Abstract
The non-protein nitrogen, or residual nitrogen of copy's milk is known to consist in part of urea, uric acid, creatinine, amino acids, and purine bases. The remainder is composed to a large extent of compounds of unknown structure. We wish to report that one of these heretofore unidentified substances of the residual nitrogen fraction of cow's milk is hippuric acid.
In connection with the isolation of crystalline biotin from milk in this laboratory, 1 we had occasion to fractionate a biotin concentrate from milk, generously supplied by the S.M.A. Corporation of Chagrin Falls, Ohio. This material had been prepared by charcoal adsorption from a commercial milk residue which remained after the removal of protein and sugar from milk. One gram of the biotin concentrate represented approximately 15 kg of milk.
The first steps in the fractionation of this concentrate for the isolation of biotin included esterification of the concentrate with alcoholic HO and then extraction with ethyl acetate of a slightly alkaline solution of the esterified material. The ethyl acetate extracts were concentrated to remove solvent and the residue TT Table was dissolved in chloroform and chromato-graphed on a column of Decalso. 1
It was found that the chloroform which passed through the columns contained appreciable amounts of a substance which separated in crystalline form when the solutions were concentrated. Recrystallization of this material from an alcohol-ether mixture yielded colorless needles of a nitrogen-containing compound, m.p. 84°, which by alkaline hydrolysis yielded an acid, m.p. 188°. This acid contained 7.7% N and possessed a neutral equivalent of 185. Additional amounts of the free acid were obtained by acidification of the ethyl acetate-extracted esterification residues. These data indicated that the substance isolated from the esterified milk concentrate was the methyl ester of hippuric acid. A mixture of the isolated free acid with hippuric acid showed no depression of the melting point.
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