Current Topics in Medicinal Chemistry - Volume 14, Issue 8, 2014

Phytochemistry accords with phytochemicals which are obtained from a plant source. In recent years, there is a great insistence to phytochemical constituents as they are devoid of adverse reactions. On account of lack of modern scientific evidence for their basis of action on diseases, a crude extract is not well accepted. But due to the adverse side effects & increasing failure of modern drugs to cure the ailments, the attention has been turned back towards ancient systems of medicine, such as, Ayurveda, Unani and Chinese. Consequently, plants have once again attained the centre stage in the efforts aimed at developing effective drugs for diseases incurable by modern medicine system. Hence, the present issue was aimed to point out the in detail study of the phytochemical compounds including but not limited to isolation, structure elucidation, in silico studies(molecular docking, QSAR etc) and assessment of therapeutic potential which would aid in understanding the chemical structures better as therapeutic agent.

Chemical investigation of Crateva adansonii DC has led to the isolation of aurantiamide acetate, a novel ethyl pyropheophorbide A, purpurin-18 ethyl ester and pyropheophorbide A. Their structures were elucidated using extensive spectral data. These metabolites were then evaluated for their in vitro bioactivity against the African trypanosome Trypanosoma brucei brucei (S427) blood stream forms. Anti-trypanosomal activity decreased with aurantiamide acetate (MIC 25μ M), while it increased with the pheopytins (MIC 6.25μM), when compared to the standard drug Suramin. Using the Vlife MDS 4.3 - GRIP docking, these phytoconstituents were then tested to identify the proteins targeted and the mode of activity employed. Their affinity towards the receptor sites of trypanothione reductase, riboflavin kinase, rohedsain, glutathione synthetase & sterol-14α-demethylase (CYP51) of Trypanosoma brucei were evaluated according to the resulting docking energies.

The activation of transcription factors nuclear factor-kappa B (NF-κ B) and cyclooxygenase-2 (COX-2) is critical in cancer; they act synergistically in promoting tumor growth, survival, and resistance to chemotherapy. Thus, combined targeting of NF-κ B and COX-2 present an opportunity for synergistic anticancer efficacy. The ester prodrugs of pentacyclic triterpenoids reduced lantadene A (3), B (4), and its congener 22β-hydroxyoleanonic acid (5) with various non steroidal anti-inflammatory drugs (NSAIDs) present a novel approach. The ester prodrugs of 3 and 4 with diclofenac showed promising dual inhibition of NF-κ B and COX-2. The lead prodrugs 14 and 15 exhibited inhibition of inhibitor of nuclear factor-kappa B kinaseβ (IKKβ ) in the single-digit micromolar range and at the same time, prodrugs 14 and 15 showed marked cytotoxicity against A549 lung cancer cell line with IC50s 0.15 and 0.42 μM, respectively. The prodrugs 14 and 15 exhibited stability in the acidic pH and were hydrolyzed readily in the human blood plasma to release the active parent moieties. Thus, we have synthesized novel hybrid compounds to target both NF-κ B and COX-2 via a prodrug approach, leading to promising anticancer candidates.

As a part of our anticancer drug discovery programme, QSAR models were developed for the prediction of anticancer activities of ursolic acid derivatives against the human hepatocellular carcinoma HepG2, breast carcinoma MDA-MB-231 and the human ductal breast epithelial T47D cancer cell lines followed by wet lab semi-synthesis of virtually active derivatives, their in-vitro biological evaluation and apoptosis. The development of QSAR models was carried out by forward stepwise multiple linear regression method using a leave-one-out approach. Virtually active derivatives were semi synthesized, spectroscopically characterized and then in-vitro tested against human cancer cell lines. Active derivatives were checked via DNA fragmentation assay. The results exhibited regression coefficients (r2) and the cross-validation regression coefficients (rCV2) for the human HepG2, MDA-MB-231 and T47D cancer cell lines as .95 and .90; .92 and .87; .89 and .83 respectively showing the prediction accuracy of the models against biological activities. Computational molecular modeling is a valid modern approach, widely used in the identification of potential drug leads. The most active virtual derivatives of UA were semi- synthesized and their in-vitro and ex-vivo evaluation showed similar results with the predicted one, validating our QSAR models. Out of several active derivatives, the three UA2, UA7 and UA10 were potentially active against the above human cancer cell lines. These findings may be of immense importance in the anticancer drug development of an inexpensive and widely available natural product, ursolic acid.

