Fmoc-Asp-allyl ester

α-Allyl esters are useful tools for the on-resin head-to-tail cyclization of peptides and for the synthesis of side-chain lactam peptides, glyco- and sulfo-peptides, and branched peptides. Allyl esters are cleaved under mild conditions using Pd(0). These conditions are compatible with Fmoc- and Boc-SPPS. The Asp α-Allyl esters show a somewhat higher propensity for base-catalyzed aspartimide formation than the corresponding β-esters. Fmoc-Asp-OAll is a versatile educt for synthesizing complex Asp and Asn derivatives, e.g., N-glycosylated Asn building blocks.