Fmoc-Asp(OtBu)-OH- 13 C 4 , 15 N is the 13 C and 15 N labeled Fmoc-Asp(OtBu)-OH. Fmoc-Asp(OtBu)-OH (4-tert-Butyl N-(fluoren-9-ylmethoxycarbonyl)-L-aspartate) is a aspartate derivative containing amine protecting group Fmoc. Fmoc-Asp(OtBu)-OH can be used for peptide synthesis.