Metal- and Phenol-Free Synthesis of Biaryl Ethers: Access to Dibenzobistriazolo-1,4,7-oxadiazonines and Vancomycin-Like Glyco-Macrocycles as Antibacterial Agents.

An efficient synthesis of biaryl ethers, from electron-deficient aryl halides using NaH/DMSO under metal- and phenol-free conditions, has been achieved to access dibenzo-bistriazolo-1,4,7-oxadiazonines and vancomycin-like glyco-macrocycles. A 44-membered glyco-macrocycle showed promising activity against vancomycin-resistant Staphylococcus aureus (VRSA).

Robust turn structures in α3ß cyclic tetrapeptides induced and controlled by carbo-ß3 amino acid.

Designing cyclic tetrapeptides (CTPs), which fold into desired structures, is often a challenging task. While it is difficult to synthesize them, they are also prone to adopt multiple conformations. In this paper we report the synthesis and conformational studies of CTP mimics, having nonconstrained α(3)ß motif, that exhibit stable ß- and γ-turn structures. We also demonstrate the transformation of ß-turn to γ-turn structure in similar CTPs by inverting the chirality of ß(3) carbon in C-linked-carbo-ß(3)-amino acid (Caa) from R to S.

Accessing a small library of pluripotent 1,4,5-trisubstituted 1H-1,2,3-triazoles via diversity-oriented synthesis.

Diversity-oriented synthesis of structurally different, novel and small drug like molecules based on 1,4,5-trisubstituted 1,2,3-triazoles is developed in a streamlined sequence of different sets of reactions. The method involves the use of simple, readily available and highly economical substrates and reagents. The molecules developed herein have potential to be exploited either as chemotherapeutic agents or as scaffolds for other biologically active compounds.

Synthesis of 5-aryl-6-cinnamoyl-7-methyl-flavanones as novel antioxidants and antihyperlipidemics.

An economical and efficient one-pot synthesis of a series of novel 5-aryl-6-cinnamoyl-7-methyl-flavanones has been developed by simple refluxing of cinnamoyl chalcones with NaOAc in aqueous ethanol in quantitative yields. These flavanones were screened for their in vitro antioxidant and in vivo antidyslipidemic activities. Among 24 compounds screened, four compounds 28, 29, 30, and 48 showed significant antidyslipidemic activities. However, out of all the compounds, only compound 28 exhibited significant antioxidant activity and other compounds showed moderate antioxidant activities.

Application of butenonyl-C-glucosides in the synthesis of pyrazolinyl-, aminopyrimidinyl- and biphenyl methyl-ß-D-C-glucopyranosides.

An access to different glycohybrids involving nucleophilic addition of N- and C-nucleophiles to the butenonyl glycosides followed by cyclization and subsequent reactions is reported. In the present communication, three different prototypes, ß-D-glucopyranosylmethyl pyrazolines, ß-D-glucopyranosylmethyl pyrimidines and ß-D-glucopyranosylmethyl biphenyls, were prepared in moderate to good yields.

Synthesis and anti breast cancer activity of biphenyl based chalcones.

A series of (2E,2'E)-1,1'-(3-hydroxy-5-methylbiphenyl-2,6-diyl)-bis(3-pheylprop-2-ene-1-ones (5-33) were prepared by the reaction of 1,3-diacetyl biphenyls (1-4) with different aldehydes in presence of catalytic amount of solid KOH in ethanol in excellent yields. The compounds were evaluated for anticancer activity against human breast cancer MCF-7 (estrogen responsive proliferative breast cancer model) and MDA-MB-231 (estrogen independent aggressive breast cancer model) cell lines, HeLa (cervical cancer) cell line, and human embryonic kidney (HEK-293) cells. Most of the compounds preferentially inhibited the growth of the aggressive human breast cancer cell lines, MDA-MB-231 in the range of 4.4-30 µM. The two compounds 9 and 29 proved to be better anticancer agents than the standard drug tamoxifen against the MDA-MB-231 cell lines. Mode of action of these compounds was established to be apoptosis, cell cycle arrest and loss of mitochondrial membrane potential.

Synthesis and bio-evaluation of alkylaminoaryl phenyl cyclopropyl methanones as antitubercular and antimalarial agents.

A series of 4-alkylaminoaryl phenyl cyclopropyl methanones (6a-6u and 8a-8c) were synthesized from 4-fluorochalcones (3a and 3b) by cyclopropanation of double bond followed by nucleophilic substitution of F with different amines. The compounds were screened for their antitubercular and antimalarial activities against Mycobacterium tuberculosis H37Rv and Plasmodium falciparum 3D7 strains in vitro respectively. Several compounds (6a, 6d-6h, 6p, 6q and 8a-8c) exhibited good in vitro antitubercular activities with MIC values 3.12-12.5µg/mL and preferentially inhibited the growth of P. falciparum in vitro (4a, 4c, 6a-6d, 6f, 6s, 8a and 8c) with IC50 as low as 0.080 and 0.035µg/mL and SI values 4975 and 6948, respectively. Molecular docking studies and in vitro evaluation against FAS-II enzymes using reporter gene assays were carried out to elucidate the mode of action of these molecules. Two compounds 4a and 6g showed significant inhibition at 25µM concentration of the compound.

