GENERAL STEPS: Part F. Synthesis of tert-butyl 2(S)-benzyloxycarbonylamino-3-aminopropionate. Dioxane (120 mL) was added to a Parr flask cooled on dry ice, followed by the slow addition of H2SO4 (8 mL). Next, N(α)-Z-L-2,3-diaminopropionic acid (6.88 g, 28.8 mmol) and pre-cooled isobutene (130 mL, excess) were added. The reaction mixture in the Parr vial was shaken at room temperature for 70 hours. Upon completion of the reaction, unreacted isobutene was removed under reduced pressure. The reaction mixture was slowly poured into an ice-water bath cooled NaOH solution (containing 17.4 g NaOH and 400 mL of ether) while stirring vigorously. The ether layer was separated and the aqueous layer was further extracted with ether. All ether layers were combined and washed twice with 1N NaOH solution and subsequently dried with Na2SO4. The dried ether solution was concentrated to give a solid product (6.3 g, 75% yield). The product was characterized by 1H NMR (300 MHz) and mass spectrometry (NH3-Cl): 1H NMR δ 1.44 (s, 9H), 3.10 (m, 2H), 4.26 (m, 1H), 5.12 (s, 2H), 5.80 (d, 1H), 7.36 (m, 5H); MS (NH3-Cl) calculated value (M + 1)+: 293. Measured value: 293.
