Linked parallel synthesis and MTT bioassay screening of substituted chalcones

Molecular interactions at the colchicine binding site in tubulin: An X-ray crystallography perspective

Tubulin is an important cancer drug target. Compounds that bind at the colchicine site in tubulin have attracted significant interest as they are generally less affected by multidrug resistance than other potential drugs. Modeling is useful in understanding the interactions between tubulin and colchicine binding site inhibitors (CBSIs), but because the colchicine binding site contains two flexible loops whose conformations are highly ligand-dependent, modeling has its limitations. X-ray crystallography provides experimental pictures of tubulin-ligand interactions at this challenging colchicine site. Since 2004, when the first X-ray structure of tubulin in complex with N-deacetyl-N-(2-mercaptoacetyl)-colchicine (DAMA-colchicine) was published, many X-ray crystal structures have been reported for tubulin complexes involving the colchicine binding site. In this review, we summarize the crystal structures of tubulin in complexes with various CBSIs, aiming to facilitate the discovery of new generations of tubulin inhibitors.

Antitumour, acute toxicity and molecular modeling studies of 4-(pyridin-4-yl)-6-(thiophen-2-yl) pyrimidin-2(1H)-one against Ehrlich ascites carcinoma and sarcoma-180

In an effort to discover an effective and selective antitumour agent, synthesis and anti-cancer potential of 4-(pyridin-4-yl)-6-(thiophen-2-yl) pyrimidin-2(1H)-one (SK-25), which has been reported earlier by us with significant cytotoxicity towards MiaPaCa-2 malignant cells, with an IC₅₀ value of 1.95 μM and was found to instigate apoptosis. In the present study, the antitumour efficacy of SK-25 was investigated on Ehrlich ascites tumour (EAT, solid), Sarcoma 180 (solid) tumour and Ehrlich ascites carcinoma. The compound was found to inhibit tumour development by 94.71% in Ehrlich ascites carcinoma (EAC), 59.06% in Ehrlich tumour (ET, solid) and 45.68% in Sarcoma-180 (solid) at 30 mg/kg dose. Additionally, SK-25 was established to be non-toxic at a maximum tolerated dose of 1000 mg/kg in acute oral toxicity in Swiss-albino mice. Computer-based predictions also show that the compounds could have an interesting DMPK profile since all 51 computed physicochemical parameters fall within the recommended range for 95% of known drugs. The current study provides insight for further investigation of the antitumour potential of the molecule.

Novel Natural Product- and Privileged Scaffold-Based Tubulin Inhibitors Targeting the Colchicine Binding Site

Tubulin inhibitors are effective anticancer agents, however, there are many limitations to the use of available tubulin inhibitors in the clinic, such as multidrug resistance, severe side-effects, and generally poor bioavailability. Thus, there is a constant need to search for novel tubulin inhibitors that can overcome these limitations. Natural product and privileged structures targeting tubulin have promoted the discovery and optimization of tubulin inhibitors. This review will focus on novel tubulin inhibitors derived from natural products and privileged structures targeting the colchicine binding site on tubulin.

Concise Total Synthesis of 1,3-Diphenylpropane Derivatives Griffithanes A, B and F

Concise and efficient total syntheses of diarylpropanes griffithane A, B and F, isolated from Combretum griffithii, have been accomplished from methoxybenzaldehyde. The Claisen–Schmidt condensation between aldehyde and acetophenone was applied to form chalcone as a key step. The structures of chalcones are confirmed by crystal X-ray crystallography.

Synthesis, DNA binding, docking and photocleavage studies of quinolinyl chalcones

A series of simple quinoline–chalcone conjugates have been synthesized and evaluated for their nucleolytic activity. The compounds 3c and 3d exhibited promising DNA binding and DNA photocleavage studies.

Design, synthesis and cytotoxicity of novel chalcone analogs derived from 1-cyclohexylpyrrolidin-2-one and 2,3-dihydrobenzo[f]chromen-1-one

Two divergent series of novel chalcone analogs, one derived from 1-cyclohexylpyrrolidin-2-one and the other derived from 1-benzo[f]chromanone, were designed, synthesized and evaluated for cytotoxicity against two murine cancer cell lines. Two 1-benzo[f]chromanone analogs, 4g and 4j yielded moderate toxicity against both melanoma B16 and lymphoma L1210 cell lines with IC(50) values between the range of 5 and 6 µM. With an IC(50) value of 3.4 µM, compound 4g was also active against human MDA-MB-435 melanoma cells. X-ray structures of the β-hydroxy ketone product (4a) and the α,β-unsaturated ketone (4h) were collected, and confirm the syn-configuration between the carbonyl moiety and the β-vinylic proton in 4h. X-ray structures of two 1-cyclohexylpyrrolidin-2-one derivatives were also obtained, and both showed an E-configuration for the double bond.

