Effects of Halide Ions on the Carbamidocyclophane Biosynthesis in Nostoc sp. CAVN2

Abstract

In this study, the influence of halide ions on [7.7]paracyclophane biosynthesis in the cyanobacterium Nostoc sp. CAVN2 was investigated. In contrast to KI and KF, supplementation of the culture medium with KCl or KBr resulted not only in an increase of growth but also in an up-regulation of carbamidocyclophane production. LC-MS analysis indicated the presence of chlorinated, brominated, but also non-halogenated derivatives. In addition to 22 known cylindrocyclophanes and carbamidocyclophanes, 27 putative congeners have been detected. Nine compounds, carbamidocyclophanes M−U, were isolated, and their structural elucidation by 1D and 2D NMR experiments in combination with HRMS and ECD analysis revealed that they are brominated analogues of chlorinated carbamidocyclophanes. Quantification of the carbamidocyclophanes showed that chloride is the preferably utilized halide, but incorporation is reduced in the presence of bromide. Evaluation of the antibacterial activity of 30 [7.7]paracyclophanes and related derivatives against selected pathogenic Gram-positive and Gram-negative bacteria exhibited remarkable effects especially against methicillin- and vancomycin-resistant staphylococci and Mycobacterium tuberculosis. For deeper insights into the mechanisms of biosynthesis, the carbamidocyclophane biosynthetic gene cluster in Nostoc sp. CAVN2 was studied. The gene putatively coding for the carbamoyltransferase has been identified. Based on bioinformatic analyses, a possible biosynthetic assembly is discussed.

Enzymatic Halogenation and Dehalogenation Reactions: Pervasive and Mechanistically Diverse

“…A recent report describing the structure elucidation and biosynthetic gene cluster discovery of cyanobacterial bartolosides has uncovered a potentially novel diiron-dependent halogenase, 430,431 with homologs present in other cyanobacteria, including in a cyanobacterial gene cluster encoding the production of structurally analogous halogenated cyclophane natural products. 432 Furthermore, a recent report challenges our understanding of the catalytic scope of FDHs which were previously thought to only halogenate aromatic rings or electron rich activated aliphatic carbon centers. Discovery and characterization of a fungal bifunctional methyltransferase-halogenase enzyme established the gem-dichlorination on a non-activated carbon atom, 433 a transformation previously within the realm of NHFe halogenases proceeding with the halide radical route.…”

Discovery of Unusual Biaryl Polyketides by Activation of a SilentStreptomyces venezuelaeBiosynthetic Gene Cluster

“…Halogenation of an atural product can significantly affect its biological activity,i ncluding its antibacterial activity. [37][38][39] We thus investigated the activity of culture supernatants of M1835 containing venemycin, and its monochlorinated and monobrominatedd erivatives,a gainst Micrococcus luteus and E. coli,b ut no growth inhibition was observed (data not shown).…”

Divergent Synthesis of Novel Cylindrocyclophanes that Inhibit Methicillin‐Resistant Staphylococcus aureus (MRSA)

“…To our knowledge, all studies to date describing the antibacterial evaluation of the cylindrocyclophane family are restricted to naturally occurring [7.7]paracyclophanes of which 16 members have been identified. [32,33] This limits the chemical diversity and hence scope of any such investigation, meaning that little is known about the structure-activity relationships of these compounds or their derivatives. The cylindrofridins (linear congeners of the cylindrocyclophanes) display reduced activity against MRSA and Streptococcus pneumoniae, thus suggesting that cyclisation augments the antibacterial activity of this scaffold.…”

“…[32] The cylindrocyclophane α-OH motif is not required for activity against Mycobacterium tuberculosis, although α-acetylated cylindrocyclophanes display reduced activity against MRSA. [33] These observations prompted us to question which structural motifs might be responsible for the antibacterial activity of the cylindrocyclophanes. We thought it possible that we could design cylindrocyclophane analogues with streamlined syntheses that retain the antibacterial activity of the parent scaffold.…”