Synthesis and analysis of libraries of potential flavour compounds : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Palmerston North, New Zealand

Abstract

The goal of this project was to synthesise potential flavour compounds combinatorially and identify key components for further investigation as flavourants in dairy products. This thesis describes the design and synthesis of libraries of ketones and γ-lactones that will be evaluated for flavour potential. Gas chromatography-mass spectrometry (GCMS), the Fox, and gas chromatography-olfactometry (GC-O) were used throughout this study. Ketones were synthesised individually via a two-step sequence: a Grignard reaction followed by the oxidation of the resulting alcohol in Chapter 2. Some compounds selected from the Fox analysis were assessed by GC-O. The analysis gave promising results for aromatic and cyclopropyl ketones and a library of cyclopropyl ketones was prepared. Individual racemic lactones were synthesised via a two-step sequence: the Linstead modification of the Knoevenagel reaction and subsequent lactonisation in Chapter 3. Libraries of racemic γ-lactones (C8-C12), including α-substituted γ-lactones, were produced combinatorially. Further, synthesis of a library of γ-thionolactones was achieved by treatment of a library of γ-lactones with Lawesson's reagent. The libraries were analysed by GC-O. A (R)-dodecalactone was synthesised from L-glutamic acid and the (S)-enantiomer was synthesised by the same sequence from D-glutamic acid in Chapter 4. Asymmetric syntheses of both enantiomeric series of γ-lactones utilizing the Sharpless asymmetric dihydroxylation reaction was employed to give the libraries in Chapter 5. Libraries of a-substituted and β-substituted γ-lactones were synthesised combinatorially and analysed by GC-O.