Prathama S. Mainkar

Phenyl 1,2,3-Triazole-Thymidine Ligands Stabilize G-Quadruplex DNA, Inhibit DNA Synthesis and Potentially Reduce Tumor Cell Proliferation over 3′-Azido Deoxythymidine

Triazoles are known for their non-toxicity, higher stability and therapeutic activity. Few nucleoside (L1, L2 and L3) and non-nucleoside 1,2,3-triazoles (L4–L14) were synthesised using click chemistry and they were screened for tumor cell cytotoxicity and proliferation. Among these triazole ligands studied, nucleoside ligands exhibited higher potential than non-nucleoside ligands. The nucleoside triazole analogues, 3′-Phenyl-1,2,3- triazole-thymidine (L2) and 3′-4-Chlorophenyl-1,2,3-triazole-thymidine (L3), demonstrated higher cytotoxicity in tumor cells than in normal cells. The IC50 value for L3 was lowest (50 µM) among the ligands studied. L3 terminated cell cycle at S, G2/M phases and enhanced sub-G1 populations, manifesting induction of apoptosis in tumor cells. Confocal studies indicated that nucleoside triazole ligands (L2/L3) cause higher DNA fragmentation than other ligands. Preclinical experiments with tumor-induced mice showed greater reduction in tumor size with L3. In vitro DNA synthesis reaction with L3 exhibited higher DNA synthesis inhibition with quadruplex forming DNA (QF DNA) than non quadruplex forming DNA (NQF DNA). Tm of quadruplex DNA increased in the presence of L3, indicating its ability to enhance stability of quadruplex DNA at elevated temperature and the results indicate that it had higher affinity towards quadruplex DNA than the other forms of DNA (like dsDNA and ssDNA). From western blot experiment, it was noticed that telomerase expression levels in the tissues of tumor-induced mice were found to be reduced on L3 treatment. Microcalorimetry results emphasise that two nucleoside triazole ligands (L2/L3) interact with quadruplex DNA with significantly higher affinity (Kd≈10−7 M). Interestingly the addition of an electronegative moiety to the phenyl group of L2 enhanced its anti-proliferative activity. Though IC50 values are not significantly low with L3, the studies on series of synthetic 1,2,3-triazole ligands are useful for improving and building potential pro-apoptotic ligands.

Peptidomimetic organocatalysts: efficient Michael addition of ketones onto nitroolefins with very low catalyst loading

The syntheses of two novel peptidomimetic triazole-based organocatalysts that work for the asymmetric conjugate addition of cyclohexanone to nitroolefins are described. The catalysts worked with very low loading (0.5 mol%) in the absence of any additives to provide high diastereo- and enantio-selectivities.

A formal total synthesis of (6S,7S,9R,10R)-6,9-epoxynonadec-18-ene-7,10-diol from D-glucose

An enantiospecific synthesis of (2R,4S,5S)-tetrahydro-4-hydroxy-5-pentyl-2-furfuraldehyde (benzoate) and (benzylate), key intermediates in the synthesis of the title marine natural product from D-glucose is described

Synthesis of O-spiro-C-aryl glycosides using organocatalysis.

An organocatalysis strategy has been developed toward the synthesis of O-spiro-C-aryl glycosides with different configurations in the sugar part. This strategy has been extended to the synthesis of the Papulacandin class of compounds.

Identification of New Molecular Entities (NMEs) as Potential Leads against Tuberculosis from Open Source Compound Repository

The purpose of this study was to provide a number of diverse and promising early-lead compounds that will feed into the drug discovery pipeline for developing new antitubercular agents. The results from the phenotypic screening of the open-source compound library against Mycobacterium smegmatis and Mycobacterium bovis (BCG) with hit validation against M. tuberculosis (H37Rv) have identified novel potent hit compounds. To determine their druglikeness, a systematic analysis of physicochemical properties of the hit compounds has been performed using cheminformatics tools. The hit molecules were analysed by clustering based on their chemical finger prints and structural similarity determining their chemical diversity. The hit compound library is also filtered for druglikeness based on the physicochemical descriptors following Lipinski filters. The robust filtration of hits followed by secondary screening against BCG, H37Rv and cytotoxicity evaluation has identified 12 compounds with potential against H37Rv (MIC range 0.4 to 12.5 μM). Furthermore in cytotoxicity assays, 12 compounds displayed low cytotoxicity against liver and lung cells providing high therapeutic index > 50. To avoid any variations in activity due to the route of chemical synthesis, the hit compounds were re synthesized independently and confirmed for their potential against H37Rv. Taken together, the hits reported here provides copious potential starting points for generation of new leads eventually adds to drug discovery pipeline against tuberculosis.