Glycosylated-imidazole aldoximes as reactivators of pesticides inhibited AChE: Synthesis and in-vitro reactivation study.

The present armamentarium of commercially available antidotes provides limited protection against the neurological effects of organophosphate exposure. Hence, there is an urgent need to design and develop molecules that can protect and reactivate inhibited-AChE in the central nervous system. Some natural compounds like glucose and certain amino acids (glutamate, the anion of glutamic acid) can easily cross the blood brain barrier although they are highly polar. Glucose is mainly transported by systems like glucose transporter protein type 1 (GLUT1). For this reason, a series of non-quaternary and quaternary glycosylated imidazolium oximes with different alkane linkers have been designed and synthesized. These compounds were evaluated for their in-vitro reactivation ability against pesticide (paraoxon-ethyl and paraoxon-methyl) inhibited-AChE and compared with standards antidote AChE reactivators pralidoxime and obidoxime. Several physicochemical properties including acid dissociation constant (pKa), logP, logD, HBD and HBA, have also been assessed for reported compounds. Out of the synthesized compounds, three have exhibited comparable potency with a standard antidote (pralidoxime).

Synthetic studies in butenonyl C-glycosides: Preparation of polyfunctional alkanonyl glycosides and their enzyme inhibitory activity.

A simple synthesis of phenyl butenoyl C-glycosides has been achieved by Aldol condensation of peracetylated glycosyl acetones with aromatic aldehydes followed by deacetylation with methanolic NaOMe. The selected butenoyl C-glycosides on conjugate addition of diethyl malonate resulted in polyfunctional alkanonyl glycosides in good yields. The butenoyl C- and alkanoyl C-glycosides were evaluated for their alpha-glucosidase, glucose-6-phosphatse and glycogen phosphorylase enzyme inhibitory activities in vitro. Three of the synthesized (3, 5 and 9) showed potent enzyme inhibitory activities as compared to standard drugs. Compounds 3, 5 and 9 were evaluated in vivo too displaying significant activity as compared to standard drugs acarbose and metformin.

Solution-phase synthesis of a library of carbapeptide analogues based on glycosylamino acid scaffolds and their in silico screening and antimicrobial evaluation.

A well-organized and efficient approach toward the solution phase synthesis of a library of carbapeptide analogues based on glycosyl amino ester scaffold is described. The reported synthetic route involves a five step preparation of heptofuranuronamides 6a-h and octopyranuronamide 7e from glycosyl amino esters 1 and 7, respectively. Coupling of glycosyl amino esters 1 or 7 with three different N-Fmoc protected amino acids afford the N-Fmoc protected intermediates 2a-c and 7a. Deprotection of Fmoc group in 2a-c and 7a with piperidine gave respective compounds 3a-c and 7b with free amine. Subsequent coupling of 3a-c and 7b with different aromatic acids furnishes respective heptofuranuronates 4a-h and octopyranuronate 7c in good yields. The latter, on ester hydrolysis by LiOH gave the corresponding glycopeptide analogues 5a-h and 7d with terminal carboxyl group. The carboxyl group in these compounds was amidated with oxalyl chloride/ NH(4)OH to afford heptofuranuronamides 6a-h and octopyranuronamides 7e. In vitro screening of all compounds displayed moderate antifungal, antitubercular, and general antibacterial activities. Reverse docking calculations involving over 841 protein drug targets have identified two potential targets for these compounds. These results will form the basis for synthesizing second-generation antimicrobial compounds.

Identification of dual role of piperazine-linked phenyl cyclopropyl methanone as positive allosteric modulator of 5-HT2C and negative allosteric modulator of 5-HT2B receptors.

