The priming molecule ß-aminobutyric acid is naturally present in plants and is induced by stress.

The defense system of a plant can be primed for increased defense, resulting in an augmented stress resistance and/or tolerance. Priming can be triggered by biotic and abiotic stimuli, as well as by chemicals such as ß-aminobutyric acid (BABA), a nonprotein amino acid considered so far a xenobiotic. Since the perception mechanism of BABA has been recently identified in Arabidopsis thaliana, in the present study we explored the possibility that plants do synthesize BABA. After developing a reliable method to detect and quantify BABA in plant tissues, and unequivocally separate it from its two isomers α- and γ-aminobutyric acid, we measured BABA levels in stressed and nonstressed A. thaliana plants, and in different plant species. We show that BABA is a natural product of plants and that the endogenous levels of BABA increase rapidly after infection with necrotrophic, biotrophic and hemibiotrophic pathogens, as well as after salt stress and submergence. Our results place the rise in endogenous BABA levels to a point of convergence in plant stress response and provide biological significance to the presence of a receptor in plants. These findings can explain the extremely widespread efficacy of BABA and open the way to unravel the early steps of priming.

Columnar self-assembly of N,N',N''-trihexylbenzene-1,3,5-tricarboxamides investigated by means of NMR spectroscopy and computational methods in solution and the solid state.

The columnar self-assembly resulting from units of N,N',N''-trihexylbenzene-1,3,5-tricarboxamide is investigated in solution and the solid state by means of NMR spectroscopy. A parallel computational study utilizing both semiempirical and DFT methods allows comparison between experimental results and calculated data for self-assembled and non-assembled structural hypotheses. The hybrid functional B3LYP is compared with the B3LYP-D and B97D functionals to assess contributions due to dispersion interactions. Interatomic distances are studied utilizing ROE experiments on proton spins in solution. Isotropic shifts as measured experimentally are shown to offer a method to assess the self-assemblies 'on-the-fly'. The anisotropic part of the shift interaction for carbon nuclei is probed in the solid state with specific magic-angle spinning experiments. The sensitivity of the NMR parameters for various carbon environments with respect to the orientation of the substituents and packing effects is investigated computationally. We show that all the utilized experimental techniques, in both solution and the solid state, and in combination with DFT calculations, are capable of discerning between assembled and non-assembled systems and offer a robust set of independent tools to highlight atomic details in self-organized structures.

Real-time amyloid aggregation monitoring with a photonic crystal-based approach.

We propose the application of a new label-free optical technique based on photonic nanostructures to real-time monitor the amyloid-beta 1-42 (Aß(1-42)) fibrillization, including the early stages of the aggregation process, which are related to the onset of the Alzheimer's Disease (AD). The aggregation of Aß peptides into amyloid fibrils has commonly been associated with neuronal death, which culminates in the clinical features of the incurable degenerative AD. Recent studies revealed that cell toxicity is determined by the formation of soluble oligomeric forms of Aß peptides in the early stages of aggregation. At this phase, classical amyloid detection techniques lack in sensitivity. Upon a chemical passivation of the sensing surface by means of polyethylene glycol, the proposed approach allows an accurate, real-time monitoring of the refractive index variation of the solution, wherein Aß(1-42) peptides are aggregating. This measurement is directly related to the aggregation state of the peptide throughout oligomerization and subsequent fibrillization. Our findings open new perspectives in the understanding of the dynamics of amyloid formation, and validate this approach as a new and powerful method to screen aggregation at early stages.

2-[2-(pyrrolidin-2-yl)propan-2-yl]-1H-pyrrole and its amide derivative 1-{2-[2-(1H-pyrrol-2-yl)propan-2-yl]pyrrolidin-1-yl}ethanone.

In the title compounds, C(11)H(18)N(2), (II), and C(13)H(20)N(2)O, (III), the pyrrolidine rings have twist conformations. Compound (II) crystallizes with two independent molecules (A and B) in the asymmetric unit. The mean planes of the pyrrole and pyrrolidine rings are inclined to one another by 89.99 (11) and 89.35 (10)° in molecules A and B, respectively. In (III), the amide derivative of (II), the same dihedral angle is much smaller, at only 13.42 (10)°. In the crystal structure of (II), the individual molecules are linked via N-H...N hydrogen bonds to form inversion dimers, each with an R(2)(2)(12) graph-set motif. In the crystal structure of (III), the molecules are linked via N-H...O hydrogen bonds to form inversion dimers with an R(2)(2)(16) graph-set motif.

