Abstract
The peptide t-butyloxycarbonyl-α-aminoisobutyryl-L-prolyl-L-prolyl-N-methylamide has been shown to adopt an extended structure in the solid state. The Pro-Pro segment occurs in the poly-proline II conformation. On dissolution of single crystals at ∼ 233°K, a single species corresponding to the all trans peptide backbone is observed by 270 MHz 1H NMR. On warming, trans to cis isomerization about the Pro-Pro bond is facilitated. Both cis' (ψ ∼−50°) and trans' (ψ ∼ 130°) rotamers about the Pro 3 C αCO bond are detectable in the Pro-Pro cis conformer, at low temperature. These observations demonstrate unambiguously the large differences in the solid state and solution conformations of a Pro-Pro sequence.
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