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Fig. 2. Side-chain region of the TOCSY spectrum of the left-handed tetrapeptide Z-L-Hyp-D-Iva-L-Iva-Gly-OtBu in CDCl 3 solution.The opposite behavior is observed for the left-handed, synthetic, intermediate Z-Aib-L-Hyp-L-Iva 14 -D-Iva 15 -OtBu (Z, benzyloxycarbonyl; OtBu, tert-butoxy) (Figure 2). Here, theγ-methyl protons of L-Iva 14 are more shielded (0.838 ppm) than those of D-Iva 15 (0.905ppm).The chemical shift difference between the diastereotopic β-methylene protons of theIva side chains in the right-handed helical peptides is much larger for D-Iva than for L-Iva.For D-Iva 14/15 , the values range from 0.38 to 0.63 ppm, whereas for D-Iva 1 the value isbetween 0.26 and 0.31 ppm. In each case, the difference is always larger for the D-Iva thanfor the L-Iva residues (which is always ≤ 0.19 ppm). Again, an opposite behavior is seen forthe left-handed tetrapeptide.Overall, our method enables the non-destructive assignment of the configuration ofeach Iva residue in peptides of known helical screw sense.References1. Toniolo, C., Brückner, H. (Eds.) Peptaibiotics: Fungal Peptides Containing α-Dialkyl α-AminoAcids, Verlag Helvetica Chimica Acta, Zürich, Switzerland and Wiley-VCH, Weinheim, Germany,2009.2. De Zotti, M., Damato, F., Formaggio, F., Crisma, M., Schievano, E., Mammi, S., Kaptein, B.,Broxterman, Q.B., Felock, P.J., Hazuda, D.J., Singh, S.B., Kirschbaum, J., Brückner, H., Toniolo,C. Chem. Eur. J. 16, 316-327 (2010).3. Degenkolb, T., Brückner, H. Chem. Biodivers. 5, 1817-1843 (2008).543