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Sigma Aldrich, Trifluoroborate (DIPEA)

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All reagents were of the highest quality available and were purchased either from Sigma Aldrich, Merck, Fluka, Scharlau Chemie, Roth, CALEDON, Gibco, Invitrogen or Biofil. N,N,N',N'-Tetramethyl-O-(benzotriazol-l-yl)Uronium Tetrafluoroborate (TBTU), Triisopropylsilane (TIS), 1-hydroxybenztriazole (HOBt), 5(6) Carboxyfluorescein (FAM), Potassium cyanide, Methotrexate and Ninhydrine were obtained from Sigma-Aldrich (St. Louis, MO, USA). 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) was from Roth (Karlsruhe, Germany). Piperidine was obtained from BDH Laboratory Supplies (England). Trifluoroacetic acid (TFA) was from Fluka (Buchs, Switzerland). N-ethyldiisopropylamine (DIPEA), Triethylamine (TEA), Dimethyl Sulfoxide (DMSO), Acetonitrile…show more content…
The Fmoc protected amino acids with different side chain protecting groups were used as the following derivatives: Fmoc-Arg(Pbf)-OH, Fmoc-Trp(Boc)-OH, Fmoc-Lys(Boc)-OH, Fmoc-Gly-OH, Fmoc-Gln(Trt)-OH and…show more content…
The resin was swollen in dry DCM (approximately 10 ml per gram of resin) for 1.5 h under dry nitrogen. After removal of the DCM, the first Fmoc-protected amino acid coupling was carried out by addition of 5.0 equivalents DIPEA as activating reagent to 2.0 equivalents amino acid in DCM/DMF mixture (3:1). The first amino acid was loaded on the resin at the C-terminal with the loading efficiency about 1.08 mmol.g−1 and the reaction vessel was stirred for 3 hours. The resin was end-capped by adding 0.8 ml of MeOH for 1 g of resin (0.2 ml for 250 mg), then washed with DCM (2*3 ml) and DMF (2*3 ml). The Fmoc protecting group was removed with 2 ml of 20-40% (v/v) Piperidine/anhydrous DMF solution for about 1 h. The resin was then washed with DCM (2*3 ml) and DMF (2*3 ml), respectively. The effectiveness of the deprotection was monitored by testing for free amine groups with the Ninhydrine Test. In the next step, 2.0 equivalents of the Fmoc-protected amino acid and 5.0 equivalents of TBTU as coupling reagent with 5.0 equivalents of HOBt in 10 ml of DMF were added to the resin. 5.0 equivalents of DIPEA were added and the reaction vessel was stirred for about 3 hours at room temperature as the first coupling. After loading the first amino acid, the desired peptide sequence
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