Glycyrrhetinic acid: a promising scaffold for the discovery of anticancer agents.

INTRODUCTION: Oleanane-type pentacyclic triterpenes named glycyrrhetinic acids (GAs) featuring a C-30 carboxylic acid group, are extracted from the licorice (Glycyrrhiza uralensis). Numerous biological properties of GA have been reported and have attracted researchers from all over the world in recent years due to the peculiar GA scaffold-based semisynthetic cytotoxic effects. AREAS COVERED: This review represents the applications of semisynthetic derivatives of GA for the development of future cancer treatments. Included in the review are important structural features of the semisynthetic GAs crucial for cytotoxic effects. EXPERT OPINION: Numerous semisynthetic GA derivatives illustrated excellent cytotoxic effects toward various cancer cells. Notably the C-3(OH) at ring A along with C30-CO2H at ring E as vital structural features, make GA very appealing as a lead scaffold for medicinal chemistry, since these two groups permit the creation of further chemical diversity geared toward improved cytotoxic effects. Furthermore, numerous GA derivatives have been synthesized and indicate that compounds featuring cyanoenone moieties in ring A, or compounds having the amino group or nitrogen comprising heterocycles and hybrids thereof, illustrate more potent cytotoxicity. Furthermore, GA has a great capability to be conjugated with other anticancer molecules to synergistically enhance their combined cytotoxicity.

Cell-free expression and in meso crystallisation of an integral membrane kinase for structure determination.

Membrane proteins are key elements in cell physiology and drug targeting, but getting a high-resolution structure by crystallographic means is still enormously challenging. Novel strategies are in big demand to facilitate the structure determination process that will ultimately hasten the day when sequence information alone can provide a three-dimensional model. Cell-free or in vitro expression enables rapid access to large quantities of high-quality membrane proteins suitable for an array of applications. Despite its impressive efficiency, to date only two membrane proteins produced by the in vitro approach have yielded crystal structures. Here, we have analysed synergies of cell-free expression and crystallisation in lipid mesophases for generating an X-ray structure of the integral membrane enzyme diacylglycerol kinase to 2.28-Å resolution. The quality of cellular and cell-free-expressed kinase samples has been evaluated systematically by comparing (1) spectroscopic properties, (2) purity and oligomer formation, (3) lipid content and (4) functionality. DgkA is the first membrane enzyme crystallised based on cell-free expression. The study provides a basic standard for the crystallisation of cell-free-expressed membrane proteins and the methods detailed here should prove generally useful and contribute to accelerating the pace at which membrane protein structures are solved.

Aromatic lipoxin A4 and lipoxin B4 analogues display potent biological activities.

Lipoxins are a group of biologically active eicosanoids typically formed by transcellular lipoxygenase activity. Lipoxin A4 (LXA4) and Lipoxin B4 (LXB4) biosynthesis has been detected in a variety of inflammatory conditions. The native lipoxins LXA4 and LXB4 demonstrate potent antiinflammatory and proresolution bioactions. However, their therapeutic potential is compromised by rapid metabolic inactivation by PG dehydrogenase-mediated oxidation and reduction. Here we report on the stereoselective synthesis of aromatic LXA4 and LXB4 analogues by employing Sharpless epoxidation, Pd-mediated Heck coupling, and diastereoselective reduction as the key transformations. Subsequent biological testing has shown that these analogues display potent biological activities. Phagocytic clearance of apoptotic leukocytes plays a critical role in the resolution of inflammation. Both LXA4 analogues (1R)-3a and (1S)-3a were found to stimulate a significant increase in phagocytosis of apoptotic polymorphonuclear leukocytes (PMN) by macrophages, with comparable efficacy to the effect of native LXA4, albeit greater potency, while the LXB4 analogue also stimulated phagocytosis with a maximum effect observed at 10-11 M. LX-stimulated phagocytosis was associated with rearrangement of the actin cytoskeleton consistent with that reported for native lipoxins. Using zymosan-induced peritonitis as a murine model of acute inflammation (1R)-3a significantly reduced PMN accumulation.

Synthesis and biological evaluation of isomeric derivatives of naturally occurring spatozoate.

An isomer of the natural phthalate ester spatozoate (1), n-butyl 2-benzoyloxymethylbenzoate (2a) and a series of its new derivatives 2b-2s were synthesized and exposed to selected biological screening, as phthalates were reported to possess different biological activities. Compound 2g was found to be the most potent cytotoxic agent with a LD50 = 8.98 microg/ml. In a bactericidal assay the compounds showed a broad spectrum of activities. Compound 2a has a very promising fungicidal activity against Microsporum canis.

Efficient synthesis of isobenzofuran-1(3H)-ones (phthalides) and selected biological evaluations.

The studies presented here deal with the convenient and efficient one-step conversion of o-alkylbenzoic acids into their corresponding isobenzofuran-1 (3H)-ones (phthalides) using NaBrO3/NaHSO3 in a two-phase system. A range of o-alkylbenzoic acids was used with the object of getting a variety of phthalide derivatives as multipurpose biologically active compounds. Seventeen phthalides have been synthesized and tested for cytotoxicity, antibacterial and antifungal activities. Some of these compounds showed promising cytotoxic effects against Artemia salina. Compounds 4j-4p were highly active against Gram-negative and Gram-positive bacteria among all tested compounds. In the fungicidal assay, the compounds showed a broad spectrum of activity against six fungi. All compounds were characterized via elemental analysis, UV, IR, mass and-NMR spectroscopy.

Synthesis and pharmacological activity of 4-(4'-(chlorophenyl)-4-hydroxypiperidine) derivatives.

A new series of 4-(4'-chlorophenyl)-4-hydroxypiperidine derivatives (2-5), substituted at nitrogen, were synthesized and tested as potential analgesic compounds as well as evaluated for their effect on hypotensive activity. Results showed that all the derivatives exhibit significant analgesic activity in male Wistar rats at a dose of 50 mg/kg of body weight after intramuscular injection, when tested by thermal stimuli (tail flick test). Pethidine was used as reference drug. Compounds 2, 3 and 5 produced reduction in blood pressure in normotensive rat.

Synthesis of methyl ether analogues of sildenafil (Viagra) possessing tyrosinase inhibitory potential.

The microwave-assisted synthesis and characterization of the ten new sildenafil (Viagra; 1) analogues 6-15 are described. A detailed structure-activity-relationship (SAR) study revealed that compounds 10 (= 4-ethoxy-N-hydroxy-3-(7-methoxy-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)benzenesulfonamide) and 12 (= S-(2-hydroxyethyl) 4-ethoxy-3-(7-methoxy-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)benzenesulfonothioate) are extremely potent mushroom tyrosinase inhibitors, with IC50 values (3.59 and 2.15 microM, resp.) below those of the standard inhibitors L-mimosine and kojic acid (IC50 = 3.68 and 16.67 microM, resp.). Compounds 10 and 12 are, thus, the currently most-effective inhibitors of tyrosinase, and bear great potential to be used for the treatment of various skin disorders such as hyperpigmentation, which is associated with high production of melanocytes.

Syntheses, antibacterial, cytotoxic and antifungal effects of new 3-carboxy-l-phenacylpyridinium salts.

Thirteen pyridine-3-carboxylic acid salt derivatives with various substituted phenacyl residues were prepared and their cytotoxicity, antibacterial and antifungal activities tested. Compounds 5 and 11 proved to be active in the brine shrimp bioassay, compounds 7, 9-12 and 14 showed promising antibacterial activities, whereas none of the compounds tested against 15 fungal cultures proved to be active. Extensive spectroscopic techniques were employed to confirm the structure of the synthetic products.