Cyclic peptides. XVI. Syntheses of AM-toxin I analogs containing a lower or higher homolog of the component L-2-amino-5-(p-methoxyphenyl)pentanoic acid residue.

In order to investigate the influence of the side-chain length at position 3 of AM-toxin I (cyclic tetradepsipeptide) on necrotic activity for apple leaf, two analogs of AM-toxin I, [L-2-amino-4-(p-methoxyphenyl)butanoic acid]-AM-toxin I and [L-2-amino-6-(p-methoxyphenyl)hexanoic acid]-AM-toxin I, were synthesized by the conventional method. Spectra of 1H-n.m.r., u.v. and CD of the analogs were similar to those of natural or synthetic AM-toxin I. The toxic activities of the analogs for apple leaf, however, were weak, indicating that the exact side-chain length at position 3 must be one of the important factors for the induction of the activity. The interaction between AM-toxin I and a possible receptor on apple leaf is discussed.