Two simple and efficient synthetic methods for the preparation of semicarbazide amino acid derivatives are reported. The procedures involve reaction between the carbamoyl azides of alpha-N-protected amino acids and hydrazine monohydrate: 4-[(alkoxycarbonylamino)(alkyl)methyl]semicarbazides 1 are obtained when hydrazine is added to the separated tetrahydrofuran (THF) solution containing the carbamoyl azide at 0 °C, whereas 1-[(alkoxycarbonylamino)(alkyl)methylcarbamoyl]-4-[(alkoxycarbonylamino)(alkyl)methyl]semicarbazides 4 are produced by adding hydrazine directly into the final THF/aqueous buffer (KH2PO4) biphasic mixture containing the prepared carbamoyl azide at 50 °C, respectively. NMR experimental data obtained from samples dissolved in [D6]dimethyl sulfoxide suggest a dimeric association for semicarbazides 4 with intermolecular hydrogen bonds. Moreover, the ESI-MS-MS spectra reveal some interesting common features.
