title: Two novel hexadepsipeptides with several modified amino acid residues isolated from the fungus Isaria.
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(beta-Gly-HyLeu-Pro-Phe-NMeVal-NMePhe) and cyclo(beta-Gly-HyLeu-beta-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 beta-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)-beta-MePro(3) and NMeVal(5)-NMePhe(6), respectively. In isaridin A, a strong intramolecular H-bond is observed between Phe(4)CO...HNbeta-Gly(1), and a similar, but weaker, interaction is observed between beta-Gly(1)CO...HNPhe(4). In contrast, in isaridin B, only a single intramolecular H-bond is observed between beta-Gly(1)CO...HNPhe(4).
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore-560012, India.
authors.forename: Gudihal
authors.initials: G
authors.lastname: Ravindra
authors.forename: Rappal S
authors.initials: RS
authors.lastname: Ranganayaki
authors.forename: Srinivasa
authors.initials: S
authors.lastname: Raghothama
authors.forename: Mandayam C
authors.initials: MC
authors.lastname: Srinivasan
authors.forename: Richard D
authors.initials: RD
authors.lastname: Gilardi
authors.forename: Isabella L
authors.initials: IL
authors.lastname: Karle
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000235:genetics / Q000302:isolation & purification*; D000818:Animals; D047630:Depsipeptides / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D003904:Mitosporic Fungi / Q000235:genetics / Q000302:isolation & purification*; D051381:Rats
chemical_list: D000596:Amino Acids; D047630:Depsipeptides; D005656:Fungal Proteins