Synthesis and molecular structure of 3-(2-benzyloxy-6-hydroxyphenyl)-5-styrylpyrazoles. Reaction of 2-styrylchromones and hydrazine hydrate

Styrylpyrazoles: Properties, Synthesis and Transformations

The pyrazole nucleus and its reduced forms, pyrazolines and pyrazolidine, are privileged scaffolds in medicinal chemistry due to their remarkable biological activities. A huge number of pyrazole derivatives have been studied and reported over time. This review article gives an overview of pyrazole derivatives that contain a styryl (2-arylvinyl) group linked in different positions of the pyrazole backbone. Although there are studies on the synthesis of styrylpyrazoles dating back to the 1970s and even earlier, this type of compound has rarely been studied. This timely review intends to summarize the properties, biological activity, methods of synthesis and transformation of styrylpyrazoles; thus, highlighting the interest and huge potential for application of this kind of compound.

Crystal structure of 4-bromo-2-(1H-pyrazol-3-yl)phenol, C9H7BrN2O

C9H7BrN2O, triclinic, C2/c (no. 15), a = 16.255(3) Å, b = 4.4119(9) Å, c = 25.923(5) Å, β = 107.99(3)°, V = 1768.2(7) Å3, Z = 8, R gt(F) = 0.0450, wR ref(F 2) = 0.0960, T = 150 K.

Quantitative Structure-Antifungal Activity Relationships for cinnamate derivatives

Quantitative Structure-Activity Relationships (QSAR) are established with the aim of analyzing the fungicidal activities of a set of 27 active cinnamate derivatives. The exploration of more than a thousand of constitutional, topological, geometrical and electronic molecular descriptors, which are calculated with Dragon software, leads to predictions of the growth inhibition on Pythium sp and Corticium rolfsii fungi species, in close agreement to the experimental values extracted from the literature. A set containing 21 new structurally related cinnamate compounds is prepared. The developed QSAR models are applied to predict the unknown fungicidal activity of this set, showing that cinnamates like 38, 28 and 42 are expected to be highly active for Pythium sp, while this is also predicted for 28 and 34 in C. rolfsii.

Characterisation of (E)-2-styrylchromones by electrospray ionisation mass spectrometry: singular gas-phase formation of benzoxanthenones

RATIONALE

The electrospray ionisation (ESI) mass spectra (ESI-MS(n) , n = 2 and 3) of six (E)-2-styrylchromones containing electron-donating and electron-withdrawing groups were studied for the first time. The potential application of these compounds as drug candidates brings a need for the development of an analytical method to ensure a detailed knowledge of their structures.

METHODS

ESI-MS, CID-MS(2) and MS(3) spectra of all the studied compounds were acquired using a LXQ linear ion trap mass spectrometer with an electrospray source, operating in the positive ion mode. ESI conditions were: nitrogen 8.00 sheath gas flow rate (arb), spray voltage 5 kV, heated capillary temperature 275 °C, capillary voltage 10.99 V and tube lens voltage 75.01 V. CID-MS(2) and MS(3) experiments were performed on mass-selected precursor ions using standard isolation and excitation procedures (activation q value of 0.25, activation time of 30 ms).

RESULTS

A comparable pattern of product ions was observed for all the studied compounds. Only the product ion ((1,2)(3,4)) A(+) is common to all the studied compounds. Common to compounds 1 (R(2) = H), 1a (R(2) = OMe) and 1c (R(2) = Cl) are the product ions formed by loss of H(2)O, CO, C(6)H(5)OH, and the product ions ((1,2)(2,3))B(+) and ((1,2)(3,4))B(+). Among all compounds, 2-SC 1b (R(2) = NO(2)) shows an obvious differentiation showing the lowest number of product ions under CID-MS(2) conditions.

CONCLUSIONS

The analysed compounds revealed a comparable pattern of product ions formed for each compound only different in what concerns the relative abundance of these formed product ions. A rather interesting and unexpected loss of 2 Da was observed for some compounds. The structure of a benzoxanthenone was proposed for this product ion based on evidence obtained by synthesised benzoxanthenone as a model compound.

