issue in Honor of Prof. Atta-ur-Rahman ARKIVOC 2007 (vii) 335-348
Manns and Hartmann reported (4E)-isocaryophyllen-14-al (=ß-betulenal) in Cunila spicata Benth. (Lamiacea).26 Barrero et al.27 and Hiede et al.28 reported the presence of betulenal in Juniperus oxycedrus and J. virginiana essential oils without its configuration. Kaiser and Lamparsky29 assigned the structure of the aldehyde, formed in the reaction mixture by direct oxidation of caryophyllene with SeO2, as caryophyllen-14-al (=a-betulenal), which was also detected in lavender oil.
With the same intention as above we acetylated 14-hydroxy-isocaryophyllene (4), resulting in the formation of 14-acetoxy-isocaryophyllene (=ß-betulenol acetate) (4a). However, the acetate 4a was not detected in any Betula essential oils investigated in this study (Scheme 3).
H H CH2OH H H CH2OAc (CH3CO)2O Pyridine, 600C 4 4a
Scheme 3. Acetylation of 14-hydroxy-isocaryophyllene (4).
Furthermore, 14-hydroxy-ß-caryophyllene (1) was epoxidized by m-CPBA resulting in the formation of the two synthetic diastereomeric epoxides namely, 14-hydroxy-4,5-epoxy-ßcaryophyllene (ßa) (6) and 14-hydroxy-4,5-epoxy-ß-caryophyllene (ßß) (7), as shown in Scheme 4.16 These compounds were shown to be present in the investigated Betula essential oils (Table 1). 14-Hydroxy-4,5-epoxy-ß-caryophyllene (ßa) (6) was also obtained from the bud essential oil of B. pendula by MPLC. The acetate of this compound (6a) was shown to be present in the composition of the investigated Betula essential oils. The acetate of ßß-form (7a) was also found in essential oil of B. recurvata leaves in trace amounts (Table 1).
H H OH H H O R H H O R m-CPBA MeOH, 00C 16 R= CH2OH 7 R= CH2OH 6a R= CH2OAc 7a R= CH2OAc
Scheme 4. Epoxidation of 14-hydroxy-ß-caryophyllene (1).
In vitro antimicrobial activity evaluation against selected human pathogens Escherichia coli, Staphylococcus aureus, Micrococcus luteus, Pseudomonas aeruginosa, Bacillus cereus and the fungus Candida glabrata using 14-hydroxy-ß-caryophyllene (1), 14-acetoxy-ß-caryophyllene (1a), ß-betulenal (2), ß-caryophyllene (3), and 14-hydroxy-isocaryophyllene (4) were conducted. Chloramphenicol was used as reference and moderate activities were observed against Gram
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