RESUMEN
Essential oils contain a large variety of volatile secondary metabolites such as terpenes, terpenoides, phenolic and aliphatic derivative. Nowadays, These compounds extensively used inPharmaceutical, sanitary and cosmetic industries. Antimicrobial activity of these oils and their components such as alpha-pinene and beta-pinene, the main essential oil constituent of some Hypericum spp., have been reported. This study was conducted to identify the constituents of essential oil in three Hypericum species in Iran to compare differences among their major volatile constituents. Essential oils were extracted by hydro-distillation of fresh plant materials using Clevenger apparatus. The essential oils were analyzed by both gas chromatography [GC] and gas chromatography ?mass spectrometry [GC-MS]. Monoterpens were found as the major constituent of essential oil in H. perforatum L. and H. patulum Thunb. However, n-alkans were the major constituent of the oil in H. tetrapterum Frise. In this study, alpha-Pinene [21.88%] was found to be the most abundant compound in the H. perforatum whilst beta- Pinene [30.20%] and n-undecane [30.84%] were the main constituents of H. patulum and H. tetrapterum essential oils respectively. In this study, we found that the different plant species made a remarkable difference in the essential oil constituents. In this study the most component of essential oils of H. perforatum and H. patulum were alpha-Pinene and beta-Pinene respectively and this component can be make them promising for treatment of infectious diseases such as infectious endocarditis