Allosteric modulators of G-protein-coupled receptors have lately gained significant traction in drug discovery. Recent studies have shown that allosteric modulation of serotonin 2C receptor (5-HT2C) as a viable strategy for the treatment of various central nervous system (CNS) disorders. Considering the critical role of 5-HT2C in the modulation of appetite, a selective positive allosteric modulator (PAM) of 5-HT2C offers a new opportunity for anti-obesity therapeutic development. In this study, phenyl cyclopropyl-linked N-heterocycles were synthesized and evaluated at 5-HT2C for agonist and PAM activity. Our study shows that imidazole linked phenyl cyclopropyl methanones has PAM activity on both 5-HT2C and serotonin 2B receptor (5-HT2B). Interestingly, piperazine linked phenyl cyclopropyl methanones (58) was active as PAM of 5-HT2C (increased the Emax of 5-HT to 139%), and as negative allosteric modulator (NAM) of 5-HT2B (decreases EC50 of 5-HT 10 times without affecting Emax). Similar effect of compound 58 was observed with synthetic orthosteric agonist lorcaserin on 5-HT2B. Molecular docking study revealed that all active compounds were binding to the predicted allosteric site on 5-HT2C and shared a common interacting residues. Finally, compound 58 suppressed food intake in Sprague Dawley (SD) rats similar to lorcaserin after i.c.v. administration. Therefore, these results suggest that piperazine moiety is essential for dual activity (PAM & NAM) of compounds 58, and supports the hypothesis of 5-HT2C PAM for the treatment of obesity similar to the full agonist.

Evaluation of Mycobacterium smegmatis as a possible surrogate screen for selecting molecules active against multi-drug resistant Mycobacterium tuberculosis.

New and better drugs are needed for tuberculosis (TB), particularly for the multi-drug resistant (MDR) disease. However, the highly infectious nature of MDR Mycobacterium tuberculosis restricts its use for large scale screening of probable drug candidates. We have evaluated the potential of a screen based on a 'fast grower' mycobacterium to shortlist compounds which could be active against MDR M. tuberculosis. Sensitivity profiles of M. smegmatis, M. phlei and M. fortuitum as well as MDR clinical isolates of M. tuberculosis were determined against anti-TB drugs isoniazid and rifampicin. Among the three fast growers, M. smegmatis was found to display a profile similar to MDR M. tuberculosis. Subsequently we evaluated the performance of M. smegmatis as a 'surrogate' screen for 120 compounds which were synthesized for anti-TB activity. Fifty of these molecules were active against M. tuberculosis H(37)Rv at a minimum inhibitory concentration (MIC) cutoff of

Asymmetric organocatalysis with glycosyl-beta-amino acids: direct asymmetric aldol reaction of acetone with aldehydes.

Direct asymmetric aldol reaction of acetone with aromatic aldehydes was achieved in good yields and high enantioselectivity using 5-amino-5-deoxy-beta-L-ido-(alpha-D-gluco)-heptofuranuronic acids as a new class of organocatalysts.

DBU assisted expeditious synthesis of glycosyl dienes via glycosylated beta-hydroxy esters.

DBU catalyzed condensation of 3-O-benzyl(methyl)-5,6-dideoxy-1,2-O-isopropylidene-beta-L-threo-hept-4-enofuranuronates with different aldehydes produces the corresponding 3-O-benzyl(methyl)-6-carbethoxy-5,6-dideoxy-1,2-O-isopropylidene-7-phenyl-beta-L-threo-hept-4-enofuranoses. The latter on treatment with methanesulfonyl chloride followed by DBU catalyzed E2 reaction of the methanesulfonyloxy intermediates gave the respective 3-O-benzyl(methyl)-6-carbethoxy-5,6,7-trideoxy-1,2-O-isopropylidene-7-phenyl-beta-L-threo-hept-4,6-dienofuranose in moderate to good yields.

An efficient synthesis of tetramic acid derivatives with extended conjugation from L-ascorbic acid.

BACKGROUND: Tetramic acids with polyenyl substituents are an important class of compounds in medicinal chemistry. Both solid and solution phase syntheses of such molecules have been reported recently. Thiolactomycin, a clinical candidate for treatment of tuberculosis has led to further explorations in this class. We have recently developed an efficient synthesis of tetramic acids derivatives from L-ascorbic acid. In continuation of this work, we have synthesised dienyl tetramic acid derivatives. RESULTS: 5,6-O-isopropylidene-ascorbic acid on reaction with DBU led to the formation of tetronolactonyl allyl alcohol, which on oxidation with pyridinium chlorochromate gave the respective tetranolactonyl allylic aldehydes. Wittig olefination followed by reaction of the resulting tetranolactonyl dienyl esters with different amines resulted in the respective 5-hydroxy lactams. Subsequent dehydration of the hydroxy lactams with p-toluene sulphonic acid afforded the dienyl tetramic acid derivatives. All reactions were performed at ambient temperature and the yields are good. CONCLUSION: An efficient and practical method for the synthesis of dienyl tetramic acid derivatives from inexpensive and easily accessible ascorbic acid has been developed. The compounds bear structural similarities to the tetramic acid based polyenic antibiotics and thus this method offers a new and short route for the synthesis of tetramic acid derivatives of biological significance.

Synthesis and anticancer activity of γ-(triazolyl ethylidene)butenolides and polyfunctional pyrrolinones.

