The Nde (1-(4-Nitro-1,3-dioxo-indan-2-ylidene)ethyl) protecting group, which is selective for primary amines, is orthogonal to both Fmoc and Boc protection and therefore useful to enable extension from lysine side chains by using Fmoc-Boc solid-phase methodologies. Nde can be cleaved by 2% hydrazine in DMF at ambient temperature.