Oxidation of hydroxy-L-proline by periodate.

Some time ago Carter and Neville reported (1) that hydroxy-n-proline yields formaldehyde on oxidation with periodate. In another laboratory, this oxidation was found to produce a considerably lower yield of formaldehyde than we had obtained.’ A further study of this reaction was accordingly undertaken. Oxidation of several new samples of hydroxy-L-proline gave lower yields of formaldehyde than those previously obtained. To eliminate interference by possible contaminants, hydroxy-L-proline was purified through the 0, N-dibenzoyl derivative. This substance (not previously described) is a very satisfactory derivative for the purification and identification of hydroxy-L-proline. Under the proper conditions, the sodium salt precipitates from the benzoylation mixture in good yields. The free acid is readily purified and reconverted to hydroxy-L-proline. Material purified in this way was oxidized with varying quantities of periodate according to the procedure of Shinn and Nicolet (2). The results clearly indicate that the amount of formaldehyde formed depends critically on the molar ratio of periodate to amino acid. With a ratio of 5 moles of periodate to 1 of amino acid, an insignificant amount of formaldehyde was formed, while proportions of 10 : 1 and 20: 1 of the reactants gave 0.15 and 0.24 moles of formaldehyde, respectively. These variations were reflected by corresponding differences in the rate of oxidation of hydroxy-L-proline as measured by the rate of periodate consumption and the changes in optical activity of the solutions (see Tables I, II, III). These data show that the yield of formaldehyde is much less than that previously reported by us and that hydroxy-L-proline is not likely to interfere with the determination of serine by the methods of Nicolet and Shinn (3) and of Rees (4). In these procedures, the excess of periodate is not sufficient to produce an appreciable amount of formaldehyde from hydroxyproline, as is shown by the observation of Rees (4) that essentially equivalent amounts of volatile aldehyde and ammonia are produced in the oxidation of gelatin hydrolysates by periodate. No attempt has been made to describe the exact course of the oxidation