Identification of pyrroloindoline-containing cyclic hexapeptides in the metabolites of Streptomyces alboflavus 313 by HPLC-DAD-ESI-MS/MS

Abstract

To investigate the chemical biodiversity of biologically active cyclic hexapeptides in the metabolites from microorganisms, the fermentation broth of Streptomyces alboflavus 313 was analyzed using HPLC, equipped with a diode array detector (DAD), coupled with ESI tandem MS (HPLC-DAD-ESI-MS/MS). In the mass spectra of cyclic hexapeptides, predominant ions [M+H](+), as well as [M-18+H](+), [M-28+H](+) and [M+Na](+), were observed and used to determine the molecular masses, while fragmentation reactions of [M+H](+) were recorded to provide information on the contents of amino acids and their linkage sequence. Based on the fragmentation patterns and comparison with standards, 15 pyrroloindoline-containing natural cyclic hexapeptides, cp01-15, were identified from the microorganism and six of these are reported for the first time.

Enzymatic Halogenation and Dehalogenation Reactions: Pervasive and Mechanistically Diverse

“…Whether the 1,2-epoxidation of the indole ring, followed by cyclization via the main chain nitrogen atom to generate the tricyclic pyrroloindoline motif occurs post or prior to incorporation in the NRPS peptide remains to be discerned. Chlorinated pyrroloindolines, postulated to be synthesized by as yet unidentified FDHs, also occur in the NRPS-derived chloptosin ( 39 ) and other structurally related peptides isolated from Streptomyces alboflavus 313 (Figure C) . Similarly, while the above-mentioned hypotheses for the action of the FDHs Tar14, KtzQ, and KtzR have not been experimentally verified, adenylation domains that recognize and activate halogenated precursors in NRPS assembly lines are attractive “plug-and-play” elements that can be used to regiospecifically engineer natural product scaffolds to bear halogens, a modification that is likely challenging to be affected using chemical derivatization techniques.…”

Synthesis of 3a‐hydroxyhexahydropyrrolo[2,3‐B]Indole‐2‐carboxamide, an oxidation product of tryptophan present in natural products

“…Not all HO‐HPIC‐bearing toxins contain diketopiperazine scaffolds. For example, two structurally related cyclic peptides and cyclic depsipeptides containing an HO‐HPIC and piperazic acid are himastatin ( 13 ) and chloptosin ( 14 ), both of which were isolated from Streptomyces strains (Figure ) . Chloptosin ( 14 ) contains exclusively nonproteinogenic amino acids including piperazic acid residues and a 6‐chloro‐HO‐HPIC moiety.…”

“…Pseudo‐monomers of himastatin ( 13 ) and chloptosin ( 14 ) were also identified in fungi. For example, the NW‐G family was isolated from Streptomyces alboflavus 313 . The NW‐G family encompasses at least nine members.…”