Sotolon (1) and maple furanone (2) are naturally occurring chiral furanones. These 5-substituted-2(5H)-furanones are industrially significant aroma compounds due to their characteristic organoleptic properties and extraordinarily low odor thresholds. Each enantiomer of 1 and 2 was successfully obtained by preparative enantioselective supercritical fluid chromatography. The absolute configuration of 1 was confirmed as (R)-(-)-1 and (S)-(+)-1 by adopting the vibrational circular dichroism (VCD) approach. The absolute configuration of 2, which has remained ambiguous since its discovery in 1957, was determined as (R)-(+)-2 and (S)-(-)-2 for the first time by the VCD technique. Surprisingly, the signs of the optical rotation of 2 are opposite of those of 1 regardless of their identical absolute configurations. This observation emphasizes the risk in absolute configurational assignments based on comparison of optical rotation signs of similar structures. Odor evaluation of the enantiomers of 2 revealed different odor intensities.
Enantiomeric pairs of mirror-image molecular structures are difficult to resolve by instrumental analyses. The human olfactory system, however, discriminates (−)-wine lactone from its (+)-form rapidly within seconds. To gain insight into receptor coding of enantiomers, we compared behavioural detection and discrimination thresholds of wild-type mice with those of ΔD mice in which all dorsal olfactory receptors are genetically ablated. Surprisingly, wild-type mice displayed an exquisite “supersensitivity” to enantiomeric pairs of wine lactones and carvones. They were capable of supersensitive discrimination of enantiomers, consistent with their high detection sensitivity. In contrast, ΔD mice showed selective major loss of sensitivity to the (+)-enantiomers. The resulting 108-fold differential sensitivity of ΔD mice to (−)- vs. (+)-wine lactone matched that observed in humans. This suggests that humans lack highly sensitive orthologous dorsal receptors for the (+)-enantiomer, similarly to ΔD mice. Moreover, ΔD mice showed >1010-fold reductions in enantiomer discrimination sensitivity compared to wild-type mice. ΔD mice detected one or both of the (−)- and (+)-enantiomers over a wide concentration range, but were unable to discriminate them. This “enantiomer odour discrimination paradox” indicates that the most sensitive dorsal receptors play a critical role in hierarchical odour coding for enantiomer identification.
Takasago has been devoted to producing l-menthol since 1954, and our long history of manufacturing this important aroma chemical is reviewed here. The current asymmetric catalytic process had its 30th anniversary in 2013. Our l-menthol process is considered carbon-neutral, and, therefore, 'green' and sustainable. It uses renewable myrcene obtained from gum rosin as a starting material. In addition, the Rh-BINAP (=2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) catalytic system is highly efficient. This pathway not only leads l-menthol, but a variety of 100% biobased aroma chemical products as well. By measuring the (14) C levels in a material, one can determine the percentage of carbon that is biobased. This biobased assay, described as the ratio plant-derived C/fossil-derived C, can clarify how renewable a product really is. This will be highlighted for several of Takasago's key aroma chemicals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.