Experimental Methods Materials The following materials were used in the preparative examples: Fmoc-Phe-Wang resin (100-200 mesh, 0.66 mmol g -1 substitution), Fmoc-D-Phe-Wang resin (100-200 mesh, 0.66 mmol g -1 substitution), Fmoc-Phe-OH, Fmoc-D-Phe-OH, Fmoc-Val-OH, Fmoc-D-Val-OH, Fmoc-Leu-OH, Fmoc-D-Leu-OH, Fmoc-Lys(Boc)-OH, Fmoc-D-Lys(Boc)-OH, Fmoc-β-Ala-OH, and Fmoc-γ-Abu-OH (Fmoc-GABA) were purchased from Novabiochem (UK). (R)-Fmoc-4-amino-6-methyl-heptanoic acid,

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... entanoic acid and (R)-Fmoc-4-amino-5-(4-tertbutoxyphenyl)-pentanoic acid were purchased from PolyPeptide Laboratories France SAS. Trifluoroacetic acid (TFA), piperidine and triisopropylsilane (TIPS) were purchased from Sigma-Aldrich. HOBt/DMF (a mixture of 1-hydroxybenzotriazole and dimethylformamide), DIPEA/NMP (a mixture of diisopropylethylamine and Nmethylpyrrolidone), and NMP were obtained from Applied Biosystems(UK). Water (HPLC grade), acetonitrile (HPLC grade), dimethylformamide (DMF), methanol (MeOH) and dichloromethane (DCM) and diethyl ether were purchased from Fisher Scientific (UK). General Synthesis Methods The peptides shown in Scheme 1 were synthesized by solid phase methods using standard FastMoc chemistry [Fmoc (9-fluorenylmethyloxycarbonyl) protecting group and activation by HBTU/HOBt]. A 0.25 mmol scale synthesis was conducted with a fully automated peptide synthesizer (433A Applied Biosystems), which allowed for direct conductivity monitoring of Fmoc deprotection. Alternatively, a batchwise synthesis (> 0.50 mmol scale) was carried out using a fritted reaction glass vessel Electronic Supplementary Material (ESI) for Chemical Communications This journal is