2,2'-[(2S*,6R*)-Piperidine-2,6-di-yl]-di-pro-pan-2-ol.

In the title compound, C(11)H(23)NO(2), the piperidine ring has a chair conformation. The two hy-droxy H atoms are disordered over two positions with fixed occupancy ratios of 0.57:0.43 and 0.63:0.37. In the mol-ecule, there are two short N-H⋯O inter-actions. In the crystal, four symmetry-related mol-ecules are linked by O-H⋯O hydrogen bonds to form a cage-like arrangement, centered about the point of inter-section of three twofold axes. These cages stack along the [100] direction.

4-Meth-oxy-benzoyl-meso-octa-methyl-calix[2]pyrrolidino[2]pyrrole: an acyl chloride derivative of a partially reduced calix[4]pyrrole.

In the title compound, C(36)H(50)N(4)O(2), the two pyrrolidine rings have envelope conformations. The conformation of the macrocycle is stabilized by N-H⋯N hydrogen bonds and a C-H⋯N inter-action. The benzoyl ring is inclined to an adjacent pyrrole ring by 6.76 (9)°, with a centroid-to-centroid distance of 3.6285 (10) Å. In the crystal, apart from a C-H⋯O and a C-H⋯π inter-action, mol-ecules are linked via an N-H⋯O hydrogen bond, leading to the formation of helical chains propagating along [010].

4-Chloro-benzoyl-meso-octa-methyl-calix[2]pyrrolidino[2]pyrrole: an acyl chloride derivative of a partially reduced calix[4] pyrrole.

In the title compound, C(35)H(47)ClN(4)O, the two pyrrolidine rings have envelope conformations. The conformation of the macrocycle is stabilized by N-H⋯N hydrogen bonds and a C-H⋯N inter-action. The benzoyl ring is inclined to the adjacent pyrrole ring by 11.66 (11)°, with a centroid-centroid distance of 3.7488 (13) Å. In the crystal, molecules are linked by N-H⋯O hydrogen bonds into helical chains propagating in [010] and C-H⋯O and C-H⋯π interactions are also observed.

Catalytic hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole).

Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.

2,2'-(Propane-2,2-di-yl)bis-(1H-pyrrole).

The title compound, C(11)H(14)N(2), crystallized with two independent mol-ecules (A and B) in the asymmetric unit. The two mol-ecules differ only slightly, with the pyrrole rings being inclined to one another at a dihedral angle of 87.67 (8)° in mol-ecule A and 88.09 (7)° in mol-ecule B. In the crystal, there are no classical hydrogen bonds, but the two pyrrole NH groups of one mol-ecule are involved in N-H⋯π inter-actions with the pyrrole rings of the other mol-ecule. In this manner, a compact box-like arrangement of the two independent mol-ecules is formed.

4,4-Bis(1H-pyrrol-2-yl)penta-nol.

The title achiral compound, C(13)H(18)N(2)O, crystallized in the chiral monoclinic space group P2(1). The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in inter-molecular N-H⋯O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An inter-esting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydr-oxy H atom. There is, however, a weak inter-molecular O-H⋯π inter-action involving one of the pyrrole rings.

2-(2-Naphth-yl)-1,3-dioxane.

The title compound, C(14)H(14)O(2), crystallizes in the chiral monoclinic space group P2(1). This acetal is composed of a planar naphthalene ring with a 1,3-dioxane ring substituent, which has a chair conformation. In the crystal structure, symmetry-related mol-ecules are connected via a weak C-H⋯O inter-action to form a helical chain propagating in [010]. While there are no π-π stacking inter-actions present, there are weak C-H⋯π inter-actions involving the naphthalene aromatic rings, which link the helical chains to form a two-dimensional network in the (011) plane.

1,4-Bis[4-(tert-butyl-diphenyl-silyl)buta-1,3-diyn-yl]benzene.

