THE OXIDATION OF SULFUR-CONTAINING CYCLIC KETIMINES THE SULFOXIDE IS THE MAIN PRODUCT OF S-AMINOETHYL-CYSTEINE KETIMINE AUTOXIDATION

The products of autoxidation of S-aminoethyl-L-cysteine ketimine (AECK ) have been analysed with the amino acid analyzer, with thin layer chr omatography and with high performance liquid chromatography. Under the conditions of the assay (pH 8.5, 38-degrees-C, O2 bubbling) AECK is a lmost totally oxidized in 1.5 hours. Among the final products a compon ent running fast in HPLC, named Cx1, has been isolated, reduced with N aBH4 and analysed. Reduced Cx1 resulted to show the same properties of synthetic thiomorpholine-3-carboxylic acid-S-oxide, known in the past literature with the name of ''chondrine''. On the basis of these resu lts and by specific chromatographic tests, Cx1 has been identified as the sulfoxide of AECK. Among the other autoxidation products, thiomorp holine-3-one has been identified. The detection, after HCI hydrolysis, of glyoxylic acid and mesoxalic semialdehyde together with cysteamine indicates that compounds provided with easily cleavable S-C bonds, po ssibly thiohemiacetals or (and) thioesters, are the likely intermediat es for other products. AECK sulfoxide and thiomorpholine-3-one are rel atively stable and cannot be taken as the main intermediates for the r emaining oxidation products.