Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Terminally blocked, isotactic homopeptides from the sterically demanding α-methylvaline of general formula Y-[L-(αMe)Val]n-OtBu (Y = Z, pBrBz, Ac; n = 2-8) have been prepared step-by-step in solution and fully characterized. The conformations preferred in solution (β-turn and right-handed 310-helix) have been assessed by FT-IR, 1H NMR and CD spectroscopy. The molecular and crystal structures of the Z-protected trimer, hexamer, heptamer and octamer have been determined by X-ray diffraction. In the crystal state, while the trimer is folded in a type III β-turn conformation, the longest homopeptides form well-developed, regular, right-handed 310-helices. The screw sense in the helix of the pBrBz-blocked octamer has been confirmed to be right-handed by solid-state and solution CD spectroscopy. The possible exploitation of these peptide helices as rigid and precise molecular rulers is discussed.
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