The title centrosymmetric mol-ecule, C(46)H(42)Si(2), is composed of a central benzene ring with buta-1,3-diynyl chains at positions 1 and 4. These chains are terminated by tert-butyl-diphenyl-silyl groups, hence the molecule is dumbbell in shape. The mol-ecules are connected via C-H⋯π inter-actions in the structure, so forming an undulating two-dimensional network in the bc plane. There is also a weak π-π inter-action involving centrosymmetrically related phenyl rings with a centroid-centroid distance of 3.8359 (11) Å.

1,4-Bis(hex-yloxy)-2,5-diiodo-benzene.

The centrosymmetric title compound, C(18)H(28)I(2)O(2), crystallized in the monoclinic space group P2(1)/c with the alkyl chains having extended all-trans conformations, similar to those in the centrosymmetric bromo analogue [Li et al. (2008 ▶). Acta Cryst. E64, o1930] that crystallized in the triclinic space group P. The difference between the two structures lies in the orientation of the two alkyl chains with respect to the C(aromatic)-O bond. In the title compound, the O-C(alk-yl)-C(alk-yl)-C(alk-yl) torsion angle is 55.8 (5)°, while in the bromo analogue this angle is -179.1 (2)°. In the title compound, the C-atoms of the alkyl chain are almost coplanar [maximum deviation of 0.052 (5) Å] and this mean plane is inclined to the benzene ring by 50.3 (3)°. In the bromo-analogue, these two mean planes are almost coplanar, making a dihedral angle of 4.1 (2)°. Another difference between the crystal structures of the two compounds is that in the title compound there are no halide⋯halide inter-actions. Instead, symmetry-related mol-ecules are linked via C-H⋯π contacts, forming a two-dimensional network.

5-Hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate: diastereoselectivity of the Mukaiyama crossed-aldol-type reaction.

The title compounds, rac-(1'R,2R)-tert-butyl 2-(1'-hydroxyethyl)-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(17)H(20)N(2)O(6), (I), rac-(1'S,2R)-tert-butyl 2-[1'-hydroxy-3'-(methoxycarbonyl)propyl]-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(20)H(24)N(2)O(8), (II), and rac-(1'S,2R)-tert-butyl 2-(4'-bromo-1'-hydroxybutyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(13)H(20)BrNO(4), (III), are 5-hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydropyrrole-1-carboxylate. In all three compounds, the tert-butoxycarbonyl (Boc) unit is orientated in the same manner with respect to the mean plane through the 2-oxo-2,5-dihydro-1H-pyrrole ring. The hydroxyl substituent at one of the newly created chiral centres, which have relative R,R stereochemistry, is trans with respect to the oxo group of the pyrrole ring in (I), synthesized using acetaldehyde. When a larger aldehyde was used, as in compounds (II) and (III), the hydroxyl substituent was found to be cis with respect to the oxo group of the pyrrole ring. Here, the relative stereochemistry of the newly created chiral centres is R,S. In compound (I), O-H...O hydrogen bonding leads to an interesting hexagonal arrangement of symmetry-related molecules. In (II) and (III), the hydroxyl groups are involved in bifurcated O-H...O hydrogen bonds, and centrosymmetric hydrogen-bonded dimers are formed. The Mukaiyama crossed-aldol-type reaction was successful when using the 2-nitrophenyl-substituted hydroxypyrrole, or the unsubstituted hydroxypyrrole, and boron trifluoride diethyl ether as catalyst. The synthetic procedure leads to a syn configuration of the two newly created chiral centres in all three compounds.

rac-Methyl 4-azido-3-hydr-oxy-3-(2-nitro-phen-yl)butanoate.

In the title compound, C(11)H(12)N(4)O(5), the mean plane through the nitro substituent on the benzene ring is inclined to the benzene mean plane by 85.8 (2)°, which avoids steric inter-actions with the ortho substituents. The hydr-oxy group is involved in bifurcated hydrogen bonds. The first is an intra-molecular O-H⋯O hydrogen bond, involving the ester carbonyl O atom, which gives rise to the formation of a boat-like hydrogen-bonded chelate ring. The second is an inter-molecular O-H⋯N hydrogen bond involving the first N atom of the azide group of a symmetry-related mol-ecule. In the crystal structure this leads to the formation of a polmer chain extending in the c-axis direction.

Synthesis, structure, and complexation properties of partially and completely reduced meso-octamethylporphyrinogens (calix[4]pyrroles).

