A solution of 29, N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide (244 mg, 0.59 mmol) in 1,4-dioxane (1.0 mL) was placed under an atmosphere of N2.