Rashmi Gaur

In vivo anti-diabetic activity of derivatives of isoliquiritigenin and liquiritigenin

Isoliquiritigenin (ISL), a chalcone and liquiritigenin (LTG), a flavonoid found in licorice roots and several other plants. ISL displays antioxidant, anti-inflammatory, antitumor and hepatoprotective activities whereas LTG is an estrogenic compound, acts as an agonist selective for the β-subtype of the oestrogen receptor. Both the phenolics were isolated from the rhizomes of Glycyrrhiza glabra. Five derivatives from ISL and four derivatives from LTG were synthesized. All the compounds were established by extensive spectroscopic analyses and screened through oral glucose tolerance test to gain preliminary information regarding the antihyperglycemic effect in normal Swiss albino male mice. ISL (1), ISL derivatives 3, 4, 5, 7 and LTG derivatives 9 and 10 showed significant blood glucose lowering effect. The structure-activity relationship indicated that the presence of ether and ester groups in ISL and LTG analogues are important for exhibiting the activity. Compounds 1, 4 and 10 were selected for in vivo antidiabetic activity and found to be potential candidates for treatment of diabetes. It is the first report on antidiabetic activity of ISL derivative 4 and LTG derivative 10.

Insect feeding deterrent and growth inhibitory activities of scopoletin isolated from Artemisia annua against Spilarctia obliqua (Lepidoptera: Noctuidae)

Abstract  Artemisia annua (Asteraceae) is well known for its antimalarial activities due to presence of the compound artemisinin. We isolated a methoxy coumarin from the stem part of A. annua and confirmed its identity as scopoletin through mass spectral data. The structure was established from 1H‐nuclear magnetic resonance (NMR), 13C‐NMR. The compound scopoletin was evaluated for its feeding deterrence and growth inhibitory potential against a noxious lepidopteran insect, Spilartctia obliqua Walker. Scopoletin gave FD50 (feeding deterrence of 50%) value of 96.7 μg/g diet when mixed into artificial diet. S. obliqua larvae (12‐day‐old) exposed to the highest concentration (250 μg/g diet) of scopoletin showed 77.1% feeding‐deterrence. In a growth inhibitory assay, scopoletin provided 116.9% growth inhibition at the highest dose of 250 μg/g diet with a GI50 (growth inhibition of 50%) value of 20.9 μg/g diet. Statistical analysis showed a concentration‐dependent dose response relationship toward both feeding deterrent and growth inhibitory activities. Artemisinin is found mainly in the leaves of A. annua and not in the stems, which are typically discarded as waste. Therefore identification of scopoletin in stems of A. annua may be important as a source of this material for pest control.

In vitro and in vivo synergistic interaction of substituted chalcone derivatives with norfloxacin against methicillin resistant Staphylococcus aureus

Thirty chalcone derivatives were synthesized via a base catalyzed Claisen Schmidt condensation and evaluated for their anti-methicillin-resistant Staphylococcus aureus (MRSA) activity alone and in combination with norfloxacin. Among these, 5 derivatives namely trans-3-(1H-indol-3-yl)-1-(4′-benzyloxyphenyl)-2-propen-1-one (2), 1-(4″-biphenyl)-3-(3′4′-dihydroxyphenyl)-2-propen-1-one (11), 1-(4″-hydroxy-3″-methylphenyl)3-(4′-hydroxyphenyl)-2-propen-1-one (14), 3-(4′-chlorophenyl)-1-(4″-hydroxyphenyl)2-propen-1-one (17), and LTG-oxime (27) showed significant antibacterial activity with MIC 12.5–50 µg mL−1 respectively. In combination studies, derivatives 2 and 14 significantly reduced the MIC of norfloxacin by up to 16 fold (FICI < 0.5), while derivatives 11, 17 and 27 reduced it by up to eight fold (FICI ≤ 0.5). Flow cytometry analysis results clearly indicated that derivatives 2 and 14 significantly promote the accumulation and inhibition of the Et-Br efflux, which was further validated through spectrofluorimeter using clinical isolate MRSA-ST2071. In systemically infected Swiss albino mice model, both the compounds significantly (P < 0.001, P < 0.01) lowered the systemic bacterial load in blood, liver, kidney, lung and spleen tissues. This study supports the promising use of chalcones in the development of economical antibacterial combinations.

