Muguet odour

Iso- 3-bisabolol (29) is also an example of pronounced odour differences between diastereoisomers and even enantiomers (Figure 14.5). Braun et al. (2003) separated the two diastereoisomers (29a and 29b) by HPLC and found that only 29a was odour active. GC smelling on a chiral column revealed that only one of the enantiomers of 29a possessed the strong, floral muguet odour and that the other enantiomer was odourless. The configuration of the active isomer was determined as (6R,7R) based on comparisons of retention time order with enan-tiomerically pure samples of (3-bisabolol (30). 

Figure 14.23 Structural requirements for a muguet odour in 3-alkylcycloalkanols...

A search is made for ingredients that have the desired odour characteristics. For the Business Scents Ltd brief, market research indicates that exotic, tropical, fruity and watery floral muguet notes... 

Each odour is smelled by the panellist, who then scores the perceived intensity of each odour character that she or he can detect (referring to the set of standard odour references for clarification if necessary), which results in a sensory profile for that odour. A minimum of at least 20 profiles is usually collected for each sample and an average profile is then calculated. A set of typical odour profiles is shown in Figure 8.3. These profiles show the differences in perceived intensity of 13 odour characteristics identified in seven perfume materials, and immediately it is possible to see that although all of the materials are floral or muguet in character, one material is far more fruity (cyclamen aldehyde) and another (Mayol ) is far more herbal than the other materials. 

Figure 8.3 Odour profiles of a selection of muguet perfumery materials Statistical Techniques...

In the sections above, the sensory profiling and multidimensional scaling techniques are illustrated using data obtained from the analysis of muguet perfumery materials. From a purely olfactory point of view, the type of odour that best fits the odour described in this brief is cyclamen aldehyde, but with the range of products that need to be considered in this brief the choice of material is not quite so simple. 

Since the blossom oil of lily of the valley is not commercially available, the perfumers have to rely on synthetic substitutes, such as hydroxy-citronellal (1), Lilial (3) and Bourgeonal (6) to create their muguet fragrances. The oldest lily of the valley odorants, hydroxycitronellal and cyclamen aldehyde (2) (Winthrop Chem. Corp., 1929), were discovered by chance. Serendipity still continues to play an important role. Anselmi et al. (1992) synthesized and organoleptically screened a series of 38 tetrahydropyranyl ethers. This class of compounds was chosen because of their ease of synthesis and purification, and because of their stability in alkaline media, conditions under which aldehydes tend to undergo aldol condensations. Two compounds (24 and 25) were described as having a white, floral odour reminiscent of hydroxycitro-... 

Another example of analogue synthesis dates back to the 1960s. As mentioned above, the first phenylpropanal to be discovered with a white, floral odour was cyclamen aldehyde, 3-(4-isopropylphenyl)-2-methylpropanal (2). As the name implies, its odour is reminiscent of wild cyclamen. However, at low concentrations the odour possesses a hydroxycitronellal-like note. Consequently, it was common practice in the 1960s to replace hydroxycitronellal, which is unstable in alkaline media and irritating to the skin, with cyclamen aldehyde. However, from an odour point of view the substitution was not entirely satisfactory. The discovery of the closely related r-butyl analogues (3 and 6) resulted in a certain improvement (Givaudan Corp., 1959 Boelens and Wobben, 1980). Both of these compounds have a more pronounced muguet floral odour. 

Where the branch is at a C atom further removed from the nucleus, the cyclamen character diminishes and the odour becomes more muguet [e.g. R1 = —CH2C(CH3)3]. 

The last was used by Boelens and Punter (1978) to quantify the odour quality of 16 muguet-smelling materials. These data were then used to derive equation (3), which related the odour similarity (OS) to molecular weight (MW) and the Kier connectivity index (A ). The concept of molecular connectivity was introduced by Randic (1975) and further elaborated by Kier and Hall (1976). It involves the calculation of numerical indices which describe the topology of a molecule. The Kier... 

Figure 13.10). The two binding sites were in similar areas of the protein. In both cases, the work involved molecular modelling rather than isolation and characterisation techniques and is therefore circumstantial. However, it is interesting to note that both molecules have similar muguet (lily of the valley) odours. 

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