Search

The immune system uses members of the toll-like receptor (TLR) family to recognize a variety of pathogen- and host-derived molecules in order to initiate immune responses. Although TLR-mediated, pro-inflammatory immune responses are essential for host defense, prolonged and exaggerated activation can result in inflammation pathology that manifests in a variety of diseases. Therefore, small molecule inhibitors of the TLR signaling pathway might have promise as anti-inflammatory drugs. We have previously identified a class of triaryl pyrazole compounds that inhibit TLR signaling by modulation of the protein-protein interactions essential to the pathway. We have now systematically examined the structural features essential for inhibition of this pathway, revealing characteristics of compounds that inhibited all TLRs tested (pan-TLR signaling inhibitors) as well as compounds that selectively inhibited certain TLRs. These findings reveal interesting classes of compounds that could be optimized for particular inflammatory diseases governed by different TLRs.

The first systematic evaluation of the antiplasmodial activity of the hydroxystilbene family of natural products and di/tristyrylbenzenes is described. A library of 27 diversely substituted hydroxy stilbenoids was rapidly synthesized using modified Knoevenagel–Perkin-decarboxylation–Heck sequences from readily available starting materials (i.e. hydroxybenzaldehyde–phenylacetic acid–arylhalide). These compounds were evaluated for in vitro antiplasmodial activity against three different strains of Plasmodium falciparum. Notably, 4,4′4′′-((1E,1′E,1′′E)-benzene-1,3,5-triyltris(ethene-2,1-diyl))tris(2,6-dimethoxyphenol) (27), an octupolar stilbenoid, showed IC50 (μM) values of 0.6, 0.5 and 1.36 while a distyrylbenzene (11) showed IC50 values of 0.9, 2.0 and 2.7 against 3D7 (chloroquine sensitive), Dd2 and Indo (chloroquine resistant) strains of Plasmodium falciparum respectively. Moreover, 27 and 11, which exhibited selectivity indices of 40 and >111 were also found to be nontoxic to the HeLa cell line. Microscopic studies revealed that the rings and trophozoites obtained from the 27 and 11 (an octupolar tristyrylbenzene and distyrylbenzene respectively) treated cultures were growth inhibited and morphologically deformed. These cultures also showed DNA fragmentation and loss of mitochondrial membrane potential (ΔΨm), suggestive of apoptotic death of the parasite. Together, these studies introduce di/tristyrylbenzenes as a new class of antimalarial agents.

A major risk for patients having estrogen receptor α (ERα)-positive breast cancer is the recurrence of drug-resistant metastases after initial successful treatment with endocrine therapies. Recent studies have implicated a number of activating mutations in the ligand-binding domain of ERα that stabilize the agonist conformation as a prominent mechanism for this acquired resistance. There are several critical gaps in our knowledge regarding the specific pharmacophore requirements of an antagonist that could effectively inhibit all or most of the different mutant ERs. To address this, we screened various chemotypes for blocking mutant ER-mediated transcriptional signaling and identified RU58668 as a model compound that contains structural elements that support potent ligand-induced inhibition of mutant ERs. We designed and synthesized a focused library of novel antagonists and probed how small and large perturbations in different ligand structural regions influenced inhibitory activity on individual mutant ERs in breast cancer cells. Effective inhibition derives from both non-polar and moderately polar motifs in a multifunctional side chain of the antagonists, with the nature of the ligand core making important contributions by increasing the potency of ligands possessing similar types of side chains. Some of our new antagonists potently blocked the transcriptional activity of the three most common mutant ERs (L536R, Y537S, D538G) and inhibited mutant ER-mediated cell proliferation. Supported by our molecular modeling, these studies provide new insights into the role of specific components, involving both the ligand core and multifunctional side chain, in suppressing wild-type and mutant ER-mediated transcription and breast cancer cell proliferation.

