Tricholides A and B and Unnarmicin D: New Hybrid PKS-NRPS Macrocycles Isolated from an Environmental Collection of Trichodesmium thiebautii

Abstract

Bioassay-guided isolation of the lipophilic extract of Trichodesmium thiebautii bloom material led to the purification and structure characterization of two new hybrid polyketide-non-ribosomal peptide (PKS-NRPS) macrocyclic compounds, tricholides A and B (1 and 2). A third macrocyclic compound, unnarmicin D (3), was identified as a new depsipeptide in the unnarmicin family, given its structural similarity to the existing compounds in this group. The planar structures of 1–3 were determined using 1D and 2D NMR spectra and complementary spectroscopic and spectrometric procedures. The absolute configurations of the amino acid components of 1–3 were determined via acid hydrolysis, derivitization with Marfey’s reagent and HPLC-UV comparison to authentic amino acid standards. The absolute configuration of the 3-hydroxydodecanoic acid moiety in 3 was determined using a modified Mosher’s esterification procedure on a linear derivative of tricharmicin (4) and additionally by a comparison of 13C NMR shifts of 3 to known depsipeptides with β-hydroxy acid subunits. Tricholide B (2) showed moderate cytotoxicity to Neuro-2A murine neuroblastoma cells (EC50: 14.5 ± 6.2 μM).

The Metabolome of a Cyanobacterial Bloom Visualized by MS/MS-Based Molecular Networking Reveals New Neurotoxic Smenamide Analogs (C, D, and E)

“…However, we did not observe nodes for trichophycin A or trichotoxins A and B. It should be noted that the macrocyclic polyketide-peptides tricholides A and B and unnarmicin D (Bertin et al, 2017a ) also clustered in the network (Figure 2 , Cluster 4). It may be that some metabolites in the bloom metabolome do not ionize well by ESI+ or give informative fragments during MS/MS acquisition; this represents a limitation in the implementation of MS/MS-based networking to describe bloom metabolomes.…”

“…In our previous work on Trichodesmium blooms and their natural products, we have utilized cytotoxicity assays, NMR-guided isolation, and MS-guided isolation (Bertin et al, 2016 , 2017a , b ; Belisle et al, 2017 ). We have previously characterized the cytotoxic polyketide trichophycin A, the polyketides trichotoxins A and B, and the moderately cytotoxic polyketide-peptide trichothiazole (Bertin et al, 2016 , 2017b ; Belisle et al, 2017 ).…”

“…Samples from a localized bloom of Trichodesmium were collected from Padre Island, Corpus Christi, TX during 9–11 May 2014 as described previously (Bertin et al, 2016 , 2017a , b ; Belisle et al, 2017 ). Briefly, bloom material was collected in 5-gallon buckets from ca .…”

“…In the current report, we detail the comprehensive metabolic profiling of a Trichodesmium bloom collected from the western Gulf of Mexico utilizing MS/MS-based molecular networking (Watrous et al, 2012 ; Yang et al, 2013 ; Wang et al, 2016 ) and cytotoxicity assays. In our previous work on this Trichodesmium bloom, we have utilized cytotoxicity assays, NMR-guided isolation and MS-guided isolation independently to characterize chlorinated polyketides and hybrid polyketide peptides (Bertin et al, 2016 , 2017a , b ; Belisle et al, 2017 ). The current report attempts to describe the Trichodesmium bloom metabolome more completely, focusing on a networking tool to cluster molecules based on similarities in the MS/MS fragmentation patterns (Watrous et al, 2012 ).…”

Trichothiazole A, a dichlorinated polyketide containing an embedded thiazole isolated from Trichodesmium blooms

“…4 Our laboratory has been intensively chemically profiling blooms of the cyanobacterium Trichodesmium collected from the Gulf of Mexico. Thus far we have characterized the chlorinated polyketides trichophycin A and trichotoxins A and B, 9,10 as well as the macrocyclic hybrid polyketide-peptides tricholides A and B and unnarmicin D. 11 We have employed bioassays and NMR examination to guide our isolations. However, having uncovered several chlorinated metabolites from bloom chemical fractions, 9,10 mass spectrometry-guided isolation offers means to ultimately purify metabolites based on molecular features identified from mass spectrometric isotopic data.…”