Novel spiroanellated 1,2,4-trioxanes with high in vitro antimalarial activities

A remarkable increase in antimalarial in vitro activity was achieved by integration of spiroadamantane motifs in 6-alkylidene 1,2,4-trioxanes 3a-h via diastereoselective photooxygenation of allylic alcohols and subsequent BF(3)-catalyzed peroxyacetalization with adamantanone to give the active compounds 3e-h.     

Stereoselective synthesis of desloratadine derivatives as antagonist of histamine

A series of desloratadine derivatives were stereoselectively synthesized and evaluated for H₁ antihistamine activity. For the evaluation of H₁ antihistamine activity, the in vitro histamine-induced contraction of the guinea-pig ileum assay (HC) was used. The synthesized desloratadine derivatives 7, 8 and 9 are structurally related to rupatadine and were generated by replacement of the 5-methyl-3-pyridine group of rupatadine with γ-alkylidene butenolide. Their H₁ antihistamine activities have shown a high dependence on the exact nature of the substituent in the lactone ring. Optimum structures 7, 8a and 8g display potent activity inhibiting histamine-induced effects.     

4-Alkylidenyl glutamic acids, potent and selective GluR5 agonists

Twenty-four 4-alkylidene glutamic acids were synthesised and tested as potential subtype selective GluR5 and 6 ligands. It was found that a critical size of alkylidene group gave potent and selective GluR5 receptor agonists. LY339624 had Kis of 0.0326 and >100 microM on GluR5 and 6 receptors, respectively.     

Synthesis of antitumor 6-alkylidenepenicillanate sulfones and related 3-alkylidene-2-azetidinones

6-alkylidenepenicillanate sulfoxides and sulfones were synthesized on the base of 6-oxopenicillanate esters. The targeted splitting of their thiazolidine ring led to the formation of 3-alkylidene substituted 4-heteryldithio and 4-methylsulfonyl azetidin-2-ones. Some of mono and bicyclic beta-lactams revealed potent cytotoxic properties towards monolayer tumor cells in <10-microM concentrations.     

Polar 3-alkylidene-5-pivaloyloxymethyl-5′-hydroxymethyl-γ-lactones as protein kinase C ligands and antitumor agents

A series of DAG-lactones with polar 3-alkylidene substituents have been investigated as PKC-α ligands and antitumor agents. Extensive analysis of structure–activity relationships for the 3-alkylidene chain revealed that polar groups such as ether, hydroxyl, aldehyde, ester, acyloxy, and amido were tolerated with similar binding affinities and reduced lipophilicities compared to the corresponding unsubstituted alkylidene chain. Among the derivatives, compounds 5, 6 and 8 with an ether type of side chain showed high binding affinities in range of K_i = 3–5 nM and excellent antitumor profiles, particularly against the colo205 colon cancer and the K562 leukemia cell lines.     

Synthesis and biological activities of novel 4"-alkylidene avermectin derivatives

Horner-Emmons reaction of 4"-dehydro-5-O-TBDMS-avermectin B(1a) with a variety of phosphorus ylides using LHMDS gave novel 4"-alkylidene avermectin derivatives in high yields. Further modifications led to derivatives bearing diverse functional groups. The new avermectin derivatives showed potent growth inhibitory activity against Artemia salina and Caenorhabditis elegans.     

Synthesis of andrographolide derivatives: a new family of alpha-glucosidase inhibitors

Andrographolide (1), the cytotoxic agent of the plant Andrographis paniculata, was subjected to semi-synthetic studies leading to a series of new derivatives, a novel family of glucosidase inhibitors. Nicotination of 3,19-hydroxyls in 15-alkylidene andrographolide derivatives (9) was favorable to alpha-glucosidase inhibition activity. Among them, 15-p-chlorobenzylidene-14-deoxy-11,12-didehydro-3,19-dinicotinateandrographolide (11c) was a very potent inhibitor against alpha-glucosidase with an IC50 value of 6 microM. However, all compounds concerned for beta-glucosidase showed no inhibition. All compounds synthesized were characterized by the analysis of NMR, IR, HRMS spectra and the stereochemistry of 2 was confirmed by X-ray analysis.     

R- and S-alkylidene acetals of adenosine: Stereochemical probes for the active site of adenosine deaminase

Condensation of adenosine with unsymmetrical ketones leads to 2′,3′-O-alkylidene acetals with a new chiral center. The diastereoisomers were separated chromatographically, and the ratio of products was found to be 3:1. The configuration of the new chiral centers was determined by nmr spectrosopy. The diastereoisomers were used as stereochemical probes for the active site of adenosine deaminase. By determination of the K_m values it was shown that the binding of the S-diastereoisomers is strongly decreased in comparison with the R-compounds. The data imply a close proximity of the 2′,3′-site of the ribose moiety to the active site of adenosine deaminase.     

