Background: New prophylactic and therapeutic tools are needed for the treatment of herpes simplex virus infections. Several essential oils have shown to possess antiviral activity in vitro against a wide spectrum of viruses. Aim: The present study was assess to investigate the activities of the essential oil obtained from leaves of Artemisia arborescens against HSV-1 and HSV-2 Methods: The cytotoxicity in Vero cells was evaluated by the MTT reduction method. The IC₅₀ values were determined by plaque reduction assay. In order to characterize the mechanism of action, yield reduction assay, inhibition of plaque development assay, attachment assay, penetration assay and post-attachment virus neutralization assay were also performed. Results: The IC₅₀ values, determined by plaque reduction assay, were 2.4 and 4.1 μg/ml for HSV-1 and HSV-2, respectively, while the cytotoxicity assay against Vero cells, as determined by the MTT reduction method, showed a CC₅₀ value of 132 μg/ml, indicating a CC₅₀/IC₅₀ ratio of 55 for HSV-1 and 32.2 for HSV-2. The antiviral activity of A. arborescens essential oil is principally due to direct virucidal effects. A poor activity determined by yield reduction assay was observed against HSV-1 at higher concentrations when added to cultures of infected cells. No inhibition was observed by attachment assay, penetration assay and post-attachment virus neutralization assay. Furthermore, inhibition of plaque development assay showed that A. arborescens essential oil inhibits the lateral diffusion of both HSV-1 and HSV-2. Conclusion: This study demonstrates the antiviral activity of the essential oil in toto obtained from A. arborescens against HSV-1 and HSV-2. The mode of action of the essential oil as antiherpesvirus agent seems to be particularly interesting in consideration of its ability to inactivate the virus and to inhibit the cell-to-cell virus diffusion.

Using cytotoxicity against KB cancer cells as a lead, bioguided-fractionation of the petroleum ether and ethyl acetate extracts of Bituminaria morisiana leaves led to the isolation of two new pterocarpans, namely 3,9-dihydroxy-4-(3,3-dimethylallyl) [6aR, 11aR]-pterocarpan, 3-hydroxy-4-(3,3-dimethylallyl)-4′′,5′′-dehydropyrano[8,9:2′′,3′′][6aR,11aR]-pterocarpan and one new isoflavone identified as 4′,5′′-dihydroxy-6′′-methoxy-4′′,4′′-dimethyl-4′′,5′′-dihydro-6′′H-pyrano[2′′,3′′:7,8]-isoflavone. Moreover, two known pterocarpans, erybraedin C and bitucarpin A, three known isoflavones, daidzein, 8-prenyldaidzein and bidwillon C, one known furocoumarin, pseudoisopsoralen and one known coumestan, coumestrol were isolated. The structures of the isolated compounds were established by means of 1D and 2D NMR spectroscopy, as well as mass spectrometry. Further cytotoxicity tests against cells related to the immune system (Jurkat T, Mono-Mac-6 and polymorphonuclear cells) showed a moderate activity of the known pterocarpan erybraedin C against all cell lines used (IC₅₀ values between 17.6 - 28.8 μM). In addition, erybraedin C was found to induce necrosis in leukaemia Jurkat T cells.