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Two Novel Hexadepsipeptides with Several Modified Amino Acid Residues Isolated from the Fungus Isaria

Gudihal, Ravindra and Rappal, Ranganayaki S and Raghothama, Srinivasa and Mandayam, Srinivasan C and Gilardi, Richard D and Karle, Isabella L and Balaram, Padmanabhan (2004) Two Novel Hexadepsipeptides with Several Modified Amino Acid Residues Isolated from the Fungus Isaria. In: Chemistry & Biodiversity, 1 (3). pp. 489-504.

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Abstract

Two new cyclohexadepsipeptides have been isolated from the fungus Isaria. Fungal growth in solid media yielded hyphal strands from which peptide fractions were readily isolable by organic-solvent extraction. Two novel cyclodepsipeptides, isaridin A and isaridin B, have been isolated by reverse-phase HPLC, and characterized by ESI-MS and 1H-NMR. Single crystals of both peptides have been obtained, and their 3D structures were elucidated by X-ray diffraction. The isaridins contain several unusual amino acid residues. The sequences are cyclo( -Gly-HyLeu-Pro-Phe-NMeVal-NMePhe) and cyclo( -Gly-HyLeu- -MePro-Phe-NMeVal-NMePhe), where NMeVal is N-methylvaline, NMePhe N-methylphenylalanine, and HyLeu hydroxyleucine (=2-hydroxy-4-methylpentanoic acid). The two peptides differ from one another at residue 3, isaridin A having an (S)-proline at this position, while -methyl-(S)-proline (=(2S,3S)-2,3,4,5-tetrahydro-3-methyl-1H-pyrrole-2-carboxylic acid) is found in isaridin B. The solid-state conformations of both cyclic depsipeptides are characterized by the presence of two cis peptide bonds at HyLeu(2)-Pro(3)/HyLeu(2)- -MePro(3) and NMeVal(5)-NMePhe(6), respectively. In isaridin A, a strong intramolecular H-bond is observed between Phe(4)CO HN -Gly(1), and a similar, but weaker, interaction is observed between -Gly(1)CO HNPhe(4). In contrast, in isaridin B, only a single intramolecular H-bond is observed between -Gly(1)CO HNPhe(4).

Item Type: Journal Article
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Additional Information: Copyright of this article belongs to Verlag Helvetica Chimica Acta AG, Zürich
Keywords: cyclohexadepsipeptides;fungus;isaria;hydrogen bond
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Chemical Sciences > Sophisticated Instruments Facility
Date Deposited: 08 Jun 2004
Last Modified: 30 Jan 2014 12:28
URI: http://eprints.iisc.ernet.in/id/eprint/330

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