A series of novel γ-(triazolyl ethylidene)butenolides (4-23) were prepared from commercially available l-ascorbic acid in good yields. These butenolides on reaction with ethanolic ammonia/amines led to formation of respective 5-hydroxy pyrrolinones (24-33). The two of these pyrrolinones on dehydration with p-toluenesulfonic acid, were transformed into γ-(triazolyl ethylidene)pyrrolinones (34, 35). Among all the newly synthesized hybrid molecules tested for anticancer activity in vitro, compounds 24, 25, 26, 27, 28, 30 and 32 showed significant activity against MCF-7, MDA-MB-231, PC-3 or U-937 cells. In particular compound 25 (IC50 = 11.3 µM) exhibited most potent activity against breast cancer cells and preliminary studies revealed that potency of this compound is due to ROS generation, subsequent activation of p38, leading to apoptosis and inhibition of cancer cells.

Carbohydrate based potential chemotherapeutic agents: recent developments and their scope in future drug discovery.

In addition to being valuable source of energy, carbohydrates, one of the main dietary components, are integral parts of the cell. As extra- & intracellular molecules they act as cell surface receptor and also as signaling molecules playing predominant role in molecular recognition and many other cellular processes. The clear understanding of their role in the various important biological events has led to the demand for easy access of diverse glycoconjugates for their complete chemical and biological investigations. Several carbohydrate-based molecules both of synthetic and natural origin are known for their wide range of pharmacological activities and even many of them are clinically used to treat different ailments. Due to their structural diversity in terms of functional groups, ring size and linkages they are valuable scaffolds in drug discovery processes. Because of the hydrophilic nature of monosaccharides they offer good water solubility, optimum pharmacokinetics and decreased toxicity. These naturally occurring molecules have therefore been extensively used to access diverse library of compounds with great chemotherapeutic importance. This review highlights an overview of development of carbohydrate-based molecules from others and our lab which have shown promising biological activity against front line diseases.

One pot efficient diversity oriented synthesis of polyfunctional styryl thiazolopyrimidines and their bio-evaluation as antimalarial and anti-HIV agents.

An efficient one pot synthesis of a series of pluripotent (E)-1-(3-methyl-5-aryl-7-styryl-5H-thiazolo[3,2-a]pyrimidin-6-yl)-3-arylprop-2-en-1-ones is reported. It involves reaction of 5-acetyl-6-methyl-4-aryl-dihydropyrimidine-2-thiones, propargyl bromide and aromatic aldehydes in presence of ethanolic KOH. The newly synthesized compounds were evaluated for antimalarial activity against Plasmodium falciparum and as HIV-RT inhibitors. Most of the compound displayed potent antimalarial activity with IC(50)<2 µg/mL. Compounds 6, 11 and 20 showed better activity against P. falciparum K1 strains in comparison to standard drug chloroquine. Compounds 6, 11, and 16 exhibited 73.44, 66.92, and 70.81% HIV-RT inhibition at 100 µg/mL.

Application of click chemistry towards an efficient synthesis of 1,2,3-1H-triazolyl glycohybrids as enzyme inhibitors.

An efficient synthesis of novel 1,2,3-1H-triazolyl glycohybrids with two or more than two sugar units or a chromenone moiety via copper-catalysed azide-alkyne cycloaddition (CuAAC), a 1,3-dipolar cycloaddition of glycosyl azides to 2,3-unsaturated alkynyl glycosides or propargyloxy coumarins is described. The synthesised glycohybrids were screened for their α-glucosidase, glycogen phosphorylase and glucose-6-phosphatase inhibitory activities. A few of the glycohybrids showed promising inhibitory activities against these enzymes.

A convenient synthesis of novel pyranosyl homo-C-nucleosides and their antidiabetic activities.

A series of pyranosyl homo-C-nucleosides have been synthesized by reaction of butenonyl C-glycosides (5a-5j, and 8) and cyanoacetamide in presence of t-BuOK followed by further modifications. The reaction proceeds by Michael addition of cyanoacetamide to the butenonyl C-glycosides and subsequent dehydrative cyclization and oxidative aromatization to give glycosylmethyl pyridones (6a-6j, 7a-7j, 9, and 10). The glycosylmethyl pyridones (6a-6e) on reaction with POCl(3) under reflux gave respective glycosylmethyl pyridines (11a-11e and 12a-12e) in good yields. The synthesized compounds were screened for their in vitro α-glucosidase, glucose-6-phosphatase and glycogen phosphorylase inhibitory activities. One of the pyridylmethyl homo-C-nucleoside, compound 11d, displayed 52% inhibition of glucose-6-phosphatase as compared to the standard drug sodium orthovanadate while compound 12a showed a significant antihyperglycemic effect of 17.1% in the diabetic rats as compared to the standard drug metformin.