α-Azido Acids in Solid-Phase Peptide Synthesis: Compatibility with Fmoc Chemistry and an Alternative Approach to the Solid Phase Synthesis of Daptomycin Analogs

α-Azido acids have been used in solid phase peptide synthesis (SPPS) for almost 20 years. Here we report that peptides bearing an N-terminal α-azidoaspartate residue undergo elimination of an azide ion when treated with reagents that are commonly used for removing the Fmoc group during SPPS. We also report an alternative solid-phase route to the synthesis of an analog of daptomycin that uses a reduced number of α-azido amino acids and without elimination of an azide ion.