Fmoc-Ala-OPfp

The pentapeptide sequences were assembled on a Fmoc-Val-Pepsyn-KA-resin (0.08 mequiv-g 1) using a Biolynx synthesizer. Fmoc(Fmoc-Hmb)N-Gly-OH was incorporated using its pentafluorophenyl ester with HOBt catalysis for 45 min. Fmoc-Ala-OPfp was double coupled to the terminal (Hmb)tripeptide-resin for 2 h. All couplings not involving an Hmb-substituted residue were performed using standard 0.5 mmol scale coupling protocols. 

Fig. 2. Dependency of spot size on the manually delivered volume of Fmoc-(3-Ala-OPfp/DMSO solution on Whatman 50 filter paper.

The assembly was repeated using (Hmb)Ala , coupled via 3 eq Fmoc-A -(FmocHmb)Ala-OPfp/HOBt onto H-Thr( Bu) —PEG-PS in 4 h. This was followed by 10 eq FmocArg(Pmc) )20 (prepared via Protocol 4 in DCM) for 12 h. No synthetic difficulties were observed during the remainder of the assembly and a substantially improved quality of product was obtained (Figure 6b). 

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