A novel synthetic route to heterogeneous acyloins was developed using benzothiazole/thiazolium species. The synthetic route mimics the biological action of thiamine pyrophosphate (TPP) in acetohydroxyacid synthase, the first enzyme of the valine-isoleucine biosynthetic pathway. The synthetic intermediates were examined by x- ray crystallography. Racemic [3,4-13C2]-α-acetolactate was synthesised. Treatment of the 13C-labelled α-acetolactate with acetolactate decarboxylase and analysis of the subsequent reactions by Hnmr showed that the enzyme rapidly decarboxylated the S-isomer to give [l,2-13C2]-3-hydroxy-butan-2-one and the R-isomer underwent an enzyme catalysed tertiary ketol rearrangement and then decarboxylation to yield [3,4-13C2]-3- hydroxybutan-2-one. The stereochemistry of a base-catalysed tertiary ketol rearrangement was investigated. R-α-acetohydroxybutyrate was treated with alkali and the resulting products were analysed by reaction with acetolactate decarboxylase. It was found that there is a preference for a syn-conformation of the C-0 bonds during the carboxylate ion migration. A novel sixteen step synthesis of methyl α-acetolactate with a chiral methyl group at the α-position was developed. Chemical syntheses of intermediates of the valine-isoleucine biosynthetic pathway were developed, including the attempted synthesis of trifluoromethyl-analogues. High field ‘Hnmr techniques were used to investigate directly the reactions catalysed by AHAS isoenzyme 2 (Salmonella tvphimurium) and AHAS isolated from pea plants. The ‘Hnmr investigations permitted the analogous reactions catalysed by AHAS to be studied and gave an insight into the nature of the reactions occurring at the enzyme active site.