title: Identification and characterization of a library of microheterogeneous cyclohexadepsipeptides from the fungus Isaria.
abstract: Ten new cyclic hexadepsipeptides, six isariins and four isaridins, from the fungus Isaria have been identified and characterized by high-performance liquid chromatography, coupled to tandem electrospray ionization mass spectrometry (LC-ESIMS/MS). The isariins possess a beta-hydroxy acid residue and five alpha-amino acids, while isaridins contain a beta-amino acid, an alpha-hydroxy acid, and four alpha-amino acids. One- and two-dimensional NMR spectroscopy confirmed the chemical identity of some of the isariin fractions. Mass spectral fragmentation patterns of [M + H]+ ions reveal clear diagnostic fragment ions for the isariins and isaridins. Previously described cyclic depsipeptides, isarfelins from Isaria felina (Guo, Y. X.; Liu, Q. H.; Ng, T. B.; Wang H. X. Peptides 2005, 26, 2384), are now reassigned as members of the isaridin family. Examination of isaridin sequences revealed significant similarities with cyclic hexadepsipeptides such as destruxins and roseotoxins. The structure of an isariin (isariin A) investigated by NMR spectroscopy indicated the presence of a hybrid alphabeta C11 turn, formed by the beta-hydroxy acid and glycine residues and a D Leu-L Ala type II' beta-turn. Additionally, the inhibitory effect of isariins and an isaridin on the intra-erythrocytic growth of Plasmodium falciparum is presented.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India.
authors.forename: V
authors.initials: V
authors.lastname: Sabareesh
authors.forename: R S
authors.initials: RS
authors.lastname: Ranganayaki
authors.forename: S
authors.initials: S
authors.lastname: Raghothama
authors.forename: M P
authors.initials: MP
authors.lastname: Bopanna
authors.forename: Hemalatha
authors.initials: H
authors.lastname: Balaram
authors.forename: M C
authors.initials: MC
authors.lastname: Srinivasan
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000962:Antimalarials / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D047630:Depsipeptides / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D003904:Mitosporic Fungi / Q000737:chemistry*; D015394:Molecular Structure; D010963:Plasmodium falciparum / Q000187:drug effects*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D000962:Antimalarials; D047630:Depsipeptides