Solid phase synthesis and selected NMR studies of peptides

Peptides corresponding to the sequences Pro-Tyr-Ser, Asp-Pro-Tyr-Arg, Asp-Pro-Tyr-Ser, and Glu-Tyr-Pro-Thr were synthesized by the standard solid phase method. Yields obtained were in the range of 20%. HF dried over CoF[lowered 3] was used to cleave the peptide from the resin. Co[raised III] contamination during one synthesis of Asp-Pro-Tyr-Arg, warranted purification. Attempts to separate Co[raised III] by EDTA lead to hydrolysis of the peptides, producing Tyr-Arg in very low yields. The pure peptide Asp-Pro-Tyr-Arg was obtained later by cleaving the peptide from the resin with HF not dried over CoF[lowered 3]. All peptides synthesized were first deuterated and then studied by PMR at 100MHz. Peaks were assigned with the help of previously published data(l,2). Fully protonated peptide, Glu-Tyr-Pro-Thr in DMSO revealed an extremely complex PMR spectrum at variable temperatures, but does indicate some form of intramolecular hydrogen bonding. This could be due to the absence of any hindrance for the peptide to form a reverse turn and also due to 1-) 4 hydrogen bond stabilizing interaction. Preliminary [raised 1]H & [raised 13]C spectra of the peptide Glu-Tyr-Pro-Thr indicated the possibility of two different conformational states for the peptides, but further work has to be done before any conclusive statements can be made. Such work is underway in our laboratory.