Chloride Ligands on DNA-Stabilized Silver Nanoclusters.

DNA-stabilized silver nanoclusters (AgN-DNAs) are known to have one or two DNA oligomer ligands per nanocluster. Here, we present the first evidence that AgN-DNA species can possess additional chloride ligands that lead to increased stability in biologically relevant concentrations of chloride. Mass spectrometry of five chromatographically isolated near-infrared (NIR)-emissive AgN-DNA species with previously reported X-ray crystal structures determines their molecular formulas to be (DNA)2[Ag16Cl2]8+. Chloride ligands can be exchanged for bromides, which red-shift the optical spectra of these emitters. Density functional theory (DFT) calculations of the 6-electron nanocluster show that the two newly identified chloride ligands were previously assigned as low-occupancy silvers by X-ray crystallography. DFT also confirms the stability of chloride in the crystallographic structure, yields qualitative agreement between computed and measured UV-vis absorption spectra, and provides interpretation of the 35Cl-nuclear magnetic resonance spectrum of (DNA)2[Ag16Cl2]8+. A reanalysis of the X-ray crystal structure confirms that the two previously assigned low-occupancy silvers are, in fact, chlorides, yielding (DNA)2[Ag16Cl2]8+. Using the unusual stability of (DNA)2[Ag16Cl2]8+ in biologically relevant saline solutions as a possible indicator of other chloride-containing AgN-DNAs, we identified an additional AgN-DNA with a chloride ligand by high-throughput screening. Inclusion of chlorides on AgN-DNAs presents a promising new route to expand the diversity of AgN-DNA structure-property relationships and to imbue these emitters with favorable stability for biophotonics applications.

NMR spectroscopic discrimination of the enantiomer pairs of soman and bispinacolyl-methylphosphonate and detailed analysis of the pinacolyl group 1 H NMR resonances.

If a 1 H NMR FID measured from oman is manipulated with Gaussian windowing before Fourier transformation, nine protons' signals of pinacolyl group can show some shape depending on the solvent and temperature. How could those signals shape and separate soman isomers as well as conformers information be combined, or could they fit somehow? Molecular modeling results together with accurate iterative spectral analysis were also extended to bispinacolyl-methylphoshonate (BPMP), which have two pinacolyl groups. As far as we know, this is the first complete 1 H, 13 C, and 31 P NMR spectral analysis of BPMP.

Alternative Biosynthetic Starter Units Enhance the Structural Diversity of Cyanobacterial Lipopeptides.

Puwainaphycins (PUWs) and minutissamides (MINs) are structurally analogous cyclic lipopeptides possessing cytotoxic activity. Both types of compound exhibit high structural variability, particularly in the fatty acid (FA) moiety. Although a biosynthetic gene cluster responsible for synthesis of several PUW variants has been proposed in a cyanobacterial strain, the genetic background for MINs remains unexplored. Herein, we report PUW/MIN biosynthetic gene clusters and structural variants from six cyanobacterial strains. Comparison of biosynthetic gene clusters indicates a common origin of the PUW/MIN hybrid nonribosomal peptide synthetase and polyketide synthase. Surprisingly, the biosynthetic gene clusters encode two alternative biosynthetic starter modules, and analysis of structural variants suggests that initiation by each of the starter modules results in lipopeptides of differing lengths and FA substitutions. Among additional modifications of the FA chain, chlorination of minutissamide D was explained by the presence of a putative halogenase gene in the PUW/MIN gene cluster of Anabaena minutissima strain UTEX B 1613. We detected PUW variants bearing an acetyl substitution in Symplocastrum muelleri strain NIVA-CYA 644, consistent with an O-acetyltransferase gene in its biosynthetic gene cluster. The major lipopeptide variants did not exhibit any significant antibacterial activity, and only the PUW F variant was moderately active against yeast, consistent with previously published data suggesting that PUWs/MINs interact preferentially with eukaryotic plasma membranes.IMPORTANCE Herein, we deciphered the most important biosynthetic traits of a prominent group of bioactive lipopeptides. We reveal evidence for initiation of biosynthesis by two alternative starter units hardwired directly in the same gene cluster, eventually resulting in the production of a remarkable range of lipopeptide variants. We identified several unusual tailoring genes potentially involved in modifying the fatty acid chain. Careful characterization of these biosynthetic gene clusters and their diverse products could provide important insight into lipopeptide biosynthesis in prokaryotes. Some of the variants identified exhibit cytotoxic and antifungal properties, and some are associated with a toxigenic biofilm-forming strain. The findings may prove valuable to researchers in the fields of natural product discovery and toxicology.

Complete 1 H, 13 C{1 H}, and 31 P NMR spectral parameters of some pyrophosphates.

The 1 H, 13 C{1 H}, and 31 P NMR spectral parameters of some pyrophosphates were determined in CDCl3 . The most complicated 1 H spectrum can be solved fully only as (A3 MN)R6 XX'R6 '(MNA3 )', where R6 (= -N(CH3 )2 ) is coupled only to phosphorus (X). Second-order coupling between phosphorus was found and solved with iterative analysis. A signal shape of one of the carbon resonance cannot be explained only with couplings. Explanation for exceptional shape was searched from molecular modeling results. Copyright © 2017 John Wiley & Sons, Ltd.

Substituent effect in 2-benzoylmethylenequinoline difluoroborates exhibiting through-space couplings. Multinuclear magnetic resonance, X-ray diffraction, and computational study.

The series of nine 2-benzoylmethylenequinoline difluoroborates have been synthesized and characterized by multinuclear magnetic resonance, X-ray diffraction (XRD), and computational methods. The through-space spin-spin couplings between (19)F and (1)H/(13)C nuclei have been observed in solution. The NMR chemical shifts have been correlated to the Hammett substituent constants. The crystal structures of six compounds have been solved by XRD. For two derivatives the X-ray wave function refinement was performed to evaluate the character of bonds in the NBF(2)O moiety by topological and integrated bond descriptors.

2-Acylamino- and 2,4-bis(acylamino)pyrimidines as supramolecular synthons analyzed by multiple noncovalent interactions. DFT, X-ray diffraction, and NMR spectral studies.

Intermolecular interactions of ten 2-acylamino and 2,4-bis(acylamino)pyrimidines (7 of which are previously unknown) have been investigated by X-ray structural, quantum chemical (DFT), and NMR spectral methods. Especially the concentration dependencies of the (1)H NMR chemical shifts and titrations with other molecules capable of multiple hydrogen bonding provided useful information regarding their association via triple or quadruple hydrogen bonding, which is controlled by the conformational preferences of 2-acylamino- and 2,4-bis(acylamino)pyrimidines. On comparison of the properties of 2-acylamino- and 2,4-bis(acylamino)pyrimidines with the corresponding pyridines, an additional nitrogen in the heterocyclic ring is the crucial factor in explaining the stability of various conformers and dimers of pyrimidines. Computational modeling of their dimerization (self-association) and heteroassociation supports the experimental findings. The substituent effects in 2-acylamino- and 2,4-bis(acylamino)pyrimidines are discussed via inter- and intramolecular terms. The subtle balance between several structural factors and their influence on the aggregation of studied pyrimidines was confirmed also by variable-temperature NMR and NOE experiments. X-ray structures of 2-methyl- and 2-adamantyl-CONH-pyrimidines revealed very different intermolecular interactions, showing the importance of the substituent size on the self-assembly process. As a whole NMR spectral, X-ray structural, and computational data of 2-acylamino- and 2,4-bis(acylamino)pyrimidines can be interpreted in terms of multiple intra-/intermolecular interactions.

1H and 13C{1H} NMR spectral parameters of sulfur mustards, nitrogen mustards, and lewisites: computing and predicting of reference spectra for chemical identification.

The (1)H and (13)C{(1)H} chemical shifts and (1)H spin-spin couplings of sulfur mustards, nitrogen mustards, and lewisites scheduled in the Chemical Weapons Convention, and those of bis(2-chloromethyl)disulfide, were determined in CDCl(3), CD(2)Cl(2), and (CD(3))(2)CO. Accurate parameters of this kind of series can be used for evaluating the current molecular modeling programs and the chemical shift and coupling constant prediction possibilities of the programs. Several prediction tests were made with commercial programs, and the results are reported here.

Discovery of a Pederin Family Compound in a Nonsymbiotic Bloom-Forming Cyanobacterium.

The pederin family includes a number of bioactive compounds isolated from symbiotic organisms of diverse evolutionary origin. Pederin is linked to beetle-induced dermatitis in humans, and pederin family members possess potent antitumor activity caused by selective inhibition of the eukaryotic ribosome. Their biosynthesis is accomplished by a polyketide/nonribosomal peptide synthetase machinery employing an unusual trans-acyltransferase mechanism. Here, we report a novel pederin type compound, cusperin, from the free-living cyanobacterium Cuspidothrix issatschenkoi (earlier Aphanizomenon). The chemical structure of cusperin is similar to that of nosperin recently isolated from the lichen cyanobiont Nostoc sharing the tehrahydropyran moiety and major part of the linear backbone. However, the cusperin molecule is extended by a glycine residue and lacks one hydroxyl substituent. Pederins were previously thought to be exclusive to symbiotic relationships. However, C. issatschenkoi is a nonsymbiotic planktonic organism and a frequent component of toxic water blooms. Cusperin is devoid of the cytotoxic activity reported for other pederin family members. Hence, our findings raise questions about the role of pederin analogues in cyanobacteria and broaden the knowledge of ecological distribution of this group of polyketides.

Production of High Amounts of Hepatotoxin Nodularin and New Protease Inhibitors Pseudospumigins by the Brazilian Benthic Nostoc sp. CENA543.

Nostoc is a cyanobacterial genus, common in soils and a prolific producer of natural products. This research project aimed to explore and characterize Brazilian cyanobacteria for new bioactive compounds. Here we report the production of hepatotoxins and new protease inhibitors from benthic Nostoc sp. CENA543 isolated from a small, shallow, saline-alkaline lake in the Nhecolândia, Pantanal wetland area in Brazil. Nostoc sp. CENA543 produces exceptionally high amounts of nodularin-R. This is the first free-living Nostoc that produces nodularin at comparable levels as the toxic, bloom-forming, Nodularia spumigena. We also characterized pseudospumigins A-F, which are a novel family of linear tetrapeptides. Pseudospumigins are structurally related to linear tetrapeptide spumigins and aeruginosins both present in N. spumigena but differ in respect to their diagnostic amino acid, which is Ile/Leu/Val in pseudospumigins, Pro/mPro in spumigins, and Choi in aeruginosins. The pseudospumigin gene cluster is more similar to the spumigin biosynthetic gene cluster than the aeruginosin gene cluster. Pseudospumigin A inhibited trypsin (IC50 4.5 µM after 1 h) in a similar manner as spumigin E from N. spumigena but was almost two orders of magnitude less potent. This study identifies another location and environment where the hepatotoxic nodularin has the potential to cause the death of eukaryotic organisms.