Total Synthesis of Lamellarin D Trimethyl Ether, Lamellarin D, and Lamellarin H

Total syntheses of three different lamellarins have been accomplished using a Ru(II)-catalyzed (3 + 2) annulation strategy to construct the central pyrrole ring. The striking features of this synthesis are the use of PEG-400 as a green solvent for the (3 + 2) annulation reaction and multiple catalytic reactions with excellent overall yield. The present route also enables the synthesis of various lamellarin analogues devoid of a B ring.

Synthesis and biological evaluation of strained unusual amino acid containing tetrapeptides as potential antidepressant agents.

Strained unusual amino acid derived tetrapeptides were synthesized as mimics of GLYX-13, a clinical candidate for neuroprotective and anti-depressant properties, were studied. The synthesized compounds were screened for neurite growth and anti-depressant properties in vitro and in vivo respectively comparing with the parent GLYX-13 compound. Neurite growth property was assessed by neurite length and anti-depressant property by percentage of immobility in forced swim test, a behavioural assay. Mechanistic insights about protein-ligand interactions were obtained using molecular docking study. Based on the in vitro and in vivo screening data and molecular docking study, a new analogue of GLYX-13, Compound 11a has been found to be as good as the parent compound in all respects.

Synthesis of Terminal Oligosaccharides from Type Specific Lipooligosaccharide of Mycobacterium Tuberculosis

Abstract The coupling reaction between 1,3-di-O-acetyl-4-O-benzyl-2-O-methyl-α-L-rhamnopyranose (9) and methyl 4-O-benzyl-2-O-methyl-α-L-rhamno-pyranoside (4) was carried out in the presence of boron trifluoride-etherate followed by deacetylation to give the disaccharide (11) containing a free 3′ position. The second glycosylation reaction with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide in the presence of mercuric salts followed by removal of benzyl and acetyl groups provided the trisaccharide 2. The boron trifluoride catalysed condensation of 1,3,4-tri-O-acetyl-2-O-methyl-L-fucopyranose (14) and methyl 2,4,6-tri-O-benzyl-α-d-glucopyranoside (15) gave the disaccharide (16) from which the protecting groups were removed to form the disaccharide (3).

HDAC inhibitor misprocesses bantam oncomiRNA, but stimulates hid induced apoptotic pathway

Apoptosis or programmed cell death is critical for embryogenesis and tissue homeostasis. Uncontrolled apoptosis leads to different human disorders including immunodeficiency, autoimmune disorder and cancer. Several small molecules that control apoptosis have been identified. Here, we have shown the functional role of triazole derivative (DCPTN-PT) that acts as a potent HDAC inhibitor and mis-express proto onco microRNA (miRNA) bantam. To further understanding the mechanism of action of the molecule in apoptotic pathway, a series of experiments were also performed in Drosophila, a well known model organism in which the nature of human apoptosis is very analogous. DCPTN-PT mis processes bantam microRNA and alters its down regulatory target hid function and cleavage of Caspase-3 which in turn influence components of the mitochondrial apoptotic pathway in Drosophila. However regulatory microRNAs in other pro-apoptotic genes are not altered. Simultaneously, treatment of same molecule also affects the mitochondrial regulatory pathway in human tumour cell lines suggesting its conservative nature between fly and human. It is reasonable to propose that triazole derivative (DCPTN-PT) controls bantam oncomiRNA and increases hid induced apoptosis and is also able to influence mitochondrial apoptotic pathway.

Expanding the tetrahydroquinoline pharmacophore

Tetrahydroquinoline is a privileged scaffold with a large number of biological applications. The tetrahydroquinoline pharmacophore has been expanded to yield 34 compounds. Biological screening of these compounds led to the identification of tetrahydroquinoline as neurotropic agents not reported earlier.