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Rational Odorant Design: Fantasy or Feasibility?

By: Charles Sell, Givaudan
Posted: September 12, 2008, from the September 2008 issue of P&F magazine.
The earliest successes were nature-identical materials such as coumarin, heliotropin and vanillin, all of which were used in 1889’s Jicky. Bertagnini’s aldehydes were already known at this time but it was their successful use in 1921 by Ernest Beaux (to provide a new top note character manifested in Chanel No. 5) that really stimulated the search for other novel fragrance ingredients.

There are many reasons why this search continues. In addition to originality of odor, cost, security of supply and performance in difficult media (such as laundry detergent), safety and sustainability are becoming increasingly important as plant-derived ingredients are being lost from the perfumer’s palette through unsustainable production (e.g., sandalwood, rosewood) or safety issues (e.g., sasafrass, fig leaf).

Screening of potential new ingredients requires time and involves expense in materials and equipment because in order for a material to pass an initial odor screen it is evaluated in a range of consumer products such as soap, laundry detergent, shampoo, conditioner, etc. Obviously, it is desirable to evaluate as few materials as possible and therefore the fragrance chemist will seek to synthesize only those materials with a high chance of passing the screening criteria. This is where rational design comes into play. Rational design uses our knowledge and understanding of fragrance in order to predict molecules with a better than random chance of making the grade as perfumery materials.

What must be taken into consideration when designing a novel fragrance ingredient?

The most obvious requirement for a fragrance ingredient is odor. Normally, a pleasant odor character is desired but there are quite a few widely used ingredients (e.g., indole) that few would describe as pleasant, and there are thousands of different pleasant odors that all find use. The same is true with tenacity, intensity and threshold; perfumers use ingredients across the scale for each. So, in terms of odor, there are no right or wrong answers, merely different blends of character, intensity, etc.

In contrast, in the field of safety, wrong answers are definitely possible. Any new substance that could harm production staff during manufacture, the consumer (when in use) or the environment (after use), will not survive the screening process. Substances that do not perform well in perfume formulae or in consumer goods will also be likely to fail in screening. Price is an important consideration because any new ingredient will be in competition with those already on the market and, unless it is more cost-effective than these, it will be unlikely to survive. Secondary benefits are not usually the cause of failure in screening but might well help a borderline material make it through the process to commercialization.