Stable spiro-endoperoxides by sunlight-mediated photooxygenation of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-alpha-D-xylo-oct-1,4-furano-7-uloses

Sunlight-mediated photooxygenation of 3-O-acetyl and 3-O-methyl derivatives of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-α-d-xylo-oct-1,4-furano-7-uloses (1a-e) in carbon tetrachloride solution gave stable 4,7-epidioxy derivatives in 4R (2a-e) and 4S (3a-e) configurations. The presence of an endo alkyl, on the 1,2-O-alkylidene group and its size, resulted in an increase of the yield of the 4S isomers. 3-O-Acetyl derivatives yielded products as a mixture of C-7 anomers, whereas 3-O-methyl derivatives gave pure single stereoisomers.     

Digoxin derivatives substituted by alkylidene at the butenolide part

A series of digoxin derivatives containing the γ-alkylidene butenolide moiety were synthesised by way of stereoselective vinylogous aldol reaction of the unactivated butenolide in simple conditions. The structures of compounds synthesised were characterised by infrared (IR), nuclear magnetic resonance (NMR) and HR-MS. Preliminary bioassay shows that some of them have cardiac functions, especially compound 2g that induced a marked increase in myocardial contractility at 10 ng ml⁻¹ and 20 ng ml⁻¹ concentrations without digitalis toxicity.     

4-alkylidene oxazolones as substrates and inhibitors for sensitive assays of the normality of active sites and the catalytic properties of hydrolases

The suitability of eleven 4-alkylidene oxazolones for the determination of four hydrolases, alpha-chymotrypsin, trypsin, carboxylesterase and leucine aminopeptidase, was tested. The specific activities were in general low compared with those obtained with the classical substrates but the Kmapp values were also small. Hence, the kcat/Kmapp ratios of the oxazolones, the optimal indicator of activity, remained in the usual range. The high differential absorption coefficients of the oxazolones in the UV range render these substrates very suitable for the determination of active site normalities if the solubilities of the acyl enzymes and the magnitudes of the rapid bursts are sufficient. Since some of the oxazolones fluoresce, the sensitivity of the method may be increased up to 1000 x by fluorescence detection. The titrations may be carried out in organic solvents, e.g. dimethyl sulphoxide, which greatly stabilize the hydrolases. The high specificity of the oxazolones permits active site titrations in the presence of other hydrolases.     

Antifungal 3,5-disubstituted furanones: From 5-acyloxymethyl to 5-alkylidene derivatives

5-Acetoxymethyl-3-(4-bromophenyl)-2,5-dihydrofuran-2-one previously described as highly antifungally active was found to provide the corresponding 5-methylene derivative via an unusual DMSO-promoted elimination of the ester group at C5 under antifungal assay conditions. Since the latter possessed nearly the same antifungal effect as that originally reported for the former, the 5-acetoxymethyl furanone just served as a precursor of the actual antifungally active species. A few series of compounds with alkyloxy, aryloxy and alkylidene substituents at C5 of the parent furanone structure were therefore prepared and evaluated. In line with the ease of elimination of the substituent from C5, low activities of the 5-alkoxy compounds were observed. On the other hand, their 5-aryloxymethyl congeners were found to be capable of liberating the antifungally active 5-methylene furanone into the testing medium. The antifungal effect of the 5-alkylidene derivatives was highly sensitive to substitution of the alkylidene moiety; a substituent in the allylic position was necessary for a compound to retain high activity. Parallel evaluation of cytostatic activity showed moderate activities of the antifungally active derivatives against HeLa S3 and CCRF-CEM lines. Cell cycle analysis of CCRF-CEM cells following the treatment with 5-methylene-3-(4-bromophenyl)-2,5-dihydrofuran-2-one revealed that this compound is a necrotic agent.     

Assignment of configuration at quaternary centres in pairs of 3-C Hydroxymethyl and 3-C methyl branched chain 1,2:4,6-diacetalated aldohexopyranose derivatives using 13C-N.M.R. spectoscopy

The configuration at the C-3 quaternary carbon atoms in two pairs (1 and 2, 3 and 4) of 3-C-hydroxymethyl, branched-chain, 1,2:4,6-diacetalated aldohexo-pyranoses have been determined from their ¹³ C-n.m.r. spectra. The stereochemical assignments were achieved by comparison of the spectra with those of the Z (13) and E isomers (14) of 4-tert-butyl-l-hydroxymethylcyclohexanol and with those of the corresponding diacetalated gluco- and allo-pyranoses (5, 6, 9, and 10). The spectra of 13 and 14 showed that an axial hydroxyl group shielded the α, β, and μ ring carbon atoms more than an axial hydroxymethyl group and that the carbon atom in the latter group was shielded relative to that in an equatorial hydroxymethyl group The spectra of 5, 6, 9, and 10 indicated the effect of an axial HO-3 on the shifts of the carbon atoms in the 1,2-O-alkylidene groups. The stereochemistry of an isomeric pair of 1,2:4,6-di-O-alkylidene-3-C-methyl-aldohexopyranoses (11 and 12) has also been determined.     