The estrogen receptors (ERs) bind with high affinity to many structurally diverse ligands by significantly distorting the contours of their ligand-binding pockets. This raises a question: To what degree is ER able to distinguish between structurally related regioisomers and enantiomers? We have explored the structural compliance and specificity of ERα with a set of ligands having a 7-oxa-bicyclo[2.2.1]hept-5-ene sulfonate core and basic side chains typical of selective ER modulators (SERMs). These ligands have two regioisomers, each of which is a racemate of enantiomers. Using orthogonal protecting groups and chiral HPLC, we isolated all 4 isomers and assigned their absolute stereochemistry by X-ray analysis. The 1S,2R,4S isomer has a 80-170-fold higher affinity for ERα than the others, and it profiles as a partial agonist/antagonist in cellular reporter gene assays and in suppressing proliferation of MCF-7 breast cancer cells with subnanomolar potency, far exceeding that of the other isomers. It is the only isomer found bound to ERα by X-ray analysis after crystallization with four-isomer mixtures of closely related analogs. Thus, despite the general compliance of this receptor for binding a large variety of ligand structures, ER demonstrates marked structural specificity and stereospecificity by selecting a single component from a mixture of structurally related isomers to drive ER-regulated cellular activity. Our findings lay the necessary groundwork for seeking unique ER-mediated pharmacological profiles by rational structural perturbations of two different types of side chains in this unprecedented class of ER ligands, which may prove useful in developing more effective endocrine therapies for breast cancer.

Novel stilbene-chalcone (S-C) hybrids were synthesized via a sequential Claisen-Schmidt-Knoevenagel-Heck approach and evaluated for antiplasmodial activity in in vitro red cell culture using SYBR Green I assay. The most potent hybrid (11) showed IC(50) of 2.2, 1.4, and 6.4 μM against 3D7 (chloroquine sensitive), Indo, and Dd2 (chloroquine resistant) strains of Plasmodium falciparum, respectively. Interestingly, the respective individual stilbene (IC(50)100 μM), chalcone (IC(50) = 11.5 μM), or an equimolar mixture of stilbene and chalcone (IC(50) = 32.5 μM) were less potent than 11. Studies done using specific stage enriched cultures and parasite in continuous culture indicate that 11 and 18 spare the schizont but block the progression of the parasite life cycle at the ring or the trophozoite stages. Further, 11 and 18 caused chromatin condensation, DNA fragmentation, and loss of mitochondrial membrane potential in Plasmodium falciparum, thereby suggesting their ability to cause apoptosis in malaria parasite.

H(2)O(2) mediated oxidation of alcohols in ionic liquid is revisited, wherein, ionic liquids under the influence of microwave irradiation have been found to facilitate activation of H(2)O(2) without any metal catalyst in aqueous condition. The method utilizes a neutral ionic liquid [hmim]Br both as catalyst and solvent for efficient and chemoselective oxidation of benzyl alcohol derivatives on aromatic (β, γ) alcohols, cyclic and aliphatic analogues, which can be a useful synthetic approach in total synthesis of complex organic compounds/natural products. Moreover, an unexpected oxidation of 9-anthracenyl propanol, a polyaromatic benzyl alcohol, resulting in the formation of 9,10-anthraquinone by the loss of propyl side chain was observed. Plausible mechanism and further exploration of this method on various other related substrates are discussed in detail.

A new approach has been developed for a one-pot and selective oxidative cleavage of aryl- and 1,2-diarylalkenes leading to one-carbon shorter aryl ketones; thereby, providing a complementary approach to classical ozonolysis. The methodology was applicable to diverse aromatic and polyaromaticarylalkenes bearing electron-donating or -withdrawing groups on the aromatic ring. The protocol also provided a useful one-pot oxidative cleavage–condensation sequence, which could potentially have important applications in natural product total synthesis.

In the present study, microwave-assisted extraction was compared with conventional approaches for the efficient extraction of juglone and other phenolics from Juglans regia bark. The effect of different solvents was also studied and ethyl acetate was found to be a better solvent in terms of juglone yield and stability. Further, a simple and fast RP-HPLC method was developed and validated for the determination of juglone and other bioactive phenolics like gallic acid, caffeic acid, quercetin, myricetin, and quercitrin in these extracts. In addition, the extracts were tested for antimicrobial activity against 16 microorganisms where all the extracts showed broad spectrum activity.

