1. Preparation of protected peptide amides using the Fmoc chemical protocol. Comparison of resins for solid phase synthesis
S C Story, J V Aldrich Int J Pept Protein Res. 1992 Jan;39(1):87-92. doi: 10.1111/j.1399-3011.1992.tb01560.x.
Different resins were examined for their potential use in the solid phase synthesis of protected peptide amides using the 9-fluorenylmethoxycarbonyl (Fmoc) chemical protocol. The model protected peptide amide BocTyr-Gly-Gly-Phe-Leu-Arg(Pmc)NH2 (1) was synthesized on both the acid-labile 4-(2',4'-dimethoxyphenyl-Fmoc-aminomethyl)phenoxy resin (Rink amide resin) (2) and on resins containing the base-labile linker 4-hydroxymethylbenzoic acid. Of the resins examined only the methylbenzhydrylamine resin containing the 4-hydroxymethylbenzoic acid linkage, which was cleaved by ammonolysis in isopropanol, gave the model peptide 1 in good overall yield (53% including functionalization). Thus the synthesis of protected peptide amides by solid phase synthesis using Fmoc-protected amino acids with t-butyl-type side chain protecting groups is feasible. The choice of peptide-resin linkage and its cleavage conditions, however, are critical to the success of such syntheses. The potential application of this synthetic strategy to the preparation of novel peptide amides is discussed.
2. Solid-phase peptide synthesis at elevated temperatures: a search for and optimized synthesis condition of unsulfated cholecystokinin-12
L M Varanda, M T Miranda J Pept Res. 1997 Aug;50(2):102-8. doi: 10.1111/j.1399-3011.1997.tb01175.x.
A systematic investigation of solid-phase peptide synthesis at elevated temperatures using the well-known aggregating peptide acyl carrier protein (65-74) and the unsulfated cholecystokinin-8 as models is presented. The main goal of the investigation was the determination of an optimized experimental condition for the synthesis of unsulfated cholecystokinin-12. Of the elevated temperatures used, 60 degrees C was the most appropriate. The efficiency of N,N'-diisopropylcarbodiimide/1-hydroxybenzotriazole (DIC/HOBt) in 25% dimethyl sulfoxide (DMSO)/toluene at this temperature was similar to that of 2-(1-H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU). Interestingly, this coupling reagent was more efficient than TBTU, benzotriazol-1-yl oxy-tris(dimethylamino)phosphonium and O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate in N-methylpyrrolidone. 25% DMSO/toluene proved to be suitable for the swelling of the resins phenylacetamidomethyl, methylbenzhydrylamine, hydroxymethylphenoxy, 4-(benzyloxy)-2',4'-dimethoxybenzhydrylamine, 4-(2',4'-dimethoxyphenyl-Fmoc-aminomethyl)phenoxy and (4-succinylamido-2',2',4'-trimethoxy)benzhydrylamine. Those polymeric supports were fully compatible with the approach. Under the optimized synthesis condition found in these studies (temperature of 60 degrees C, DIC/HOBt as coupling reagent and 25% DMSO/toluene as solvent), no difficulties related to the aggregation phenomenon were encountered. These data confirm the usefulness of solid-phase peptide synthesis at elevated temperatures and extend its applicability.
