The Structure of Acetone-Oxytocin with Studies on the Reaction of Acetone with Various Peptides

The structure of acetone-oxytocin has been shown to possess a 2,2-dimethyl-4-imidazolidinone ring structure in which the isopropylidene group from acetone forms a bridge between the nitrogen of the free amino group of oneof the half-cystine residues of oxytocin and the nitrogen of the peptide bond between this half-cystine residue and the succeeding tyrosine residue. These results were obtained by extensive comparison of the chemical and spectral properties of the acetone derivative of S-benzyl-L-cysteinyl-L-tyrosine, from which acetone-oxytocin can be synthesized, with those of 2,2-dimethyl-4-imidazolidinone and 5-imino-2,2-dimethyloxazolidine. When L-prolyl-L-leucylglycinamide was treated with acetone under anhydrous conditions, a product was isolated which similarly was shown to be a substituted 2,2-dimethyl-4-imidazolidinone. On the other hand, treatment of S-benzyl-L-cysteinyl-L-prolyl-L-leucylglycinamide which can form neither an imidazolidinone nor an oxazolidine with acetone afforded no isolable product. However, the rapid formation of a Schiff base could be demonstrated by a trapping experiment using sodium borohydride which led to the formation of N-isopropyl-S-benzyl-L-cysteinyl-L-prolyl-L-leucyl-glycinamide.