The fragrance of Santalum album L. (sandalwood) has been used as a sedative. However, few reports have investigated the anxiolytic activity of sandalwood fragrance. Therefore, in this study, we examined the anxiolytic-like activity of hexane-extracted sandalwood oil (SAO). Male ICR mice, aged 5 weeks at the start of each experiment, were used. To mimic its clinical use, the effect of SAO after stress loading was investigated. Mice were individually housed in cages for 1 week and subjected to loaded water-immersion stress for 24 h. Next, SAO inhalation (i.h.) was initiated 90 min prior to the elevated plus maze (EPM) test. As a result, significant anxiolytic-like activity was observed at 4 μl/l air SAO i.h. In contrast, anxiolytic-like activity was not observed in non-stressed control mice. Additionally, mice were subjected to SAO i.h prior to water-immersion stress for 24 h in order to investigate its prolonged effect. As a result, significant anxiolytic-like activity was observed at 4 μl/l air SAO i.h. In contrast, anxiolytic-like activity was not observed in non-stressed control mice. The above results indicate that the anxiolytic-like activity of SAO i.h. is revealed under stress conditions and is prolonged for at least 24 h. Since the main components of SAO are (Z)-α-santalol (51.1%) and (Z)-β-santalol (28.5%), it is proposed that they are involved in mediating the characteristic anxiolytic-like activity of SAO.

The fruit of Illicium verum Hook. f. (star anise) is used by many as a spice. The fragrance of I. verum fruit is characteristically anise-like. In this study, hexane-extracted I. verum fruit oil (IVO), trans-anethole as the main component, and related compounds (propiophenone, 4'-methoxy-propiophenone, trans-β-methylstyrene) were analyzed in order to clarify the emotional effect of inhaling the fragrance of I. verum fruit. As a result, although 4 μL/L air IVO did not exhibit an anxiolytic-like effect, 1 μL/L air trans-anethole exhibited a significant effect (p < 0.05). Moreover, the anxiolytic-like effect of 1 μL/L air trans-anethole was significantly greater than 1 μL/L air propiophenone and 1 μL/L air 4'-methoxy-propiophenone (p < 0.05). Thus, the anxiolytic-like effect of trans-anethole was confirmed, and it is proposed that the methoxyl group and 1-propenyl group in the para position of the benzene ring are necessary for the effect.

Star anise is an important fragrance material that has a characteristic anise-like odor. Although the main component of star anise is (E)-anethole, which accounts for over 90% of the constituents, the odor of (E)-anethole is different from that of the material itself. Here, we examined the aroma profile of star anise. GC-MS analysis of star anise extracts showed that it contains many compounds with structures similar to (E)-anethole. Our results indicate that (E)-anethole is the key compound in the odor of star anise, but structurally similar compounds play an important role in creating its odor. We examined the structure-odor relationship of (E)-anethole, focusing on the methoxy and 1-propenyl substituents. Altering the 1-propenyl group changed the odors of all the anethole derivatives. Replacing the methoxy group with a hydrogen atom created compounds with similar fatty odors. This shows that the methoxy group is important for the characteristic odor of anethole. We synthesized anethole derivatives where the methoxy group was replaced with a methyl group. In both methoxy-and methyl-substituted anethole derivatives, altering the 1-propenyl group changed the odors of the derivatives. Therefore, the methoxy and methyl benzene moieties are important structural features for the odor of star anise. The structural characteristics of anethole are closely related to its odor expression.