New tricks for an old dog: Calixpyrroles bind anions efficiently and can be transformed into transition-metal complexes only under forcing conditions. Reducing the macrocycle creates a ligand that easily forms classical Werner complexes with copper, nickel, and palladium ions. The metal complexes present an array of four directed hydrogen bonds, which specifically bind the counterions (see picture; blue N, white H, green Cl, red Cu, Ni, or Pd).

Glycoside esters of 5-aminolevulinic acid for photodynamic therapy of cancer.

Aliphatic and ethylene glycol esters of 5-aminolevulinic acid (ALA) are very efficient precursors of the photosensitizer protoporphyrin IX (PpIX) for photodynamic therapy; however, they diffuse passively across the cell membrane and thus lack cell selectivity. We evaluated whether alpha-glucose, alpha-mannose, or beta-galactose esters of ALA would present improved properties as precursors of PpIX. Esterification was performed either at the position O-1 or O-6 of the sugars with or without an ethylene glycol linker, and these glycoside esters of ALA were evaluated in human cells. The results demonstrated that glycoside esters of ALA are efficient precursors of PpIX in human cancer and angiogenic endothelial cells, comparable to free ALA, but not in normal human fibroblasts. PpIX production was confirmed by fluorescence microscopy and photodynamic treatment of cells. The O-1 or O-6 positions of functionalization and the nature of the sugar moiety did not influence PpIX production. The presence of the ethylene glycol linker generally resulted in decreased PpIX production. The uptake of these glycoside esters of ALA by cells was not decreased in the presence of high concentrations of the related sugars. Inhibitors of alpha-glucosidases or alpha-mannosidases did not decrease PpIX production. These results suggest the involvement of active non-glycoside-specific membrane transporter(s) for uptake and of esterases rather than glycosidases in the release of ALA from the glycoside esters of ALA.

Synthesis of bisubstrate inhibitors of porphobilinogen synthase from Pseudomonas aeruginosa.

Porphobilinogen synthase (PBGS) synthesizes porphobilinogen 2 (PBG), the common precursor of all natural tetrapyrroles, through an asymmetric condensation of two molecules of 5-aminolevulinic acid 1 (ALA). Symmetrically linked dimers 7-11 derived from levulinic acid 3 (gamma-oxovaleric acid) have been synthesized to mimic the assumed bisubstrate bound to the active site of the enzyme. Their inhibition potential was characterized by determination of the IC(50) and K(i) values using PBGS from Pseudomonas aeruginosa. The polarity and the size of the functional group linking the two levulinic acid 3 units have a strong influence on the inhibition behavior.

A Ligand-Based NMR Screening Approach for the Identification and Characterization of Inhibitors and Promoters of Amyloid Peptide Aggregation.

Over the years a significant amount of effort has been put into the development of rapid and reliable methods to monitor the aggregation dynamics of the ß1-42 amyloid peptide in real time. We present an alternative approach based on a suitable reporter or spy molecule and three different NMR experiments: WaterLOGSY, 1 H selective T1 filter, and 19 F T2 filter, for monitoring the initial self-aggregation process kinetics of the ß1-42 amyloid peptide and identifying molecules that retard or accelerate the self-aggregation process. Although the proposed method is not a high-throughput assay, it avoids problems associated with interference events that are sometimes observed in fluorescence-based assays.

Determination of intracellular prolyl/glycyl proteases in intact living human cells and protoporphyrin IX production as a reporter system.

The determination of enzyme activity or inhibition in intact living cells is a problem in the development of inhibitors for intracellular proteases. The production of fluorescent protoporphyrin IX (PpIX) from the nonfluorescent (N)-Gly/Pro-5-aminolevulinic acid (ALA) substrates was used to evaluate the prolyl/glycyl-specific dipeptidylpeptidase IV (DPPIV)-like and prolyloligopeptidase (POP)-like activities of human cells. The results demonstrated that whereas POP-like activity could be attributed to the actual POP, the DPPIV-like activity could be related to actual DPPIV only in one colon cell line. In the other breast and colon cell lines, DPPIV-like activity was intracellular and displayed by other prolyl-specific aminopeptidases. Our experiments also demonstrated the involvement of glycyl-specific proteases in the processing of ALA precursors. These observations have important consequences for the development and evaluation of selective inhibitors for these enzymes.