Molecular Modeling Based Synthesis and Evaluation of In vitro Anticancer Activity of Indolyl Chalcones

A series of twenty one chalcone derivatives having indole moiety were synthesized and were evaluated against four human cancer cell lines. Indolyl chalcones 1a, 1b, 1d, 1f-1j, 2c, 2e, 2i showed good anticancer activity. Chalcones 1b and 1d were the most active and selective anticancer agents with IC50 values <1μg/ml and 1.51μg/ml, against WRL-68 cell line, respectively. Molecular mechanism was explored through in silico docking & ADMET studies.

In vitro antimalarial studies of novel artemisinin biotransformed products and its derivatives

Biotransformation of antimalarial drug artemisinin by fungi Rhizopus stolonifer afforded three sesquiterpenoid derivatives. The transformed products were 1α-hydroxyartemisinin (3), 3.0%, a new compound, 10β-hydroxyartemisinin, 54.5% (4) and deoxyartemisinin (2) in 9% yield. The fungus expressed high-metabolism activity (66.5%). The chemical structures of the compounds were elucidated by 1D, 2D NMR spectrometry and mass spectral data. The major compound 10β-hydroxyartemisinin (4) was chemically converted to five new derivatives 5-9. All the compounds 3-9 were subjected for in vitro anti-malarial activity. 10β-Hydroxy-12β-arteether (8), IC50 at 18.29nM was found to be 10 times better active than its precursor 4 (184.56nM) and equipotent antimalarial with natural drug artemisinin whereas the α-derivative 9 is 3 times better than 4 under in vitro conditions. Therefore, the major biotransformation product 4 can be exploited for further modification into new clinically potent molecules. The results show the versatility of microbial-catalyzed biotransformations leading to the introduction of a hydroxyl group at tertiary position in artemisinin in derivative (3).

Biotransformation of artemisinin derivatives by Glycyrrhiza glabra , Lavandula officinalis , and Panax quinquefolium

Biotransformation of α-artemether and dihydroartemisinin (DHA) by Glycyrrhiza glabra (Linn.), Lavandula officinalis (L.), and Panax quinquefolium was investigated. Two metabolites: tetrahydrofuran derivative (3) and a 13-carbon ring-rearranged product (4) were produced from α-artemether (1). DHA (2) provided metabolite 4. The structure of the metabolites were characterized by proton (1H) and carbon (13C) nuclear magnetic resonance (NMR) imaging, fourier transform infrared spectroscopy, and mass spectroscopy. This is the first report that G. glabra and L. officinalis have the capability to biotransform α-artemether, and P. quinquefolium to biotransform DHA. Metabolite 3 is a new compound and metabolite 4 is reported here for the first time from artemisinin derivatives 1 and 2. The presence of acetate function in the derivative 3 and hydroxyl and C-12 deoxo groups in 4 obtained in our study make them interesting synthones for further modification into new clinically potent molecules.

Isomeric Flavonoids of Artemisia annua (Asterales: Asteraceae) as Insect Growth Inhibitors Against Helicoverpa armigera (Lepidoptera: Noctuidae)

ABSTRACT Artemisia annua (Asterales: Asteraceae) is one of the important natural sources of antimalarial compounds i.e., artemisinin and artemisinic acid. Also this plant is cultivated on a large area in India under industry-farmer partnerships. With a view to enhance the added value of the raw material of A. annua and its chemical constituents, we evaluated methanolic extract of powdered A. annua leaves and different compounds isolated from the extract for toxicity and inhibition and disruption of growth and development of the African pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Methanol extract of A. annua and eight known constituent compounds [artemisinic acid, artemisinin, scopoletin, arteannuin-B, deoxy-artemisinin, artemetin and isomeric flavonoids (casticin and chrysosplenetin)] were bio-assayed for larval mortality, abnormal development, and growth inhibition. The methanol extract severely affected 100% of the larva treated, i.e., larvae gained very little weight, some larvae died, some formed larval-pupal intermediates, some pupae died and a few abnormal adults (adultoids) emerged. The mean weight of treated larvae reached only 0.026 g compared to the 0.270 g in the control and at par with larvae treated with 2% neem seed kernel extract (0.035 g) and 0.02% w/w azadirachtin (0.059 g).Among A. annua constituent compounds, the isomeric flavonoids exhibited a strong reduction in mean larval weight (58.5%), and growth inhibition (50.0%) as compared to the control. Extracts of A. annua and its isomeric flavonoids appear to have potential for developing novel biopesticides.

