^{2nd Middle East Pharmacy and Pharmaceutical Conference}

GC-MS, GC-FID, NMR and microplate antimicrobial assay were used to examine the composition and bioactivity of the volatiles from the leaves of Physorhynchus chamaerapistrum Bioss in order to understand the chemical basis for using the leaves to treat ear infection. About 94% of the volatiles was a mixture of C4-C8 isothiocyanates (1-7) and strong absorption bands at 994 and 924 cm-1, respectively, confirmed the presence of aliphatic isothiocyanates, from which 3-butenyl isothiocyanate (4) was isolated as a major product (89.2%) followed by butyl isothiocyanate (3) (3.5 %),-caryohyllene (2.3%) and -gurjunene (1.5%) respectively. The structures of 4 and 2-methyl-3-butenoic acid (8), obtained from alkaline hydrolysis of the oil, were inferred from IR, MS, 1D and 2D NMR data. The oil and compounds 4 and 8 inhibited the growth of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Candida albicans at 313 g/ml and higher concentrations. This investigation lent support to the treatment of ear infection with volatiles from the leaves of P. chamaerapistrum and provides chemical evidence for classifying P. chamaerapistrum as an isothiocyanate chemotype and a Crucifer.