Amino acid-N-carboxy anhydrides having an N-acyl substituent at nitrogen which are represented by the following general formula (1); and a process for producing the same. These compounds easily react with free amino acids, alcohols or nucleophilic agents such as anions and serve as useful intermediates in producing amino acid derivatives, optically active compounds, peptides, polypeptides and the like, which are useful in various fields including medicines and pesticides, at a high yield. Moreover, a process for producing diamides by using the compounds of the formula (1) with amine derivatives represented by the following general formula (7). These diamides are also appropriately usable in producing amino acid derivatives, optically active compounds, peptides, polypeptides and the like. |