Following the procedure described for the preparation of tert-butyl [(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]carbamate but substituting Boc-(β t-butyl)-Ala-OH and making noncritical variations provided a brown syrup.