alpha-Phellandrene

The present work reports the chemical compositions, antibacterial and antioxidant activities of essential oils from T. jasminoides flowers collected from two different geographical areas, Chiang Rai and Chiang Mai, Thailand. The essential oil of T. jasminoides from the Chiang Rai area had 99 compounds representing 97.9% of the total oil composition, with E-nerolidol and α-phellandrene as the major constituents. In contrast, the essential oil of T. jasminoides collected from the Chiang Mai area contained 93 components representing 94.8% of the total oil, with trans-linalool oxide and citronellol as the major compounds. Flower oils of T. jasminoides exhibited greater antibacterial activities against Gram-negative bacteria than Gram-positive bacteria. Both oils displayed antioxidant activities.

There is a great interest in developing in vitro/in silico methods for the prediction of contact allergenic activity. However, many proposed methods do not take the activation of prohaptens to sensitizers by skin metabolism into account. As a consequence, consumer products containing potent sensitizers could be marketed. To identify prohaptens, studies regarding their structure-activity relationships and the mechanisms of their activation must be conducted. In the present investigation, we have studied the structure-activity relationships for alkene prohaptens. A series of seven alkenes (1-7), all of the same basic structure but with variation in the number and position(s) of the double bond(s), were designed and screened for sensitizing capacity using the murine local lymph node assay. Compounds 1-7 were also incubated with liver microsomes in the presence of glutathione to trap and identify reactive metabolites. The metabolic conversion of three alkenes (9-11) to epoxides (12-15) was also studied along with comparison of their sensitizing capacity. Our results show that conjugated dienes in or in conjunction with a six-membered ring are prohaptens that can be metabolically activated to epoxides and conjugated with GSH. Related alkenes containing isolated double bonds and an acyclic conjugated diene were shown to be weak or nonsensitizers. For the first time, the naturally occurring monoterpenes alpha-phellandrene, beta-phellandrene, and alpha-terpinene were demonstrated to be prohaptens able to induce contact allergy. The difference in sensitizing capacity of conjugated dienes as compared to alkenes with isolated double bonds was found to be due to the high reactivity and sensitizing capacity of the allylic epoxides metabolically formed from conjugated dienes. We recommend that these structure-activity relationship rules are incorporated into in silico predictive databases and propose that the prediction of contact allergenic activity of suspected prohaptens is based on assessment of susceptibility to metabolic activation and chemical reactivity of potential metabolites.