Dear Sir. Concerning your issue about the glutamic acid protection using cbz. A simple and efficient protection procedure is general and regioselective for the preparation of mono-N-Boc, N-Cbz, N-Fmoc or N-Alloc aromatic amines in high yield without affecting aliphatic amino groups and other functionalities (V. Perron, S. Abbott, N. Moreau, D. Lee, C. Penney, B. Zacharie, Synthesis, 2009, 283-289). I think the following below links may help you in your analysis:
Common Cbz protection method for the amine is to use Cbz-Cl, Na2CO3 or NaOH in water and/or THF at 0oC and warm to room temperature. Cbz chloride is very toxic and pungent and should only be used in a ventilated fumehood.