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The first total synthesis of actinomycins containing L-4-hydroxyproline (1) and the separation and NMR spectroscopic assignment of the regioisomers X Oβ  and iso-X Oβ  (1c, 1e) are described. The synthetic X Oβ  proves, that the oxidized proline ring of the natural actinomycins X Oβ  , X Oδ  and X 2  (1c, 1d, 1b ) is situated in position 3' of the (β)-peptide chain. The new nonnatural variants iso-X Oβ  (1e ) and Bis(hyp)-X 1  (1f) permitted interesting structure/activity studies. Furthermore, the amino acid sequence of the actinomycins X 2  (1b) and X 1a  (1g) could be derived from NMR correlation spectra. A crystal structure analysis confirmed the complete structure of 1b (and thus that of 1c - e ) and showed the characteristical ,,A “-type conformation present in the depsipeptide rings. This corresponds to the solution conformation, which is clearly verified by typical NMR data.

zeitschrift für naturforschung b

Synthese und Struktur von Prolinring-modifizierten Actinomycinen des X-Typs / Synthesis and Structure of Proline Ring Modified Actinomycins of the X-Type