Drug Resistance Reversal Potential of Isoliquiritigenin and Liquiritigenin Isolated from Glycyrrhiza glabra Against Methicillin‐Resistant Staphylococcus aureus (MRSA)

Isoliquiritigenin (ISL) and liquiritigenin (LTG) are structurally related flavonoids found in a variety of plants. Discovery of novel antimicrobial combinations for combating methicillin‐resistant Staphylococcus aureus (MRSA) infections is of vital importance in the post‐antibiotic era. The present study was taken to explore the in vitro and in vivo combination effect of LTG and ISL with β‐lactam antibiotics (penicillin, ampicillin and oxacillin) against mec A‐containing strains of MRSA. Minimum inhibitory concentration (MIC) of both LTG and ISL exhibited significant anti‐MRSA activity (50–100 µg/mL) against clinical isolates of MRSA. The result of in vitro combination study showed that ISL significantly reduced MIC of β‐lactam antibiotics up to 16‐folds [∑ fractional inhibitory concentration (FIC) 0.312–0.5], while LTG reduced up to 8‐folds (∑FIC 0.372–0.5). Time kill kinetics at graded MIC combinations (ISL/LTG + β‐lactam) indicated 3.27–9.79‐fold and 2.59–3.48‐fold reduction in the growth of clinical isolates of S. aureus respectively. In S. aureus‐infected Swiss albino mice model, combination of ISL with oxacillin significantly (p < 0.05, p < 0.01, p < 0.001) lowered the systemic microbial burden in blood, liver, kidney, lung and spleen tissues in comparison with ISL, oxacillin alone as well as untreated control. Considering its synergistic antibacterial effect, we suggest both ISL and LTG as promising compounds for the development of novel antistaphylococcal combinations. Copyright

In vitro antimalarial activity and molecular modeling studies of novel artemisinin derivatives

Cerebral malaria is a serious and sometimes fatal disease caused by a Plasmodium falciparum parasite that infects a female anopheles mosquito which feeds on humans. The parasites responsible for mosquito-borne infectious diseases are increasingly resistant to current drug approaches, and almost half of the world is at risk of contracting an illness. A series of twenty five new ether and ester derivatives of dihydroartemisinin (DHA) have been prepared based on in silico studies and in vitro antimalarial activity and later assessed against the chloroquine sensitive NF-54 strain of Plasmodium falciparum. In general the incorporation of nitro functionality in ester derivatives enhances the activity relative to artemisinin. Most of the ether derivatives were found to be as active as DHA, while 11-OH ether derivatives were not as active as DHA. The most potent analogue in the series was compound 21 which was several fold more active than artemisinin against P. falciparum used in the study. Molecular docking and ADMET studies were performed to explore the possible mode of interaction of active compounds in to the binding site pocket of malaria parasite target enzyme plasmepsin-II and evaluated compliance with oral bioavailability and pharmacokinetics parameters. The ester derivatives 19 and 20 were found to be twice active than DHA, having nitro functionality showing IC50 10.58 nM and 8.54 nM respectively.

A novel bi-functional chalcone inhibits multi-drug resistant Staphylococcus aureus and potentiates the activity of fluoroquinolones

Staphylococcus aureus is the leading cause of bacteraemia and the dwindling supply of effective antibacterials has exacerbated the problem of managing infections caused by this bacterium. Isoliquiritigenin (ISL) is a plant flavonoid that displays therapeutic potential against S. aureus. The present study identified a novel mannich base derivatives of ISL, IMRG4, active against Vancomycin intermediate S. aureus (VISA). IMRG4 damages the bacterial membranes causing membrane depolarization and permeabilization, as determined by loss of salt tolerance, flow cytometric analysis, propidium idodie and fluorescent microscopy. It reduces the intracellular invasion of HEK-293 cells by S. aureus and decreases the staphylococcal load in different organs of infected mice models. In addition to anti-staphylococcal activity, IMRG4 inhibits the multidrug efflux pump, NorA, which was determined by molecular docking and EtBr efflux assays. In combination, IMRG4 significantly reduces the MIC of norfloxacin for clinical strains of S. aureus including VISA. Development of resistance against IMRG4 alone and in combination with norfloxacin was low and IMRG4 prolongs the post-antibiotic effect of norfloxacin. These virtues combined with the low toxicity of IMRG4, assessed by MTT assay and haemolysis, makes it an ideal candidate to enter drug development pipeline against S. aureus.