(2E,4E)-1-(2-Hy-droxy-phen-yl)-5-phenyl-penta-2,4-dien-1-one

In the structure of the title chalcone, C₁₇H₁₄O₂, derived from cinnamaldehyde, the olefine group has a trans configuration. The mol­ecular conformation is stabilized by an intra­molecular O—H⋯O hydrogen-bond inter­action with graph-set motif S(6).

Microwave assisted solvent free synthesis of 1,3-diphenylpropenones

BACKGROUND

1,3-Diphenylpropenones (chalcones) are well known for their diverse array of bioactivities. Hydroxyl group substituted chalcones are the main precursor in the synthesis of flavonoids. Till date various methods have been developed for the synthesis of these very interesting molecules. Continuing our efforts for the development of simple, eco-friendly and cost-effective methodologies, we report here a solvent free condensation of aryl ketones and aldehydes using iodine impregnated alumina under microwave activation. This new protocol has been applied to a variety of substituted aryl carbonyls with excellent yield of substituted 1,3-diphenylpropenones.

RESULTS

Differently substituted chalcones were synthesized using iodine impregnated neutral alumina as catalyst in 79-95% yield in less than 2 minutes time under microwave activation without using any solvent. The reaction was studied under different catalytic conditions and it was found that molecular iodine supported over neutral alumina gives the best yield. The otherwise difficult single step condensation of hydroxy substituted aryl carbonyls is an attractive feature of this protocol to obtain polyhydroxychalcones in excellent yields. In order to find out the general applicability of this new endeavor it was successfully applied for the synthesis of 15 different chalcones including highly bioactive prenylated hydroxychalcone xanthohumol.

CONCLUSION

A new, simple and solvent free method was developed for the synthesis of substituted chalcones in environmentally benign way. The mild reaction conditions, easy work-up, clean reaction profiles render this approach as an interesting alternative to the existing methods.

Dietary chalcones with chemopreventive and chemotherapeutic potential

Chalcones are absorbed in the daily diet and appear to be promising cancer chemopreventive agents. Chalcones represent an important group of the polyphenolic family, which includes a large number of naturally occurring molecules. This family possesses an interesting spectrum of biological activities, including antioxidative, antibacterial, anti-inflammatory, anticancer, cytotoxic, and immunosuppressive potential. Compounds of this family have been shown to interfere with each step of carcinogenesis, including initiation, promotion and progression. Moreover, numerous compounds from the family of dietary chalcones appear to show activity against cancer cells, suggesting that these molecules or their derivatives may be considered as potential anticancer drugs. This review will focus primarily on prominent members of the chalcone family with an 1,3-diphenyl-2-propenon core structure. Specifically, the inhibitory effects of these compounds on the different steps of carcinogenesis that reveal interesting chemopreventive and chemotherapeutic potential will be discussed.

(E)-1-[4-(Prop-2-yn-1-yl-oxy)phen-yl]-3-(3,4,5-trimeth-oxy-phen-yl)prop-2-en-1-one

The mol­ecule of the title chalcone derivative, C₂₁H₂₀O₅, consists of two substituted aromatic rings bridged by a prop-2-en-1-one group. The dihedral angle between the two benzene rings is 28.7 (7)°. In the crystal, mol­ecules are linked into C(10) chains running along the a axis by inter­molecular C—H⋯O hydrogen bonds, and the chains are cross-linked via C—H⋯π inter­actions.

(E)-3-(2,6-Dichloro-phen-yl)-1-(4-methoxy-phen-yl)prop-2-en-1-one

In the title compound, C(16)H(12)Cl(2)O(2), the dichloro-phenyl and methoxy-phenyl groups are linked by a prop-2-en-1-one group. The C=C double bond is trans configured. The mol-ecule is not planar, as can be seen from the dihedral angle of 6.21 (7)° between the planes of the two rings. The crystal structure can be described by two types of crossed layers which are parallel to (110) and (10).

Isolation and synthesis of a new chromenochalcone and a new chromene from Orthosiphon glabratus

Chemical investigation on Orthosiphon glabratus afforded 10 compounds, among which a chromenochalcone and a chromene are new. The structures of the new constituents were settled from their 1D- and 2D-NMR spectra. The synthesis of these two compounds and some of their analogues have been accomplished.

(E)-3-(3-Bromo-phen-yl)-1-(4-methyl-phenyl)prop-2-en-1-one

The title compound, C₁₆H₁₃BrO, was synthesized from the reaction of 3-bromo­benzaldehyde and 4-methyl­acetophenone in the presence of KOH. The mol­ecule adopts an E configuration with respect to the C=C double bond of the propenone unit. The dihedral angle formed by the aromatic rings is 46.91 (14)°. The crystal structure is stabilized by Br⋯Br inter­actions [3.4549 (11) Å].

