Gas Chromatography–Mass Spectrometry of Trimethylsilylated Imino Derivatives of Alanine

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Abstract
Trimethylsilylation of seven imino derivatives of alanine with N,O-bis(trimethylsilyl)trifluoroacetamide in acetonitrile was studied. The imino derivatives include 2,2′-iminodipropionitrile (1), 2,2′-iminodipropionamide (2), 2,2′-iminodipropionic acid (3), 2-(1-cyanoethylamino)propionamide (4), 2-(1-cyanoethylamino)propionic acid (5), 2-(1-carbamoylethylamino)propionic acid (6), and 3,5-dimethyl-2,6-piperazinedione (7). The reaction products were identified by gas chromatography–mass spectrometry. Under the present reaction conditions (at 100 °C for 30 min), hydrogen atoms of carboxyl and carbamoyl groups and an imide hydrogen were readily replaced by the trimethylsilyl (TMS) group, but imino hydrogens were not replaced because of the steric hindrance of N-substituent group. For the carbamoyl group, only one hydrogen was replaced. Consequently, 1 was not trimethylsilylated. Furthermore, no definite trimethylsilylation products were obtained for 4. Upon electron impact at 70 eV, 2, 3, and 5–7 gave rather simple spectra with molecular (M+) and M −15 (loss of CH3) ions characteristic of TMS derivatives. A fragment, M −117 (loss of COOTMS) or M −116 (loss of CONHTMS), was very prominent for 2, 3, 5, and 6. Other important ions such as m/z 70 were noted. Preparations and properties of some of the imino derivatives are also described.