A Simple and Convenient Synthesis of ω-tert-Butyl Esters of Fmoc-Aspartic and Fmoc-Glutamic Acids
17. September 2002 (online)
N-(9-Fluorenylmethoxycarbonyl)aspartic acid β-tert-butyl ester (3b) [Fmoc-Asp(OBu-t)] and N-(9-fluorenylmethoxycarbonyl)-glutamic acid γ-tert -butyl ester (4b) [Fmoc-Glu(OBu-t)] were prepared from aspartic and glutamic acids by treatment with isobutene and 4-toluenesulfonic acid followed by Fmocsuccinimide in a novel two-step, one-pot procedure to give the title compounds in moderate yield. The major byproduct of the reaction is the corresponding α-tert-butyl ester, which can be easily separated and purified.