Design, synthesis, and biological testing of pyrazoline derivatives of combretastatin-A4

Fourteen N-acetylated and non-acetylated 3,4,5-tri- or 2,5-dimethoxypyrazoline analogs of combretastatin-A4 (1) were synthesized. A non-acetylated derivative (5a) with the same substituents as CA-4 (1) was the most active compound in the series, with IC(50) values of 2.1 and 0.5 microM in B16 and L1210 cell lines, respectively. In contrast, a similar compound with an acetyl group at N1 of the pyrazoline ring (6g) showed poor activity in the cell lines studied. A cell-based assay indicated that compound 5a caused extensive microtubule depolymerization with an EC(50) value of 7.1 microM in A-10 cells while no activity was seen with the acetylated compound. Molecular modeling studies showed that these compounds possess a twisted conformation similar to CA-4 (1).

CYP2C9 Structure−Metabolism Relationships: Optimizing the Metabolic Stability of COX-2 Inhibitors

The cytochrome P450 (CYP) family is composed of a large group of monooxygenases that mediate the metabolism of xenobiotics and endogenous compounds. CYP2C9, one of the major isoforms of the CYP family, is responsible for the phase I metabolism of a variety of drugs. The aim of the present investigation is to use rational design together with MetaSite, a metabolism site prediction program, to synthesize compounds that retain their pharmacological effects but that are metabolically more stable in the presence of CYP2C9. The model compound for the study is the nonsteroidal anti-inflammatory drug celecoxib, a COX-2 selective inhibitor and known CYP2C9 substrate. Thirteen analogs of celecoxib were designed, synthesized, and evaluated with regard to their metabolic properties and pharmacologic effects. The docking solutions and the predictions from MetaSite gave useful information leading to the design of new compounds with improved metabolic properties.

Mining the NCI antiviral compounds for HIV-1 integrase inhibitors

HIV-1 integrase (IN) is an essential enzyme for effective viral replication and is a validated target for the development of antiretroviral drugs. Currently, there are no approved drugs targeting this enzyme. In this study, we have identified 11 structurally diverse small-molecule inhibitors of IN. These compounds have been selected by mining the moderately active antiviral molecules from a collection of 90,000 compounds screened by the National Cancer Institute (NCI) Antiviral Program. These compounds, which were screened at the NCI during the past 20 years, resulted in approximately 4000 compounds labeled as 'moderately active.' In our study, chalcone 11 shows the most potent activity with an IC(50) of 2+/-1 microM against purified IN in the presence of both Mn(2+) and Mg(2+) as cofactors. Docking simulations using the 11 identified inhibitors as a training set have elucidated two unique binding areas within the active site: the first encompasses the conserved D64-D116-E152 motif, while the other involves the flexible loop region formed by amino acid residues 140-149. The tested inhibitors exhibit favorable interactions with important amino acid residues through van der Waals and H-bonding contacts.

Combinatorial Synthesis and Antibacterial Evaluation of an Indexed Chalcone Library

A 120-membered chalcone library has been designed and prepared from six differently substituted acetophenones (A1-A6) and 20 benzaldehydes (B1-B20). The library was subjected to biological studies targeted against six bacterial strains. For the identification of the most-active member(s) of the library, the so-called indexed or positional-scanning method was applied. Six out of 26 sub-libraries, i.e., AL1-AL6, were synthesized by keeping the acetophenone moiety A fixed and using equimolar quantities of the 20 different benzaldehydes. The remaining 20 sub-libraries BL1-BL20 were prepared by keeping the benzaldehyde B component fixed and varying the six acetophenones (Table 1). The bactericidal activities of the resulting sub-libraries were tested and used as indices to the rows or columns of a two-dimensional matrix. Finally, parallel synthesis of 24 specific members with the highest-expected antibacterial activities, present in two sub-libraries, was carried out. These chalcones were screened again, and the results were exploited for establishing the structure-activity relationship (SAR) and the identification of the lead compound, which turned out to be 1,3-bis(2-hydroxyphenyl)prop-2-en-1-one (A2B2) in terms of activity towards Staphylococcus aureus and Bacillus subtilis (Tables 5-7).

