Advances in the Transition Metal (Rh, Ru)-Binap-Catalyzed Asymmetric Synthesis of Chiral Compounds for Flavours and Fragrances and their Associated Sensory Properties

Abstract

The variable biophysical responses to enantiomers are quite well documented in the field of medicine and human taste perception. For example, the l-form of ephedrine is effective against asthma but the d-form is not, and the d-form of aspartame tastes sweet, while the l-form bitter. Since the olfactory epithelium, like all biological tissues, is composed of bio-molecules consisting of L-amino acids and has a specific chiral environment, it should be able to distinguish one chiral molecule from its antipode. However, discussion on the olfactory differences of enantiomers has hitherto not been enthusiastic because it is difficult to obtain an enantiomerically pure material for olfactory evaluation. Furthermore, such discussions are problematical because the sense of smell is something abstract and more difficult to assess quantitatively than the other senses such as sight and sound.