Abstract
Three new cyanobactins, trikoramides B (1)–D (3), have been isolated from the marine cyanobacterium, Symploca hydnoides, following a preliminary bioassay-guided isolation of the two most active polar fractions based on the brine shrimp toxicity assay. These new cyanobactins are new analogues of the previously reported cytotoxic trikoramide A (4) with differences mainly in the C-prenylated cyclotryptophan unit. Their planar structures were elucidated from their 1D and 2D NMR spectral data in combination with the HRMS/MS data. Marfey’s method, 2D NOESY NMR spectroscopic and ECD spectra analyses were used to determine the absolute stereochemistry of trikoramides B (1)–D (3). Trikoramides B (1) and D (3) exhibited cytotoxicity against MOLT-4 acute lymphoblastic leukemia cell line with IC50 values of 5.2 µM and 4.7 µM, respectively. Compounds 1 and 3 were also evaluated for their quorum-sensing inhibitory assay based on the Pseudomonas aeruginosa PAO1 lasB-gfp and rhlA-gfp bioreporter strains. Although trikoramide B (1) exhibited weak quorum-sensing inhibitory activity, the Br-containing trikoramide D (3) exhibited moderate to significant dose-dependent quorum-sensing inhibitory activities against PAO1 lasB-gpf and rhlA-gfp bioreporter strains with IC50 values of 19.6 µM and 7.3 µM, respectively.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Further chemical investigation on the brine shrimp toxic polar VLC fractions obtained from the CH2 Cl2 -MeOH (2:1) extracts of the marine cyanobacterium, S. hydnoides, from
B [25,26], trikoramide A [10] and motobamide A [12] which have all been isolated from cyanobacteria
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The order Oscillatoriales accounts to produce most of the isolated bioactive secondary metabolites from marine cyanobacteria, most of which are cyclic or linear peptides [2]. These peptides are assembled by either the nonribosomal or post-translationally modified ribosomal biosynthetic pathways in cyanobacteria. Further investigations into the brine shrimp toxic polar fractions have afforded three new related compounds, trikoramides B (1)–D (3) Both trikoramides B (1) and D (3) exhibited significant cytotoxic activity against MOLT-4 acute lymphoblastic leukemia cell line. Mar. Drugs 2021, 19, 548 quorum-sensing inhibitory (QSI) activities in a dose-dependent manner when tested in the Pseudomonas aeruginosa PAO1 lasB-gpf and rhlA-gfp bioreporter strains.
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