Ionic liquids have been found to provide a new platform for metal- and quinoline-free decarboxylation of various N-heteroaryl and aryl carboxylic acids under microwave irradiation in aqueous condition. The method was found to possess a wide substrate scope towards the synthesis of various pharmacologically and industrially important aromatic compounds including indoles, styrenes, stilbenes, and nitro- or hydroxyarene derivatives. The decarboxylation of indole and alpha-phenylcinnamic acids proceeded well without addition of any catalyst in neat 1-hexyl-3-methylimidazolium bromide ([hmim]Br) and 1-methylimidazolium p-toluenesulfonic acid ([Hmim]PTSA), respectively, while addition of a mild base like aqueous sodium hydrogen carbonate (NaHCO(3)) to [hmim]Br further improved the decarboxylation of hydroxylated cinnamic and aromatic acid substrates. The developed methodology not only precludes the usage of toxic metal/quinoline and harsh organic bases but also offers several inherent benefits like recyclability of reagent system, reduction in waste and hazards, short reaction time besides ease of product recovery.

A mild and efficient, ionic-liquid-assisted, green protocol for the dehydration of benzyl alcohols into the corresponding (E)-arylalkenes under microwave irradiation has been developed. The method utilizes a neutral and recyclable ionic liquid (1-hexyl-3-methylimidazolium bromide) as a reagent and solvent to cleanly provide a wide range of olefins withoutthe need of harsh and expensive Bronsted/Lewis acids. The method was extended to the efficient conversion of acetylated/ benzoylated derivatives of benzyl alcohol into their corresponding (E)-arylalkenes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Shikonin and its derivatives are important red colored naphthoquinone pigments found in a large number of Arnebia species, including A. euchroma, that are responsible for the various pharmacological activities exhibited by the plant. The precise separation of each naphthoquinone is essential for total quality evaluation and bioactivity analysis of herbal formulations of A. euchroma. Furthermore, the overexploitation of this useful plant has resulted in species becoming endangered. With this in mind, a simple and rapid preparative scale HPLC method with single compound recovery for the isolation and purification of two shikonin derivatives (i. e. acetylshikonin, beta-acetoxyisovalerylshikonin) from cell suspension cultures of A. euchroma is presented. The compounds were separated on a C(18) column within 10 min using acetonitrile/methanol (95:5) as mobile phase in isocratic mode. The isolated compounds were found to be more than 98% pure. The LOD for acetylshikonin and beta-acetoxyisovalerylshikonin was estimated at 0.063 and 0.146 mug/mL, respectively, while the LOQ was found to be 0.209 and 0.487 mug/mL, respectively. The recoveries accomplished for both the shikonin derivatives were in the range of 94.7-96.8%. The repeatability, expressed as %RSD, of acetylshikonin and beta-acetoxyisovalerylshikonin was found to be 1.74 and 1.27, respectively.

A sequential Heck reaction of acrylic acid with aromatic halides followed by decarboxylation and a second Heck reaction is developed.

A variety of important hydroxy-functionalized classes of compounds is prepared under microwave-assisted conditions.

H(2)O(2) mediated oxidation of alcohols in ionic liquid is revisited, wherein, ionic liquids under the influence of microwave irradiation have been found to facilitate activation of H(2)O(2) without any metal catalyst in aqueous condition. The method utilizes a neutral ionic liquid [hmim]Br both as catalyst and solvent for efficient and chemoselective oxidation of benzyl alcohol derivatives on aromatic (β, γ) alcohols, cyclic and aliphatic analogues, which can be a useful synthetic approach in total synthesis of complex organic compounds/natural products. Moreover, an unexpected oxidation of 9-anthracenyl propanol, a polyaromatic benzyl alcohol, resulting in the formation of 9,10-anthraquinone by the loss of propyl side chain was observed. Plausible mechanism and further exploration of this method on various other related substrates are discussed in detail.