Chemical investigation of the lichen Cetraria islandica has led to the isolation of four compounds identified as protolichesterinic acid, lichesterinic acid, protocetraric acid and fumarprotocetraric acid. Their structures were characterized using their physical and spectroscopic data. Using an Alamarblue™ 96 well microplate assay, these compounds were tested to evaluate their trypanocidal activity against Trypanosoma brucei brucei. Protolichesterinic acid (MIC = 6.30 μM) and lichesterinic acid (MIC = 12.5 μM) showed very significant activity against the test organism. Docking studies (GRIP technique) of these molecules revealed their strong affinity towards possible targets of Trypanosoma brucei such as riboflavin kinase, sterol-14α-demethylase (CYP51), rohedsain and glutathione synthetase. Hydrophobicity played a significant role in their antitrypanosomal activity.

Chagas disease causes considerable morbimortality in the Americas, with circa 7 to 8 million infected people, causing at least 12,000 annual deaths and 100 million people at risk. Its chemotherapy is poorly selective and effective, associated to severe side effects and unresponsive cases. Thus, R&D on therapeutic alternatives is undoubtedly required. The Brazilian poorly studied biodiversity offers uncountable bioagents, which may be exploited for chemotherapy. The triterpene arjunolic acid (AA), reduced the Trypanosoma cruzi epimastigote in vitro proliferation with an apparent IC50 of 171 μM. Electron microscopy analysis revealed remarkable effects on the parasite surface and architecture. AA-treated parasites displayed minutely corrugated plasma membranes devoid of subpellicular microtubules as well as biogenesis of multiple basal bodies. As the AA effects appeared mainly restricted or originated at the parasite peripheral cytoplasm, including the cytoskeleton membrane linkage, we inferred that the compound targeted primarily the lipid bilayer; therefore, we performed synthetic modification to increase the molecule lipophilicity and thus membrane permeability. The methyl ester (MeAA) and tri-acetylated derivatives (3AcAA) had potentiated trypanocidal activity, producing IC50 values of 21.9 and 15.8 μM, respectively. Both derivatives were able to produce remarkable ultrastructural alterations in the parasites, including inner compartments such as Golgi apparatus and the endocytic/autophagic pathway. Parasites cultured with both derivatives displayed numerous and large autophagic vacuoles, altered flagellar length and cell body connection. These data indicate that synthetically-modified natural products comprise valuable tools in antiparasitic chemotherapy and that electron microscopy may be useful not only in determining the mechanisms of action but also in directing such modifications for rational drug design.

The activity of the enzyme steroid sulfatase (STS) is high in breast tumors and elevated levels of STS mRNA expression have been associated with a poor prognosis. Potent STS irreversible inhibitors have been developed, paving the way to use this new type of therapy for the treatment of breast cancer. Several small molecules belonging to a natural products-inspired library of previously obtained inhibitors of tumor cell growth and new molecules planned to be reversible inhibitors of this enzyme were docked into STS. Some of the synthesized xanthone derivatives, which revealed high scores against STS, namely oxo-9H-xanthene-3,6-diyl bis(3-chlorobenzoate) (5), 9-oxo-9H-xanthene-3,6-diyl bis(4-tertbutylbenzoate) (6) and 9-oxo-9H-xanthene-3,6-diyl bis(4-methoxybenzoate) (7) showed poor water solubility. Therefore, formulations of these derivatives with cyclodextrins were prepared and characterized. The compounds were evaluated regarding their effect on the in vitro growth of various human tumor cell lines, as well as the effect in STS inhibition, for the compounds with the most favorable ΔG values. Additionally, the capacity of these derivatives and of some prenyl and acetoxy-benzophenone and xanthones to inhibit the in vitro growth of MCF-7 ER(+) and/or to inhibit STS in a micromolar range was also assessed. Some compounds developed in the present work were shown to be potential STS inhibitors.

