ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Cyclic tetradepsipeptides, AM-toxin I and II, are the host-specific phytotoxins of Alternaria mali. In order to elucidate conformation-toxicity relationships, we analyzed the 270-MHz proton nmr spectra of AM-toxins and hydrogenated analogs, (D-Ala2)AM-toxin I (toxic) and (L-Ala2)AM-toxin I (not toxic), in (C2H3)2SO. These cyclic tetradepsipeptides do not contain N-substituted amino acid residues, and all the peptide and ester groups have been found to be transoid. Two conformers with very unequal populations have been found for AM-toxin I and II; the Cβ=Cα—C=O conformations of the Dha2 residues are nonplanar S-trans in the major conformer and nonplanar S-cis in the minor conformer. Only one ring conformation has been found for each of (L-Ala2) and (D-Ala2)AM-toxin I. (L-Ala2)AM-toxin I takes a C4-type ring conformation; all the C=O groups and Cα-H bonds are oriented to the same side of the ring. (D-Ala2)AM-toxin I takes a new ring conformation; the side chain and C=O group of the L-Amp1 residue are oriented to the same side of the ring. This new conformation is also found for the major conformers of AM-toxin I and II and thus appears to be required for the toxicity. The ring conformations of Tyr(OCH3)1-bearing analog tetradepsipeptides have been found to be much the same as those of Amp1-bearing depsipeptides. Furthermore, on the basis of the two distinct conformations of (D-Ala2) and (L-Ala2)AM-toxin I, an empirical rule is proposed for the stable ring conformations of cyclic tetra-D,L-peptides, not containing N-substituted amino acid residues.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360220411
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