The peptides were prepared using 9-fluorenylmethyloxycarbonyl (Fmoc) solid-phase synthesis as described previously.45 (link) Briefly, the Fmoc group of H-Rink Amide ChemMatrix resin (0.47 mmol/g) (PCAS BioMatrix) was cleaved with a solution of 6% (wt %) piperidine and 1% (wt %) 1-hydroxybenzotriazole monohydrate (HOBt) in dimethylformamide (DMF) for 20 min and subsequently washed with methanol (MeOH) and dichloromethane (DCM). A coupling solution of Fmoc-protected amino acid (4.0 equiv), tetramethyl-O-(1H-benzotriazol-1-yl) uranium hexafluorophosphate (HBTU) (3.9 equiv), and N,N-diisopropylethylamine (DIEA) (8.0 equiv) was prepared in DMF and incubated with the resin for 90 min. After being washed with MeOH and DCM, the successive Fmoc protecting groups were removed using the same deprotection and washing steps used for the resin, and the progress of the synthesis was periodically verified by electrospray ionization (ESI) mass spectrometry (SCIEX 3200 QTRAP, SCIEX, Framingham, MA). At the end of the solid-phase synthesis, the N-terminal amino acid was acetylated with a solution of acetic anhydride and DIEA in DMF. The peptide was then cleaved from the resin with a solution of 2.5% (vol %) triisopropylsilane and 2.5% (vol %) water in trifluoroacetic acid (TFA) for 2 h and precipitated with cold diethyl ether.