Abstract:
C₁₃-norisoprenoids are a diverse class of carotenoid-derived aroma compounds that contributes to the aroma profile in grapes and wines. Glycosylated aroma precursors, namely the C₁₃-norisoprenoids glycosides are considered as a storage reserve for C₁₃-norisoprenoids, with the glycoside increasing the water solubility which then improves transport in plants. The glycosides are released through enzymatic activity and acid hydrolysis during wine fermentation. Previous syntheses of C₁₃-norisoprenoids and C₁₃-norisoprenoids glycosides are either non-stereospecific or lengthy, and not applicable to the preparation of labelled standards. This thesis focuses on the enantio- and stereospecific, and isotopically labelled stereospecific synthesis of blumenol B, 4,5-dihydrovomifoliol and icariside B₅, which are the most understudied C₁₃-norisoprenoids and C₁₃-norisoprenoids glycosides identified in grapes, wines and in other natural sources. Following these first total syntheses of blumenol B, 4,5-dihydrovomifoliol and icariside B₅, and their deuterated versions, the synthesised C₁₃-norisoprenoids and edulan were used as external and internal standards for the qualification and quantification of C₁₃-norisoprenoids in wines. For the first time, blumenol B and 4,5-dihydrovomifoliol were identified in Gewürztraminer and Riesling wine from New Zealand wine-growing regions. Quantum chemical electronic structure computations through density functional theory (DFT) determinations of the geometric and electronic structures of blumenol B and icariside B₅ in solvated systems provided complementary structural and energetic details for the prevailing identification of (S,R)- and (S,S)-blumenol B, and (S,R)- and (S,S)-icariside B₅ in nature.
