1-(4,4-Dimethyl-2,6-dioxocyclohex- 1-ylidene)ethyl (Dde), an amino-protecting group cleavad by 2% hydrazine hydrate in DMF. Nω-Dde can be selectively removed after Fmoc-SPPS from Dap, Dab Orn, or Lys allowing on-resin modification of the Nω-amino group.

See also ivDde and Dmab.