Quantitative protein sequencing using mass spectrometry: Mass spectral analysis of 2-anilino-5-thiazolinone derivatives of amino acids without prior conversion to the phenyl thiohydantoins

The use of mass spectrometry to directly analyze for the 2-anilino-5-thiazolinone amino acid derivatives from the Edman reaction has been described. A comparison of the mass spectra of a number of thiazolinone derivatives with those of the corresponding phenyl thiohydantoin derivatives has been made and a close similarity between the two sets of spectra is observed. This similarity in mass spectral behavior is interpreted as evidence that the thiazolinone derivatives undergo thermal rearrangement to the more stable thiohydantoin structure during mass spectral analysis. The ability to analyze the thiazolinone derivative directly by mass spectrometry is discussed and further demonstrated by using the method to identify the products of the N-terminal Edman degradation of Ribonuclease.