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Unusual Equilibrium between η1- and η2-Isomers of Selenobenzaldehyde Complexes

✍ Scribed by Priv.-Doz. Dr. Helmut Fischer; Dr. Siegfried Zeuner; Jürgen Riede

Publisher
John Wiley and Sons
Year
1984
Tongue
English
Weight
249 KB
Volume
23
Category
Article
ISSN
0044-8249

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✦ Synopsis

the ring (17)[71. These compounds were also no& identical with Dolastatin 3. The following characteristic differences in the NMR spectra of the 16 diastereomers and that of Dolastatin 3 were found: 1) Different chemical shift and coupling for the amide protons, 2) different chemical shift and coupling for the two methylene protons in the 2-position of a thiazole moiety, 3) consistently greater difference in the chemical shift of the two 5-thiazole protons, and 4) different chemical shift for all the methyl protons.

The structure proposed for Dolastatin 3 is therefore not correct. The scheme described for the synthesis of 16 isomers with the structures 16 and 17 in good yields may be used for the economic synthesis of other isomers with different amino acid sequences.

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