Aspartimide formation of the highly base-labile Asp-Gly motif during Fmoc-SPPS may be completely suppressed by coupling this Hmb-protected dipeptide derivative. Additionally, Hmb prevents aggregation of the growing peptide chain as efficiently as the incorporation of a pseudoproline moiety. O-Acylation renders the Hmb moiety acid-stable facilitating the purification of peptides prone to form aggregates. The acyl group can be removed with hydrazine hydrate in DMF (cf. Quibell).