(Z)-α-Santalol, which has a unique woody odor, is a main constituent of sandalwood essential oil. We investigated the structure-odor relationship of (Z)-α-santalol and its derivatives, focusing on the relationship between the structure of the side chain and the odor of the compounds. Various α-santalol derivatives (aldehydes, formates, and acetates) were synthesized from (Z)- and (E)-α-santalol, which were prepared from (+)-3-bromocamphor through modifications of a reported synthetic route. The Z- and E-isomers of α-santalols have different double-bond configurations in the side chain. Analogues with saturated side chains were also prepared from the corresponding α-santalols, and the odors of the all the prepared compounds were evaluated. We found that the odors of the Z-isomers (woody) were similar to those of the corresponding saturated compounds, but clearly different from the odors of the corresponding E-isomers (odorless, fresh, or fatty). These results indicate that the relative configuration of the side chain with respect to the santalane frame plays an important role in the odor of α-santalol. E-configuration in the side chain eliminates the woody odor character of α-santalol and its examined derivatives, whereas the Z-configuration or saturation of the carbon side chain does not.

-Santalol is a sesquiterpene that is a major constituent of sandalwood (Santalum album L.), and is responsible for its distinctive woody odor. We replaced the polycyclic moiety and hydroxyl group of -santalol with other moieties, and we compared the odors of the E/Z-isomers and their saturated analogues. Our previous study of the structure-odor relationships of -santalols bearing hydroxyl, formyl, formyloxy, and acetoxy functional groups showed there was a similarity in odor between the Z-isomer and its saturated analogue. We synthesized -santalols with a benzyl group in place of the hydroxyl group, because many benzyl compounds have strong characteristic odors. We found similar odors for the E-isomer and its saturated analogue. In contrast, the odors of the santalol derivatives with a hydroxyl, formyl, formyloxy, or acetoxy group were different. We also replaced the bulky polycyclic moiety with a linear alkyl chain. The polycyclic moiety was the most important structural factor in the characteristic sandalwood odor. The synthesis of derivatives and the evaluation of their odor allowed us to identify the key structural factors in the odor of -santalol.

Determining the absolute stereochemistry of organic compounds in solution remains a challenge. We investigated the use of Raman optical activity (ROA) spectroscopy to address this problem. The absolute configurations of (+)-(R)-and (-)-(S)-limonene were determined by ROA spectroscopy, which can be applied to smaller amounts of sample as compared with vibrational circular dichroism (VCD) spectroscopy. This ROA method was also applied to (+)-(E)--santalol and shown to be successful in the determination of the absolute configuration of this compound. ROA spectroscopy shows promise as a useful tool for determining the absolute stereochemistry of many natural compounds.

The authors are sorry to report that some of the 13C-NMR data reported in their recently published paper [1] were incorrect. While this manuscript was in preparation and pending recording of some 13C-NMR spectra the data of α-santalol was used as a placeholder. Upon revising the manuscript according to the reviewers’ comments, they mistakenly thought that all spectral data had been replaced by the correct measured data. Consequently the authors wish to make at this time the following corrections to the paper