Chemically engineered extracts: source of bioactive compounds

Biological research and drug discovery critically depend on access to libraries of small molecules that have an affinity for biomacromolecules. By virtue of their sustained success as sources of lead compounds, natural products are recognized as "privileged" starting points in structural space for library development. Compared with synthetic compounds, natural products have distinguishing structural properties; indeed, researchers have begun to quantify and catalog the differences between the two classes of molecules. Measurable differences in the number of chiral centers, the degree of saturation, the presence of aromatic rings, and the number of the various heteroatoms are among the chief distinctions between natural and synthetic compounds. Natural products also include a significant proportion of recurring molecular scaffolds that are not present in currently marketed drugs: the bioactivity of these natural substructures has been refined over the long process of evolution. In this Account, we present our research aimed at preparing libraries of semisynthetic compounds, or chemically engineered extracts (CEEs), through chemical diversification of natural products mixtures. The approach relies on the power of numbers, that is, in the chemical alteration of a sizable fraction of the starting complex mixture. Major changes in composition can be achieved through the chemical transformation of reactive molecular fragments that are found in most natural products. If such fragments are common enough, their transformation represents an entry point for chemically altering a high proportion of the components of crude natural extracts. We have searched for common reactive fragments in the Dictionary of Natural Products (CRC Press) and identified several functional groups that are expected to be present in a large fraction of the components of an average natural crude extract. To date, we have used reactions that incorporate (i) nitrogen atoms through carbonyl groups, (ii) sulfur by transformation of -OH and amines, and (iii) bromine through double bonds and aromatic rings. The resulting CEEs had different composition and biomolecular properties than their natural progenitors. We isolated a semisynthetic β-glucosidase inhibitor from a CEE prepared by reaction with benzenesulfonyl chloride, an antifungal pyrazole from a CEE prepared by reaction with hydrazine, and an acetylcholinesterase inhibitor from a CEE prepared through bromination. Our results illustrate how biological activity can be generated through chemical diversification of natural product mixtures. Moreover, the level of control that can be asserted in the process by judicious design and experimental choices underscores the potential for further development of CEEs in both basic research and drug discovery.

Cytotoxic effect, differentiation, inhibition of growth and theoretical calculations of an N,N-donor ligands and its platinum(II), palladium(II) and copper(II) complexes

The new pyrazole ligand 5-(2-hydroxyphenyl)-3-methyl-1-(2-pyridylo)-1H-pyrazole-4-carboxylic acid methyl ester (2) and the corresponding Pt(II), Pd(II) and Cu(II) complexes 3-5 have been synthesized as potential anticancer compounds, and characterized using IR, and (1)H NMR as well as mass spectrometry. The 3-D structures of the Cu(II) complexes were determined by quantum mechanic calculation DFT methodology (density functional theory). The cytotoxicity assay of the ligand and complexes has been performed on leukemia cell lines. In general, the complexes showed lower cytotoxicity than cisplatin, and the Pt(II) and Cu(II) complexes were found to be more efficient in the induction of leukemia cell death than the Pd(II) complex. Our investigations indicate that the antiproliferating activity of the Pt(II) and Cu(II) complexes was partly due to the modulation of cellular differentiation.

Chemically engineered extracts as an alternative source of bioactive natural product-like compounds

The access to libraries of molecules with interesting biomolecular properties is a limiting step in the drug discovery process. By virtue of a long molecular evolution process, natural products are recognized as biologically validated starting points in structural space for library development. We introduce here a strategy to generate natural product-like libraries. A semisynthetic mixture of compounds was produced by diversification of a natural product extract through the chemical transformation of common chemical functionalities in natural products into chemical functionalities rarely found in nature. The resulting mixture showed antifungal activity against Candida albicans, whereas the starting extract did not show such activity. Bioguided fractionation led to the isolation of a previously undescribed active semisynthetic pyrazole. The result illustrates how biological activity can be generated by designed chemical diversification of a natural product mixture, and represents the proof of principle of an alternative strategy for producing natural product-like libraries from natural products libraries.

Synthesis of 4-Aryl-3(5)-(2-hydroxyphenyl)pyrazoles by Reaction of Isoflavones and their 4-Thio Analogues with Hydrazine Derivatives

4-Aryl-3(5)-2-(hydroxyphenyl)pyrazoles have been prepared by the reaction of isoflavones and their 4-thio analogues with hydrazine hydrate and phenylhydrazine in hot pyridine. The reaction mechanism for the formation of these pyrazoles is discussed. All the new compounds have been fully characterized by NMR spectroscopy. In [D6]DMSO, a 1H NMR study allows observation of the presence of both pyrazole annular tautomers, due to the presence of intramolecular hydrogen bonds in each tautomer (OH···N and NH···O). Theoretical calculations have been carried out on tautomers and conformers of compounds 20 (3(5)-(2-hydroxy-4-methoxyphenyl)-5(3)-methyl-4-phenylpyrazole) and 21 (3(5)-(2-hydroxy-4-methoxyphenyl)-4-(2-methoxyphenyl)-5(3)-methylpyrazole), including the absolute shieldings (GIAO/B3 LYP/6–311++G**) of 21.

Synthesis and anti-rhinovirus activity of 2-styrylchromones

2-Styrylchromones were synthesized as vinylogues of 2-phenylchromones (flavones), a broad class of anti-rhinovirus compounds. The antiviral activity of 2-styrylchromones and 3-hydroxy-1-(2-hydroxyphenyl)-5-phenyl-2,4-pentadien-1-ones, which are intermediates in the synthesis, was evaluated against two selected serotypes of human rhinovirus, 1B and 14, by a plaque reduction assay in HeLa cell cultures. All of the compounds interfered with HRV 1B replication, with the exception of 3-hydroxy-1-(2-hydroxyphenyl)-5-(4-methoxyphenyl)-2,4-pentadien-1-one. The majority of derivatives were also found to be effective against serotype 14, often with a higher potency.