The chemistry fragrances

Neerav Shah 3rd Year Seminar February 22, 2001

Fragrance Chemistry
All civilizations, from antiquity to present time, have used fragrances for a variety of purposes. Before the advent of organic synthesis, fragrances were often limited to those found in the form of oils, balsams, exudates, and resins.1 With development of organic synthesis during the 19th Century, fragrance chemistry advanced into industrial synthesis and distribution. Since that time, a great deal has been achieved in both the understanding of the biology of smell, olfaction, as well as the development of new and unique fragrances. Biology of Olfaction Odorant binding proteins (OBPs) are small, water soluble proteins that are approximately 19 kDa in size.2 OBPs belong to a family of carrier proteins known as lipocalins and reversibly bind a variety of different odorants in the nM to µM range.2 The ability for OBP to bind such a wide array of odorants, as well as the selective localization in the lateral nasal cavity, suggest a physiological role in olfaction.3 Bovine OBP was crystallized as a homodimer in which the two subunits are held together by noncovalent bonds.4 Each monomer has an eight stranded β-barrel with an α-helix. In the dimer, the α-helix of one monomer completes the β-barrel of the other as shown in Figure 1. Based on a wealth of structure-activity relationship data, there are three

Figure 1. Crystal structure of Bovine OBP homodimer. possible roles OBP could play in the process of olfaction.5 The first would be to act as a buffer, lowering the concentration of odorants that bind to the olfactory receptors.6 This action would trap most of the molecules that would otherwise inactivate the olfactory receptors for a long period of time. A second role of OBP could be to serve as a carrier protein like the lipocalins.7 Most odorants are small hydrophobic molecules, poorly soluble in the aqueous mucus surrounding the olfactory receptors. OBP could bind odorants and transport them