Anticancer potential of labdane diterpenoid lactone “andrographolide” and its derivatives: a semi-synthetic approach

Natural products have been a great source of pharmaceuticals since ages. Vast screening of natural products from different sources has led to the discovery of plethora of chemotherapeutic drugs and other compounds for the betterment of human life. Several bioactive entities have been generated by the structural modifications of the natural products or by using the natives as key models in synthetic chemistry. Nonetheless, a number of natural compounds with potential bioactivities remain unexploited in the medicinal field due to their stringent chemical properties. Andrographis paniculata Nees., a traditional medicinal herb from family Acanthaceae is known for its multiple pharmacological activities. It’s major bioactive constituent “andrographolide”, possesses promising anticancer potential and is one such unexploited treasure. The architecture of the molecule consists of an α-alkylidene γ-butyrolactone moiety, two olefin bond [Δ⁸⁽¹⁷⁾ and Δ¹²⁽¹³⁾], three hydroxyls at C-3, C-19, and C-14 and highly substituted trans decalin. Of the three hydroxyl groups, one is allylic at C-14, and the others are secondary and primary at C-3 and C-19, respectively. By modification of the above structural features a number of andrographolide derivatives have been synthesized. The intricacy of the molecule has always been a constraint in developing a commercialized drug, nevertheless the efforts in this direction via synthetic chemistry are still continuous and prominent. The present review highlights the chemistry and anticancer activity of andrographolide. It discusses the limitations of the molecule as a pharmacological agent. Modifications in the key molecule along different moieties has been discussed which might lead to desirable bioactive molecules. The compiled information will be helpful in further developing specific modifications in andrographolide moiety which will have significant contribution in semi synthesis of anti-cancer agents.     

A comparative study of the conversion of 7-hydroxycholesterol in rabbit,guinea pig,rat, hamster,and chicken

The metabolism of epimeric 7-hydroxycholesterol was studied in vitro. 7Alpha-hydroxycholesterol or 7beta-hydroxycholesterol were incubated with rabbit, guinea pig, rat, hamster, and chicken microsomal suspensions and then extracted and analyzed using high-performance liquid chromatography (HPLC). 7Alpha-hydroxy-4-cholesten-3-one was the main product from 7alpha-hydroxycholesterol in the rabbit, guinea pig, and rat. A considerable amount of 7-ketocholesterol was also produced in the hamster and chicken. In all vertebrates, 7beta-hydroxycholesterol was converted only to 7-ketocholesterol in all vertebrates. 7Beta-hydroxy-4-cholesten-3-one was not detected. Reduction of 7-ketocholesterol was also studied in the rat and hamster. Whereas 7-ketocholesterol was converted to 7beta-hydroxycholesterol in the rat, it was converted to both 7alpha- and 7beta-hydroxycholesterol in the hamster. These results suggest that 7alpha-hydroxycholesterol is converted not only to 7alpha-hydroxy-4-cholesten-3-one but also to 7-ketocholesterol in the hamster and chicken. 7Beta-hydroxycholesterol was converted to 7-ketocholesterol in all vertebrates tested. The interconversion between 7alpha- and 7beta-hydroxycholesterol via 7-ketocholesterol was observed in the hamster in this in vitro study.     

Metabolism of two hydroxy-7-oxocholanic acids in isolated perfused rat liver

The metabolism of 7-oxolithocholic acid and 7-oxodeoxycholic acid in isolated perfused rat livers was compared. The metabolites extracted from the bile of perfused livers were analysed by gas chromatography. The amount of bile acids excreted in bile was greater after infusion with 7-oxolithocholic acid than with 7-oxodeoxycholic acid. When 7-oxolithocholic acid was infused almost all of the bile acids excreted in bile were taurine conjugates; with 7-oxodeoxycholic acid about 10 percent remained unconjugated. 7-Oxolithocholic acid was more susceptible to reduction than 7-oxodeoxycholic acid. 7-Oxolithocholic acid was preferably reduced to 7 beta-hydroxy rather than to 7 alpha-hydroxy metabolites. In contrast, 7-oxodeoxycholic acid was reduced predominantly to the 7 alpha-hydroxy rather than to the 7 beta-hydroxy metabolite.     