Synthesis and cytotoxicity of epoxide and pyrazole analogs of the combretastatins

Twenty-six epoxide and corresponding pyrazole derivatives, of the structurally related chalcones and combretastatin A-4 (CA-4), were synthesized and tested for in vitro cytotoxicity. These molecules were synthesized by epoxidation of the relevant chalcones, followed by reaction with hydrazine. The structures of epoxides 3 and 7, and pyrazole 17, were confirmed by X-ray diffraction studies. The relatively coplanar conformation of a 3',3'',4',4'',5',5''-hexamethoxypyrazole 17 was in good agreement with the shape for 3',3'',4',4'',5'-pentamethoxypyrazole 16, which was determined from molecular mechanics optimization. In vitro cytotoxicity of each class of compounds was obtained using a 72 h continuous exposure MTT assay against two murine cancer cell lines; B16 melanoma and L1210 leukemia. The effect of substitution in the A-ring is addressed: three methoxy groups versus two, generally increased cytotoxicity across both cell lines. In the majority of cases, the pyrazoles are generally more active than the epoxides, with the most active, 5-(3''-amino-4''-methoxyphenyl)-3-(3',4',5'-trimethoxyphenyl)pyrazole 21, possessing an IC(50) value of 5 and 2.4 microM (B16 and L1210, respectively). Due to their planar conformations, the pyrazoles are typically less active than the corresponding chalcones, which adopt angular conformations similar to CA-4. B-ring modifications confirmed that in general the amino compounds are more active than the corresponding nitro compounds. Varying the number and orientation of methoxy groups on the A-ring did not produce any significant differences in toxicity in the cell lines studied.

Synthesis and evaluation of double bond substituted combretastatins

A series of combretastatins substituted with epoxides, amides and small alkyl groups has been synthesised and evaluated for cytotoxicity and their ability to inhibit the assembly of tubulin. The methyl and ethyl substituted phenols 36, 44 have shown potent antimitotic effects whilst exhibiting reduced cytotoxicity.

Quantitative Structure−Activity Relationship (5D-QSAR) Study of Combretastatin-like Analogues as Inhibitors of Tubulin Assembly

A molecular modeling study was carried out to develop a predictive model for combretastatin-like analogues populating the colchicine-binding site of beta-tubulin. A series of compounds built around a framework including two aromatic groups linked by various moieties such as alkenes (stilbenes), enones (chalcones), or ethers was selected for the study. The 5D-QSAR model was developed stepwise. First a model was generated for the chalcone series (19 compounds, 71 conformations), then for the stilbene series (18 compounds, 59 conformations), and finally for the combined dataset (47 ligands, 160 conformers). Although the models for the chalcone and stilbene series appeared slightly different when represented by QSAR colored surfaces, the combined model seems to reconcile the differences without compromise and represents a highly predictive model for compounds that bind to the colchicine-binding site of tubulin.

Microwave-Accelerated SPOT-Synthesis on Cellulose Supports

[reaction: see text] We demonstrate that microwave irradiation can dramatically accelerate reaction rates for spatially addressable library synthesis on planar membrane supports. The development of a robust support/linker system, microwave-assisted synthesis of small molecule test libraries, and methods for solid-phase scale-up on cellulose are described.

Automated parallel solid-phase synthesis and anticancer screening of a library of peptide-tethered platinum(II) complexes

The automated parallel solid-phase synthesis of a 36-member library of peptide-tethered platinum(II) complexes is described. The identity and quality of each product were confirmed by mass spectrometry and (1)H NMR. Subsequently, each compound was screened for in vitro anticancer activity by treating the A2780 (human ovarian carcinoma) cell line with two concentrations of the drugs (100 and 10 microM) in quadruplicate. The reduction of cell proliferation induced by the drugs at these concentrations was determined with the MTT colorimetric assay (MTT = 3-(4',5'-dimethylthiazol-2'-yl)-2,5-diphenyltetrazolium bromide) and compared to cisplatin. Even though no very active library members could be identified, five apparently most active (8[1], 8[4], 8[10], 8[13], and 8[24]) and two inactive complexes (8[33] and 8[34]) were purified using gel permeation chromatography and fully characterized by NMR spectroscopy ((1)H, (195)Pt) and MS. The IC(50) values of these complexes and cisplatin in A2780 cells were subsequently determined using the MTT assay in a conventional manner. All seven complexes have an IC(50) above 100 microM, confirming the results generated by the assay at 100 and 10 microM of the crude reaction products.

Pyrimidoquinazoline-based antitumor agents. Design of topoisomerase II to DNA cross-linkers with activity against protein kinases

A series of pyrimidoquinazoline analogues, possessing either 4,5-g or 5,4-g fusion, were studied with respect to cytotoxicity, topoisomerase II inhibitory activity, in vivo activity, and DNA cleavage and DNA-protein cross-linking properties. These analogues were designed as electron-deficient anthraquinones with dual alkylating centers to cross-link DNA with topoisomerase II. Our studies verified the presence of DNA-protein cross-linking in vitro as well as topoisomerase II poisoning by pyrimidoquinazoline analogues. In addition, COMPARE analysis revealed that the pyrimidoquinazolines possess inhibitory activity against both topoisomerase II and protein kinases, such as the paullones, a dual property observed in other antineoplastic agents influencing phosphoester transfer.