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Eur. J. Mass Spectrom. DOI: 10.1255/ejms.531

Profiling of cyclic hexadepsipeptides roseotoxins synthesized in vitro and in vivo: a combined tandem mass spectrometry and quantum chemical study

Alexandr Jegorov
IVAX Pharmaceuticals a.s., Branislovská 31, 370 05 Ceské Budejovice, Czech Republic
Béla Paizs
Martin Zabka
University of Southern Bohemia, Faculty of Agriculture, Stendská 13, CZ-370 05 Ceské Budejovice, Czech Republic
Marek Kuzma and Vladimír Havlícek*
Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídenská 1083, CZ-142 20 Prague 4, Czech Republic
Anastassios E. Giannakopulos and Peter J. Derrick
University of Warwick, Department of Chemistry, Gibbet Hill Road, Coventry CV4 7AL, UK

ABSTRACT:
High-performance liquid chromatography and tandem mass spectrometry (HPLC/MS/MS) was used for the detection of cyclic hexadepsipeptides roseotoxins produced by Trichothecium roseum. Roseotoxins were found both in submerged standard cultivation on Czapek-Dox medium, as well as in vivo cultivation extract obtained from an apple. Roseotoxin chromatographic profiles from these two experiments were compared. Product ion collision-induced dissociation (CID) spectra obtained on an ion trap (electrospray ionisation, ESI) were used for the identification of natural roseotoxins A, B, C and of minor destruxins A and B. Dissociation behaviour of roseotoxins is discussed in terms of a fragmentation scheme proposed for describing dissociation pathways of cyclic peptides. This scheme involves opening of the cyclopeptide ring via formation of oxazolone derivatives and fragmentation of the resulting linear species which have a free N- and an oxazolone ring at the C-terminus, respectively. Some aspects of this fragmentation scheme are underlined by modelling the dissociation channels of Roseotoxin A using quantum chemical calculations. The structures of roseotoxin A and destruxin B were verified by nuclear magnetic resonance (NMR) spectroscopy. Structures of three new minor natural roseotoxins [Val4]RosA, [MeLxx4]RosA and [MeLxx4]RosB were deduced by Fourier transform mass spectrometry (FT-MS) and ion trap tandem mass spectrometry by examining the pre-separated roseotoxin fraction.

Keywords:

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