Amit Shard

Stilbene–Chalcone Hybrids: Design, Synthesis, and Evaluation as a New Class of Antimalarial Scaffolds That Trigger Cell Death through Stage Specific Apoptosis

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.

Palladium‐Catalyzed Dehydrative Heck Olefination of Secondary Aryl Alcohols in Ionic Liquids: Towards a Waste‐Free Strategy for Tandem Synthesis of Stilbenoids

All in one: a tandem strategy has been developed wherein secondary aryl alcohols are directly coupled with aryl halides to provide stilbenoids through a dehydrative Heck sequence in the ionic liquid [hmim]Br, and with water as a by-product under microwave irradiation. Classical methods do not permit this sequence to proceed in one pot, and some methods require multiple steps. hmim=1-n-hexyl-3-methylimidazolium.

Pd‐Catalyzed Orthogonal Knoevenagel/Perkin Condensation–Decarboxylation–Heck/Suzuki Sequences: Tandem Transformations of Benzaldehydes into Hydroxy‐Functionalized Antidiabetic Stilbene–Cinnamoyl Hybrids and Asymmetric Distyrylbenzenes

Tandem reactions that involve chemoselective Knoevenagel/Perkin condensation-decarboxylation-Heck/Suzuki coupling or Heck-aldol sequences have been achieved. This enabled the first concise and efficient synthesis of several important hydroxy-functionalized compound classes, such as stilbene-cinnamoyl hybrids (potent protein tyrosine phosphatase1B inhibitors), cinnamoyl-cinnamic acid hybrids, asymmetric distyrylbenzenes, and biarylstyrenes. Previously reported synthesis require multiple steps and protection/deprotection manipulations.

Multicomponent Diversity-Oriented Synthesis of Symmetrical and Unsymmetrical 1,4-dihydropyridines in Recyclable Glycine Nitrate (GlyNO 3 ) Ionic Liquid: A Mechanistic Insight Using Q-TOF, ESI-MS/MS**

Multicomponent reactions are compelling strategies for generating a chemically diverse set of multifunctionalized heterocyclic motifs with high atom economy, rendering the transformations green. These strategies can further become more prolific if catalyst recyclability, compatibility and exploration of precise mechanistic pathways are considered. To this end, an inexpensive and recyclable glycine nitrate (GlyNO3) ionic liquid has been efficiently employed to obtain diversely substituted symmetrical and unsymmetrical 1,4-dihydropyridines with up to 93% yields via three and four components, respectively. The catalyst recyclability and compatibility to obtain both symmetrical and unsymmetrical 1,4 DHPs under identical reaction conditions are added benefits to its practical utility. Furthermore, progress of the reaction was monitored by Q-TOF, direct infusion electrospray ionization mass spectrometry (ESI-MS), and key cationic intermediates involved in the reaction have been further identified by a tandem MS experiment (Q-TOF, ESI-MS/MS), which served as the proof of concept to the mechanistic model. This is the first report which revealed that the Hantzsch reaction predominantly follows the diketone pathway among four competing reaction pathways.

Tandem allylic oxidation–condensation/esterification catalyzed by silica gel: an expeditious approach towards antimalarial diaryldienones and enones from natural methoxylated phenylpropenes

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.

Amino acid and water-driven tunable green protocol to access S–S/C–S bonds via aerobic oxidative coupling and hydrothiolation

A green methodology utilizing a natural supplement such as L-arginine in conjunction with water and oxygen led to oxidative coupling of thiols into disulfides (S–S bond) whereas thiol–yne coupling to access vinyl sulfides (C–S bond) was facilitated in a nitrogen atmosphere. The tunable protocol offers several advantages such as low catalyst loading, high yields, clean reaction, no over-oxidation of the S–S bond besides being metal/base/waste-free. The synthesis of ubiquitous cystine and glutathione disulfide in the same catalytic system is an added advantage and the catalytic system has been recycled up to seven times.

Establishment of a quantitative bioanalytical method for an acetylcholinesterase inhibitor Ethyl 3-(2-(4-fluorophenyl) amino)-4-phenylthiazol-5-yl)-3-oxopropanoate including its physicochemical characterization and in vitro metabolite profiling using Liquid Chromatography-Mass Spectrometry

Ethyl 3-(2-(4-fluorophenyl)amino)-4-phenylthiazo)-5-yl)-3-oxopropanoate is a novel molecule with potent acetylcholinesterase inhibition property. In this research, we have developed a rapid and selective RP-HPLC bioanalytical method for quantitative measurement of the molecule. The method has been validated following the USFDA bioanalytical method validation guideline. In addition, as a part of drug development, in vitro metabolite identification has also been performed. A Kromasil C18 column was used in eluting the molecule chromatographically. The optimized mobile phase was composed of a mixture of acetonitrile and 10 mM ammonium formate buffer (pH 4.6) in 70:30 ratio (v/v). The response of the molecule was found to be linear over a calibration range of 0.2 μg/mL to 12 μg/mL. The inter-day and intra-day accuracy of the method ranged from 89.95% to 101.90% and 99.84% to 104.08%, respectively. On the other hand, the precision (%CV) value for inter-day was in between 3.50% to 6.91% and for intra-day, it was 2.11% to 8.03%. The mean recovery of the molecule at three different quality control levels was more than 85%. The analyte was stable under different stability conditions including 12 h autosampler, 8 h bench top, 15 days long term at -20 °C and three freeze-thaw cycles. The method was applied to determine stability of the molecule in human plasma. The molecule was found to be stable with more than 90% remaining even after 120 min of incubation in plasma. Two metabolites each in rat liver microsome and human liver microsome has been identified.

Drug development and bioanalytical method validation for a novel anticancer molecule, 4-(dimethylamino)-2-(p-tolylamino) thiazole-5-carbonitrile

Hit, Lead & Candidate Discovery

Hydroxylated di- and tri-styrylbenzenes, a new class of antiplasmodial agents: discovery and mechanism of action

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.