The cytosolic domain of protein-tyrosine kinase 7 (PTK7), generated from sequential cleavage by a disintegrin and metalloprotease 17 (ADAM17) and γ-secretase, enhances cell proliferation and migration in colon cancer cells

Protein-tyrosine kinase 7 (PTK7) is a member of the defective receptor protein-tyrosine kinases and is known to function as a regulator of planar cell polarity during development. Its expression is up-regulated in some cancers including colon carcinomas. A 100-kDa fragment of PTK7 was detected in the culture media from colon cancer cells and HEK293 cells. The shed fragment was named sPTK7-Ig1-7 because its molecular mass was very similar to that of the entire extracellular domain of PTK7 that contains immunoglobulin-like loops 1 to 7 (Ig1-7). The shedding of sPTK7-Ig1-7 was enhanced by treatment with phorbol 12-myristate 13-acetate. In addition to the sPTK7-Ig1-7 found in the culture medium, two C-terminal fragments of PTK7 were detected in the cell lysates: PTK7-CTF1, which includes a transmembrane segment and a cytoplasmic domain, and PTK7-CTF2, which lacks most of the transmembrane segment from PTK7-CTF1. Analysis of PTK7 processing in the presence of various protease inhibitors or after knockdown of potential proteases suggests that shedding of PTK7 into sPTK7-Ig1-7 and PTK7-CTF1 is catalyzed by ADAM17, and further cleavage of PTK7-CTF1 into PTK7-CTF2 is mediated by the γ-secretase complex. PTK7-CTF2 localizes to the nucleus and enhances proliferation, migration, and anchorage-independent colony formation. Our findings demonstrate a novel role for PTK7 in the tumorigenesis via generation of PTK7-CTF2 by sequential cleavage of ADAM17 and γ-secretase.     

Two novel proteins, MRL7 and its paralog MRL7-L, have essential but functionally distinct roles in chloroplast development and are involved in plastid gene expression regulation in Arabidopsis

Chloroplast development requires the coordinated action of various proteins, many of which remain to be identified. Here, we report two novel genes, Mesophyll-cell RNAi Library line 7 (MRL7) and MRL7-Like (MRL7-L), that are involved in this process. An Arabidopsis knock-down transgenic plant (MRL7-RNAi) with delayed-greening phenotype was isolated from an RNA interference (RNAi) transformant library. Cotyledons and young leaves of MRL7-RNAi were pale in seedlings and gradually greened as the plant matured, while a knock-out in the MRL7 gene was seedling lethal. The MRL7 protein was shown to co-localize with a marker protein for nucleoids in chloroplasts, indicative of a role for the protein in chloroplast nucleic acid metabolism. Accordingly, chloroplast development was arrested upon loss of MRL7 function and the expression of plastid-encoded genes transcribed by plastid-encoded RNA polymerase (PEP) was significantly reduced in MRL7 knock-down and knock-out plants. A paralog of MRL7 (MRL7-L) was identified in the Arabidopsis genome. Both MRL7 and MRL7-L are only found in land plants and encode previously uncharacterized proteins without any known conserved domain. Like MRL7, knock-down of MRL7-L also resulted in a virescent phenotype, and a similar effect on plastid gene expression. However, the MRL7-L protein was localized to the chloroplast stroma. Taken together, our data indicate that the two paralogous proteins MRL7 and MRL7-L have essential but distinct roles during early chloroplast development and are involved in regulation of plastid gene expression.     

The proteasome alpha-subunit XAPC7 interacts specifically with Rab7 and late endosomes

Rab7 is a key regulatory protein governing early to late endocytic membrane transport. In this study the proteasome alpha-subunit XAPC7 (also known as PSMA7, RC6-1, and HSPC in mammals) was identified to interact specifically with Rab7 and was recruited to multivesicular late endosomes through this interaction. The protein interaction domains were localized to the C terminus of XAPC7 and the N terminus of Rab7. XAPC7 was not found on early or recycling endosomes, but could be recruited to recycling endosomes by expression of a Rab7-(1-174)Rab11-(160-202) chimera, establishing a central role for Rab7 in the membrane recruitment of XAPC7. Although XAPC7 could be shown to associate with membranes bearing ubiquitinated cargo, overexpression had no impact on steady-state ubiquitinated protein levels. Most notably, overexpression of XAPC7 was found to impair late endocytic transport of two different membrane proteins, including EGFR known to be highly dependent on ubiquitination and proteasome activity for proper endocytic sorting and lysosomal transport. Decreased late endocytic transport caused by XAPC7 overexpression was partially rescued by coexpression of wild-type Rab7, suggesting a negative regulatory role for XAPC7. