Screening of Secondary Metabolites Produced by Nigrospora sphaerica Associated with the Invasive Weed Cenchrus ciliaris Reveals Two New Structurally Related Compounds.

In the search for new alternative biocontrol strategies, phytopathogenic fungi could represent a new frontier for weed management. In this respect, as part of our ongoing work aiming at using fungal pathogens as an alternative to common herbicides, the foliar pathogen Nigrospora sphaerica has been evaluated to control buffelgrass (Cenchrus ciliaris). In particular, in this work, the isolation and structural elucidation of two new biosynthetically related metabolites, named nigrosphaeritriol (3-(hydroxymethyl)-2-methylpentane-1,4-diol) and nigrosphaerilactol (3-(1-hydroxyethyl)-4-methyltetrahydrofuran-2-ol), from the phytotoxic culture filtrate extract were described, along with the identification of several known metabolites. Moreover, the absolute stereochemistry of (3R,4S,5S)-nigrosphaerilactone, previously reported as (3S,4R,5R)-4-hydroxymethyl-3,5-dimethyldihydro-2-furanone, was determined for the first time by X-ray diffraction analysis. Considering their structural relationship, the determination of the absolute stereochemistry of nigrosphaerilactone allowed us to hypothesize the absolute stereochemistry of nigrosphaeritriol and nigrosphaerilactol.

A One-Pot Approach to Novel Pyridazine C-Nucleosides.

The synthesis of glycosides and modified nucleosides represents a wide research field in organic chemistry. The classical methodology is based on coupling reactions between a glycosyl donor and an acceptor. An alternative strategy for new C-nucleosides is used in this approach, which consists of modifying a pre-existent furyl aglycone. This approach is applied to obtain novel pyridazine C-nucleosides starting with 2- and 3-(ribofuranosyl)furans. It is based on singlet oxygen [4+2] cycloaddition followed by reduction and hydrazine cyclization under neutral conditions. The mild three-step one-pot procedure leads stereoselectively to novel pyridazine C-nucleosides of pharmacological interest. The use of acetyls as protecting groups provides an elegant direct route to a deprotected new pyridazine C-nucleoside.

7-hydroxytropolone is the main metabolite responsible for the fungal antagonism of Pseudomonas donghuensis strain SVBP6.

Pseudomonas donghuensis strain SVBP6, an isolate from an agricultural plot in Argentina, displays a broad-spectrum and diffusible antifungal activity, which requires a functional gacS gene but could not be ascribed yet to known secondary metabolites typical of Pseudomonas biocontrol species. Here, we report that Tn5 mutagenesis allowed the identification of a gene cluster involved in both the fungal antagonism and the production of a soluble tropolonoid compound. The ethyl acetate extract from culture supernatant showed a dose-dependent inhibitory effect against the phytopathogenic fungus Macrophomina phaseolina. The main compound present in the organic extract was identified by spectroscopic and X-ray analyses as 7-hydroxytropolone (7HT). Its structure and tautomerism was confirmed by preparing the two key derivatives 2,3-dimethoxy- and 2,7-dimethoxy-tropone. 7HT, but not 2,3- or 2,7-dimethoxy-tropone, mimicked the fungal inhibitory activity of the ethyl acetate extract from culture supernatant. The activity of 7HT, as well as its production, was barely affected by the presence of up to 50 µM added iron (Fe+2 ). To summarize, P. donghuensis SVBP6 produces 7HT under the positive control of the Gac-Rsm cascade and is the main active metabolite responsible for the broad-spectrum inhibition of different phytopathogenic fungi.

Pt(II) versus Pt(IV) in Carbene Glycoconjugate Antitumor Agents: Minimal Structural Variations and Great Performance Changes.

Octahedral Pt(IV) complexes (2Pt-R) containing a glycoconjugate carbene ligand were prepared and fully characterized. These complexes are structural analogues to the trigonal bipyramidal Pt(II) species (1Pt-R) recently described. Thus, an unprecedented direct comparison between the biological properties of Pt compounds with different oxidation states and almost indistinguishable structural features was performed. The stability profile of the novel Pt(IV) compounds in reference solvents was determined and compared to that of the analogous Pt(II) complexes. The uptake and antiproliferative activities of 2Pt-R and 1Pt-R were evaluated on the same panel of cell lines. DNA and protein binding properties were assessed using human serum albumin, the model protein hen egg white lysozyme, and double stranded DNA model systems by a variety of experimental techniques, including UV-vis absorption spectroscopy, fluorescence, circular dichroism, and electrospray ionization mass spectrometry. Although the compounds present similar structures, their in-solution stability, cellular uptake, and DNA binding properties are diverse. These differences may represent the basis of their different cytotoxicity and biological activity.

An Amphiphilic Pyridinoyl-hydrazone Probe for Colorimetric and Fluorescence pH Sensing.

A new pH sensor based on a substituted aroylhydrazide with a flexible side chain and a terminal trimethyl ammonium group (PHA+) was designed and synthesized. The terminal quaternary ammonium guarantees excellent solubility in water. At the same time, the probe is very soluble in hydrophobic envirornments. The pyridinoyl-hydrazone moiety acts as the pH-sensitive fluorophore/chromophore probe. Extensive physicochemical characterization has been performed on the bromide salt PHABr. DFT calculations, based on single-crystal X-ray data, permitted to rationalize the optical behavior. Molecular dynamics simulations permitted to clarify the mode of interaction with lipid membrane. The ability of the probe to change color and fluorescence in response to different pH and media of different polarity has been investigated. PHABr shows a remarkable pH-dependent behavior in both absorption and fluorescence spectra with high sensitivity and strong on-off switch effect at neutral pH, perceptible even to the naked eye.

Lentiquinones A, B, and C, Phytotoxic Anthraquinone Derivatives Isolated from Ascochyta lentis, a Pathogen of Lentil.

A strain of the pathogenic fungus Ascochyta lentis isolated from lentil ( Lens culinaris) was studied to ascertain its capability to produce bioactive metabolites. From the culture filtrates were found three new anthraquinone derivatives, named lentiquinones A (1), B (2), and C (3), and the known lentisone. From the mycelium, four known analogues were identified, namely pachybasin (in larger amount), ω-hydroxypachybasin, 1,7-dihydroxy-3-methylanthracene-9,10-dione, and phomarin. Lentiquinones A-C were characterized by spectroscopic methods as 3,4,6-trihydroxy-8-methyl-2 H-benzo[ g]chromene-5,10-dione, 2,3,4,5,10-pentahydroxy-7-methyl-3,4,4a,10-tetrahydroanthracen-9(2 H)-one, and its 2-epimer, respectively, and the relative configuration of the two latter compounds was deduced by X-ray diffraction data analysis. The absolute configuration of lentiquinones B and C was determined as (2 R,3 S,4 S,4a S,10 R) and (2 S,3 S,4 S,4a S,10 R), respectively, by electronic circular dichroism (ECD) in solution and solid state, and TDDFT calculations. When tested by using different bioassays, the novel compounds showed interesting activities. In particular, applied to punctured leaves of host and nonhost plants, the three new compounds and lentisone caused severe necrosis, with lentiquinone A being the most active among the new metabolites. On cress ( Lepidium sativum), this latter compound proved to be particularly active in inhibiting root elongation. On Lemna minor all the compounds reduced the content of chlorophyll, with 1,7-dihyroxy-3-methylanthracene-9,10-dione being the most active. The new compounds, together with lentisone, proved to have antibiotic properties.

AIE/ACQ Effects in Two DR/NIR Emitters: A Structural and DFT Comparative Analysis.

The effects of aggregation-induced emission (AIE) and of aggregation caused quenching (ACQ) were observed and discussed on two solid materials based on a phenylenevinylene (PV) and a dicyano-PV structure. The brightest emitter in solid films shows a high fluorescence quantum yield in the deep red/near IR (DR/NIR) region (75%). The spectroscopic properties of the two crystalline solids have been described and compared in terms of crystallographic data and time dependent DFT analysis. The influence of the cyano-substituents on AIE/ACQ mechanism activation was discussed.

Solid-State Highly Efficient DR Mono and Poly-dicyano-phenylenevinylene Fluorophores.

An efficient deep red (DR)-emitting organic solid based on a dicyano-phenylenevinylene derivative was reported. The structural and spectroscopic properties of the solid have been described in terms of crystallographic data and time-dependent DFT analysis. A noteworthy fluorescence quantum yield of 53% was observed for the brightest emitter cast into solid films. This result can be explained in terms of the aggregation-induced emission (AIE) effect.

Higginsianins A and B, Two Diterpenoid α-Pyrones Produced by Colletotrichum higginsianum, with in Vitro Cytostatic Activity.

Two new diterpenoid α-pyrones, named higginsianins A (1) and B (2), were isolated from the mycelium of the fungus Colletotrichum higginsianum grown in liquid culture. They were characterized as 3-[5a,9b-dimethyl-7-methylene-2-(2-methylpropenyl)dodecahydronaphtho[2,1-b]furan-6-ylmethyl]-4-hydroxy-5,6-dimethylpyran-2-one and 4-hydroxy-3-[6-hydroxy-5,8a-dimethyl-2-methylene-5-(4-methylpent-3-enyl)decahydronaphthalen-1-ylmethyl]-5,6-dimethylpyran-2-one, respectively, by using NMR, HRESIMS, and chemical methods. The structure and relative configuration of higginsianin A (1) were confirmed by X-ray diffractometric analysis, while its absolute configuration was assigned by electronic circular dichroism (ECD) experiments and calculations using a solid-state ECD/TDDFT method. The relative and absolute configuration of higginsianin B (2), which did not afford crystals suitable for X-ray analysis, were determined by NMR analysis and by ECD in comparison with higginsianin A. 1 and 2 were the C-8 epimers of subglutinol A and diterpenoid BR-050, respectively. The evaluation of 1 and 2 for antiproliferative activity against a panel of six cancer cell lines revealed that the IC50 values, obtained with cells reported to be sensitive to pro-apoptotic stimuli, are by more than 1 order of magnitude lower than their apoptosis-resistant counterparts (1 vs >80 µM). Finally, three hemisynthetic derivatives of 1 were prepared and evaluated for antiproliferative activity. Two of these possessed IC50 values and differential sensitivity profiles similar to those of 1.

Diplopimarane, a 20-nor-ent-pimarane produced by the oak pathogen Diplodia quercivora.

In this study a new 20-nor-ent-pimarane, named diplopimarane, was isolated together with sphaeropsidins A (9) and C (10), and (+)-epiepoformin (11) from organic crude extracts of Diplodia quercivora, a recently described oak pathogen originally found on declining Quercus canariensis trees in Tunisia. Diplopimarane was characterized as (1S,2R)-2,8,8-trimethyl-2-vinyl-1,2,3,4,5,6,7,8-octahydrophenanthrene-1,9,10-triol by spectroscopic, X-ray, optical, and chemical methods. It exhibited a wide range of activities including remarkable phytotoxicity on nonhost plants such as tomato cuttings, moderate antifungal activity against important plant pathogens, and moderate zootoxicity against Artemia salina. Its derivatives (2-4 and 6) were also tested for their phytotoxic and zootoxic activities. All these derivatives proved to be active against A. salina at 200 µg/mL, while 2 and 6 were also active on tomato cuttings. The other secondary metabolites (9, 10, and 11) herein reported for D. quercivora exhibited phytotoxic, antifungal, and zootoxic activity. This is the first report on the secondary metabolites secreted in vitro by this oak pathogen that could be key components of its adaptative strategies.

Chenopodolin: a phytotoxic unrearranged ent-pimaradiene diterpene produced by Phoma chenopodicola, a fungal pathogen for Chenopodium album biocontrol.

A new phytotoxic unrearranged ent-pimaradiene diterpene, named chenopodolin, was isolated from the liquid culture of Phoma chenopodicola, a fungal pathogen proposed for the biological control of Chenopodium album, a common worldwide weed of arable crops such as sugar beet and maize. The structure of chenopodolin was established by spectroscopic, X-ray, and chemical methods as (1S,2S,3S,4S,5S,9R,10S,12S,13S)-1,12-acetoxy-2,3-hydroxy-6-oxopimara-7(8),15-dien-18-oic acid 2,18-lactone. At a concentration of 2 mg/mL, the toxin caused necrotic lesions on Mercurialis annua, Cirsium arvense, and Setaria viride. Five derivatives were prepared by chemical modification of chenopodolin functionalities, and some structure-activity relationships are discussed.

2-(4-Methyl-phen-yl)-6-nitro-1,3-benzoxazole.

The title compound, C14H10N2O3, is a π-conjugated mol-ecule containing a benzoxazole aromatic fused heterobicycle. The benzoxazole ring system is planar within 0.01 Å. The mol-ecule assumes an approximately flat conformation, the benzoxazole ring system forming dihedral angles of 6.52 (12) and 7.4 (3)° with the benzene ring and the nitro group, respectively. In the crystal, mol-ecules are connected by very weak C-H⋯O hydrogen inter-actions, forming chains running parallel to the a or c axes. The methyl H atoms are disordered over two sets of sites of equal occupancy rotated by 60°.

3,3'-({4-[(4,5-Di-cyano-1H-imidazol-2-yl)diazen-yl]phen-yl}imino)-dipropionic acid.

The title compound, C17H15N7O4, is a push-pull non-linear optical chromophore containing a di-alkyl-amino donor group and the di-cyano-imidazolyl acceptor separated by a π-conjugated path. The benzene and imidazole rings are not coplanar, making a dihedral angle of 10.0 (2)°. In the crystal, mol-ecules are linked by an extended set of hydrogen bonds and several motifs are recognized. Pairs of mol-ecules are held together by hydrogen bonding between carb-oxy O-H donor groups and diazenyl N-atom acceptors, forming R 2 (2)(24) ring patterns across inversion centres. Four-mol-ecule R 4 (4)(28) ring motifs are formed, again across inversion centres, through hydrogen bonding involving carb-oxy O-H donor groups and diazenyl and imidazole N-atom acceptors. Four-mol-ecule R 4 (4)(42) patterns are formed among mol-ecules related by translation and involve carb-oxy O-H and imidazole N-H donor groups with carbonyl O-atom and imidazole N-atom acceptors.

Naphthalene-1,8-di-amine-2-(pyrimidin-2-yl)-1H-perimidine (2/1).

In the title adduct, C15H10N4·2C10H10N2, the pyrimidine ring is nearly co-planar with the heteroatomic perimidine ring, as indicated dihedral angle between their mean planes of 3.21 (11)°. The di-aminona-phthalene mol-ecules are slightly twisted [dihedral angles = 4.2 (2) and 3.0 (2)°] because of the steric encumbrance of NH2 groups. The perimidine and di-aminona-phthalene mol-ecules are linked by N-H⋯N hydrogen bonds, forming an R (4) 4(12) graph-set motif across an inversion center. In the crystal, alternating layers of the perimidine and di-aminona-phthalene mol-ecules are formed along [100]. In the perimidine layer, mol-ecules are π-π stacked along the c-axis direction with an inter-plane separation of approximately 3.4 Å.

{2-[2,2-Bis(4,4-dimethyl-4,5-di-hydro-1,3-oxazol-2-yl-κN)prop-yl]pyridine}-dichlorido-iron(II).

The title compound,[FeCl2(C18H25N3O2)], has a distorted tetra-hedral Cl2N2 coordination of the Fe(II) atom as a result of the constraints imposed by the 2-[2,2-bis-(4,4-dimethyl-4,5-di-hydro-1,3-oxazol-2-yl)prop-yl]pyridine ligand. The pyridine ring is almost perpendicular to the six-membered chelated ring containing the metal atom [dihedral angle between their mean planes = 88.5 (1)°].

(3S,3aS,6R,6aR)-2-Oxohexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate.

The title compound, C20H16O7, contains a cis-fused γ-lactone tetra-hydro-furan ring system functionalized with two benzo-yloxy groups. Both rings adopt an envelope conformation. The mol-ecule assumes an elongated shape and exibits non-crystallographic C 2 symmetry. The benzo-yloxy groups are almost planar [maximum deviations of 0.0491 (15) and 0.0336 (17) Šfor the O atoms] and their mean planes are inclined to one another by 16.51 (4)°. The crystal packing features weak C-H⋯O inter-actions. The aryl groups of adjacent mol-ecules are parallel shifted with face-to-face contacts and a shortest inter-molecular C⋯C distance of 3.482 (4) Å.

Dipentyl 2,6-di-amino-benzo[1,2-b:4,5-b']di-furan-3,7-di-carboxyl-ate.

The title compound, C22H28N2O6, crystallizes with one half-mol-ecule in the independent unit, the mol-ecule being located on an inversion centre. The penthyl groups are in the all-trans conformation and an almost planar conformation of the whole mol-ecule is observed [maximum deviation from the least-squares plane through all non-H atoms is 0.0229 (17) Šfor an N atom]. The amino groups are involved in intra- and inter-molecular hydrogen bonds. Intra-molecular hydrogen bonding involving the amino group and ester carbonyl helps to lock the syn conformation of the ester with respect to the amino group. In the crystal, N-H⋯O hydrogen bonding involving the amino group and the furan and ester carbonyl O atoms self-assembles the mol-ecules into a two-dimensional hydrogen-bonded network parallel to (010) that displays inter-digital packing sustained by alk-yl-alkyl inter-actions.

3ß,6ß-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one acetic acid 0.04-solvate.

The title compound, C31H48O7·0.04CH3COOH, is a polyoxy-genated steroid obtained by selective chemical oxidation of 7-de-hydro-cholesteryl acetate. The asymmetric unit comprises three mol-ecules of the steroid (Z' = 3) and a mol-ecule of acetic acid which has occupancy factor 0.131 (5). The geometric parameters of the independent mol-ecules do not reveal significant differences. In one mol-ecule, the terminal isopropyl group is disordered over two sets of sites with occupancy ratio 0.869 (5):0.131 (5). The three mol-ecules reveal different hydrogen-bonding patterns. Each of them is involved in an intra-molecular S(6) hydrogen-bonding motif, involving hy-droxy groups as donor and acceptor. In the crystal, two independent mol-ecules form dimers through hydrogen bonding between an OH donor and an acetate carbonyl acceptor, giving rise to R 2 (2)(16) ring patterns. A single hydrogen bond between the OH group and a ketone carbonyl group is observed between two symmetry-independent mol-ecules.

(3R,3aR,6R,6aR)-Hexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate.

The title compound, C20H18O6, prepared from d-mannitol by a two-step procedure, is a functionalized fused bis-tetra-hydro-furan. In the central fragment, consisting of two fused tetra-hydro-furan rings, one O atom and its two adjacent C atoms, a methyl-ene and a bridgehead C atom, are disordered over two sets of sites with an occupancy ratio of 0.735 (9):0.265 (9). In the major component, the ring containing the disordered O atom is a half-chair conformation with twisted methylene and benzoate-substituted C atoms, whereas the other ring has a half-chair or T-form conformation. In the minor component, the ring with the disordered O atom has an envelope conformation, with the O atom as the flap, and the other ring has a half-chair conformation, with the O atom and the other bridgehead CH atom being twisted. The two aromatic rings are inclined to one another by 20.00 (12)°. In the crystal, adjacent molecules are linked via C-H⋯π interactions, forming chains propagating along [010].

3ß,6α-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one.

The title compound, C31H48O7, a polyoxygenated steroid, was obtained by chemical oxidation of 7-de-hydro-cholesteryl acetate. The mol-ecular geometry features trans A/B and C/D junctions at the steroid core with the acetyl groups in the equatorial position and a fully extended conformation for the alkyl side chain. A chair conformation is observed for rings A and C while ring B adopts a half-chair conformation. The five-membered ring D has an envelope conformation, with the C atom bearing the methyl group at the flap. The terminal isopropyl group and one acetyl group are disordered over two sets of sites with 0.774 (8):0.226 (8) and 0.843 (7):0.157 (7) ratios, respectively. An intra-molecular S(6) O-H⋯O hydrogen-bonding motif involving a hy-droxy donor and acceptor is observed. In the crystal, chains of mol-ecules running along the b axis are formed via O-H⋯O hydrogen bonds between hy-droxy donors and carbonyl acceptors of the ordered acetyl group, giving rise to a C(14) motif. The chains are wrapped around the 21 screw axes.