Phyllanthus amarus is a medicinal herb used in traditional Indian medicine for liver disorders. Several researches also show that it acts primarily in the liver, but the molecules were unidentified for liver protective activity. This study was to determine whether the lignans isolated from P. amarus attenuates the D-galactosamine (GalN) / Lipopolysaccharide (LPS)- induced acute hepatitis in mice. Standardize mixture of lignans (slPA) isolated from leaves of P. amarus using automated chromatographic technique was used for experiments. Experimental mice were orally pre-treated with slPA (10, 30 and100mg/kg) for 7 days before intra-peritoneal injection of GalN/LPS. Acute hepatitis in mice was confirmed by significant increase of pro-inflammatory cytokines, and hepatotoxic markers. Pre-treatment of slPA exhibit significant liver protection in dose dependant mannaer. In-silico molecular docking studies also suggests that lignans are preferentially more active due to strong binding affinity against pro-inflammatory cytokines; IL-1β, IL-6, and TNF-α. The electronic parameters of lignans for bioavailability, drug likeness and toxicity were within the acceptable limit. In-vivo and in-silico results suggest that pretreatment of slPA exhibit potent hepatoprotection against GalN/LPS-induced hepatitis in mice and the liver protective effects may be due to the inhibition of inflammatory mediators.

Indole alkaloids and synthetic indole derivatives are well known for their therapeutic importance. In fact, preclinical and clinical studies had already demonstrated several pharmacological activities for these compounds. Here, we overview the multifunctional potential of these molecules for the inhibition of enzymes related to neurodegenerative disease: acetylcholinesterase (AChE), butyrylcholinesterase (BChE), monoamine oxidases A and B (MAO-A and MAO-B). A focus will be given on Psychotria L. genus, considering its reported central effects. Finally, three Psychotria alkaloids, namely desoxycordiofoline (61), bahienoside A (64) and bufotenine (65), along with the synthetic indole derivatives (5S)- 5-(1H-indol-3-ylmethyl)imidazolidine-2,4-dione (66), 5-(1H-indol-3-ylmethyl)-2-thioxoimidazolin-4-one (67), 5-(1Hindol- 3-ylmethyl)-3-methyl-2-thioxoimidazolidin-4-one (68), and methyl 2-(aminoN-(2-(4-methylcyclohex-3-enyl)propan- 2-yl)methanethioamino)-3-(1H-indol-3-yl)propanoate (69), were evaluated in vitro regarding their interactions with AChE, BChE, MAO-A and MAO-B. It was observed that 66 and 68 were able to inhibit MAO-A activity with IC50 value of 8.23 and 0.07 μM. Molecular docking calculations were performed in order to understand the interactions between both ligands (66 and 68) and MAO-A. It was observed that the indole scaffold of both compounds bind into the MAO-A active site in the same orientation, establishing van der Waals contacts with lipophilic amino acids. Additionally, the hydantoin ring of 66 is able to interact by hydrogen bonds with two conserved water molecules in the MAO-A active site, while the methyl-thiohydantoin ring of 68 is within hydrogen bond distance from the hydrogen atom attached to the (N-5) of FAD cofactor. Taking together, our findings demonstrate that the indolyl-hydantoin and indolylmethyl-thiohydantoin rings might consists of good scaffolds for the development of new MAO-A inhibitors possessing neuroprotective properties.

Enyne derivatives isolated from terrestrial plants and fungi have recently attracted attention due to their interesting biological activities. It was found that these derivatives possess in general potent antiinflammatory activity which was attributed to the structural similarity of enynes with the natural antiinflammatory agents secreted in the human body. The biosynthesis of some of the isolated enynes has been proposed based on detailed isotope labeling studies. Computational calculations have been utilized to analyze the conformational preferences and forces affecting interaction of some enynes with the target binding sites. Synthesis of enynes has been achieved using several coupling techniques. In the current review we shed some light on the isolation, biological activity, and biosynthetic routes of enynes. We also recount different synthetic methodologies developed for the synthesis of compounds containing enyne functional group.