Allylic oxidation of styrene derivatives (I) and (IV) with DDQ provides the corresponding cinnamaldehyde intermediates which subsequently undergo SOCl2-mediated condensation with acetophenone derivatives (II) and (V) to give dienones (III) and (VI), respectively.

The title reaction is applicable to diverse aromatic and polyaromatic arylalkenes bearing electron-donating or -withdrawing groups on the aromatic ring.

A series of 2- or 4-hydroxy substituted benzaldehydes is converted into stilbene derivatives by a Knoevenagel-decarboxylation-Heck sequence.

A new approach for one step olefination of benzaldehydes into hydroxy functionalized OPVs is achieved through the first domino Knoevenagel-decarboxylation-Heck sequence using a single catalyst system. The methodology also led to new oxygen based OPV scaffolds capable of selective and visible fluoride recognition in organic or aqueous medium.

A number of green methodologies employing microwave, ionic liquids, ultrasound, etc have been developed for the synthesis and isolation of diverse bioactive phenolics. The use of above green tools greatly improve the reaction performance and provides additional benefits like reduction in cost and waste besides replacement of hazardous chemicals.

The direct oxidation of arylalkenes into α-arylaldehydes is achieved for the first time in water without relying on transition metal catalysts, and a novel organocatalytic enantioselective approach is also explored to provide up to 30% ee in initial investigations.

The direct oxidation of arylalkenes into alpha-arylaldehydes is achieved for the first time in water without relying on transition metal catalysts, and a novel organocatalytic enantioselective approach is also explored to provide up to 30% ee in initial investigations.

Ionic liquids have been found to provide a new platform for metal- and quinoline-free decarboxylation of various N-heteroaryl and aryl carboxylic acids under microwave irradiation in aqueous condition. The method was found to possess a wide substrate scope towards the synthesis of various pharmacologically and industrially important aromatic compounds including indoles, styrenes, stilbenes, and nitro- or hydroxyarene derivatives. The decarboxylation of indole and alpha-phenylcinnamic acids proceeded well without addition of any catalyst in neat 1-hexyl-3-methylimidazolium bromide ([hmim]Br) and 1-methylimidazolium p-toluenesulfonic acid ([Hmim]PTSA), respectively, while addition of a mild base like aqueous sodium hydrogen carbonate (NaHCO(3)) to [hmim]Br further improved the decarboxylation of hydroxylated cinnamic and aromatic acid substrates. The developed methodology not only precludes the usage of toxic metal/quinoline and harsh organic bases but also offers several inherent benefits like recyclability of reagent system, reduction in waste and hazards, short reaction time besides ease of product recovery.

A mild and efficient, ionic-liquid-assisted, green protocol for the dehydration of benzyl alcohols into the corresponding (E)-arylalkenes under microwave irradiation has been developed. The method utilizes a neutral and recyclable ionic liquid (1-hexyl-3-methylimidazolium bromide) as a reagent and solvent to cleanly provide a wide range of olefins withoutthe need of harsh and expensive Bronsted/Lewis acids. The method was extended to the efficient conversion of acetylated/ benzoylated derivatives of benzyl alcohol into their corresponding (E)-arylalkenes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A new one-pot strategy has been developed, wherein abundantly available methoxylated phenylpropenes are directly transformed into corresponding dienones (1,5-diarylpenta-2,4-dien-1-ones) and enones (chalcones and cinnamic esters) via allylic oxidation-condensation or allylic oxidation-esterification sequences. Preliminary antimalarial activity studies of the above synthesized diaryldienones and enones against Plasmodium falciparum (Pf3D7) have shown them to be promising lead candidates for developing newer and economical antimalarial agents. In particular, two enones (12b and 13b) were found to possess comparatively better activity (IC(50) = 4.0 and 3.4 μM, respectively) than licochalcone (IC(50) = 4.1 μM), a well known natural antimalarial compound.