The reaction between medium and long chain fatty acyl thioesters and neutral hydroxylamine results in the formation of acyl hydroxamic acids. Separation and identification of acyl hydroxamates is facilitated by conversion of these compounds to their acetyl derivatives. Thin-layer chromatoplate and solvent systems are described which permit the separation of the acetyl acyl hydroxamates on the basis of degree of unsaturation and on the basis of chain length (C6-C 18).
The quantitation of acyl thioesters, acyl chlorides, acyl phosphates, and acid anhydrides is readily accomplished by reacting these compounds with neutral hydroxylamine and measuring the red to purple color that is formed when the resulting acyl hydroxamates are reacted with a FeCl3 reagent, according to the method of Lipmann and Tuttle (1). Although it has been possible to separate and identify short chain acyl hydroxamates by paper chromatography (2,3) and by thin-layer chromatography (4), the separation of medium to long chain acyl hydroxamates has not been achieved. In an earlier report from this laboratory we showed that long chain acyl hydroxamates can be identified after conversion to the acetyl derivatives which are subjected to gas-liquid chromatography (5). In this procedure, however, the acetyl acyl hydroxamates are converted to isocyanates during the chromatography step, and the original acyl hydroxamates are lost.
Studies of the biosynthesis of long chain fatty acids have involved the identification of various chain length intermediates which are saturated, unsaturated, hydroxy-, and keto-fatty acyl groups attached covalently as thioesters to specific proteins of the fatty acid synthetase (5). Such iden-