Isariins B, C and D, isolated from a strain of Isaria felina, were shown to be cyclodepsipeptides constituted by a pentapeptide cyclized through a b-hydroxyacid.The nature of the latter and the sequence of the peptide were determined for each compound.Relations between insecticidal activity and structure of the depsipeptides were pointed out.We reported in the precedent paper1) the isolation of four compounds (I -IV) from synnemata of the imperfect fungus Isaria felina (=I. cretacea), two of which exhibited insecticidal properties against Galleria mellonella larvae.We now bring evidences of their cyclodepsipeptidic structure, and of identity of compound I with the previously described isariin. ResultsUV spectra of the four compounds showed end absorption. Their IR spectra were very similar.Several intense bands between 2850 and 2970 cm-1 were in favour of an aliphatic component. A broad band between 3030 and 3300 cm-1 (NH) and two bands at 1640 and 1540 cm-1 (CO of a secondary amide group) were characteristic of peptidic bonds. An absorption at 1740 cm-1 could be assigned to the CO of an ester group. All these data, which were similar to those obtained by VINING and TABER with isariin2), were consistent with a cyclodepsipeptidic structure.Molecular mass and empirical formula of each compound were determined by high resolution mass spectrometry and were in agreement with elementary analysis. These results, and its melting point, showed that I was presumably identical with isariin, and that the other three compounds were closely related to it. This was confirmed by the study of the peptide and hydroxyacid of all four compounds.Vigorous acid hydrolysis yielded the sane four amino acids: glycine, alanine, valine and leucine.The latter was shown to be of the D-configuration, as in isariin, whereas alanine and valine were of the L-. Quantitative analysis of the hydrolysates showed that the amino acids constituted a pentapeptide with the same composition in I and II on the one hand, III and IV on the other hand.t To whom correspondence should be addressed.

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