I have tried with EDCI, DCC, those are not working properly. Can you suggest me mild reaction conditions? Acetyl groups and pincolone group deprotected conditions are also not a problem.
May be you can try EEDQ reagent in DMF. The mecanism is defferent. You pass by an anhydride and sometimes, on complicated structures, it could be a good option.
Convert the amino acid to the methyl ester if possible and then treat with large excess of hydrazine hydrate (12 eq of the amino acid) in ethanol and reflux for an hour. Monitor using TLC. Reference: Synlett, 2007(7):1083-1084