L-Cysteine,S-(1,1-dimethylethyl)-N-[O-(1,1-dimethylethyl)-N-[O-(1,1-dimethylethyl)-N-[N-[O-(1,1-dimethylethyl)-L-threonyl]-L-phenylalanyl]-L-threonyl]-L-seryl]-, 1,1-dimethylethyl ester