Once the octadeca-(glyco)peptides were prepared, we focused on the removal of the two acid-stable protecting groups, namely neopentyl (Np) at the 2-Tyr(SO3Np) and acetyl groups at the 16-Hyp[(2,3,5-OAc)Ara]0-3 . For the non-arabinosylated control peptide PSY1 16-Hyp 20 only Np removal in 2M ammonium acetate solution fulfills the complete synthesis of this peptide resulting in Brassica PSY1 16-Hyp 1. However, for glycopeptides 21-23 the order of deprotection was found important to maintain pure PSY1 peptide in complete sequence. Specifically, starting with Np removal from acetylated glycopeptide 21 using a 2M ammonium acetate solution resulted in multiple peaks in liquid chromatography trace (Figure ). Subsequent deacetylation did not provide the correct mass of the desired glycopeptide. Fortunately, deacetylation using sodium methoxide in methanol, followed by lyophilization to obtain glycopeptides 24-26, and subsequent removal of the tyrosine sulfate Np protecting group with 2M ammonium acetate afforded the desired PSY1 peptides 16-Ara1Hyp 2, 16-Ara2Hyp 3, and 16-Ara3Hyp 4 in high purity after lyophilization. ii