Chemical Conversions of Natural Precursors

The reasons to use raw materials from renewable resources can be various. When a natural flavour ingredient has to be prepared, a natural raw material is essential, and natural raw materials are renewable, because they come from plants, animals or fermentation. For nature-identical flavour ingredients, a renewable raw material can be a good choice from a chemical point of view and quite often also from a cost point of view if turpentine is readily available in a country with limited or no petrochemical resources, -pinene from the renewable source is cheaper than chemically synthesised -pinene. A manufacturer chooses only for sustainable production if it is remunerative and at least as attractive as other options. 

Estimation of the volume of renewable resources involved in the flavour industry is very difficult. It is assumed that the total flavour and fragrance market 

In this chapter chemical conversions of natural precursors resulting in flavour chemicals are discussed. The main groups of natural precursors are terpenes for all kinds of terpene derivatives, vanillin precursors like lignin and eugenol, sugars for Maillard-associated flavour chemicals, amino acids and molecules obtained by fermentation or available as residual streams of renewable resources. 

Terpenes as Renewable Resources for Terpene Flavour Molecules 

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Chemical Conversions of Natural Precursors Obtained by Fermentation or from Residual Streams... 

P. H. van der Schaft, Chemical Conversions of Natural Precursors. In Flavours and Fragrances Chemistry, Bioprocessing and Sustainability R. G. Berger, Ed. Springer-Verlag Berlin, 2007 pp 285-301. 

This same increase in the number of isomers with molecular weight also applies to the other molecular types present. Since the molecular weights of the molecules found in petroleum can vary from that of methane (CH4 molecular weight = 16) to several thousand (Speight, 1999, and references cited therein), it is clear that the heavier nonvolatile fractions can contain virtually unlimited numbers of molecules. However, in reality the number of molecules in any specified fraction is limited by the nature of the precursors of petroleum, their chemical structures, and the physical conditions that are prevalent during the maturation (conversion of the precursors) processes. 

Many products from the flavour industry are primary products from renewable resources or secondary products obtained by chemical conversions of the primary products. In general these secondary products are key flavour chemicals with a high added value. The cost diiference between a precursor, the primary product and the flavour chemical can easily amount to a factor 20-1,000, especially when it concerns a natural flavour chemical. A large part of this cost reflects, of course, the efficiency of the reaction, the labour involved and the cost of the other reagents. 

The route could start from the mixture of cis- and /rans-communic acids (or also from other diterpenes, such as isocupresic acid). The isolation of hydroxyacid I as a natural product from Acrostalagmus reinforces the possiblity of the existence of diene II as a key precursor, not only of isoacrostalidic acid and acrostalidic acid, but also of dilactone III. The straightforward chemical conversion of I into III in a recent publication by Barrero et al. [20] supports this hypothesis. 

Chemical methods for the production of enantiomerically pure a-amino acids have been extensively investigated in recent years.3 Conversely, there are relatively few methods for the synthesis of chiral, nonracemic p-amino acids,4 although there is considerable interest in these compounds as precursors to p-lactams,5.6 as components of natural products,7 and as reactive molecules in their own right.8... 

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