The dimethyl ester product from part (e) (1.04 g., 1.81 mmole) is dissolved in dichloromethane (10 ml.) and treated with trimethysilylbromide (0.52 ml., 605 mg., 3.96 mmole). The mixture is stirred under argon overnight then concentrated in vacuo. Dioxane (15 ml.) and water (5 ml.) are added and the resulting mixture is stirred for 15 minutes and then concentrated. Residual water is chased three times with acetonitrile (20 ml.) giving 1.06 g. of [1-[[N2 -(cyclobutylcarbonyl)-N6 -[(phenylmethoxy)carbonyl]-L-lysyl]-2-phenylethyl]phosphonic acid as an organe-yellow foam. TLC (silica gel; isopropanol:ammonia:water, 7:2:1) Rf =0.42.
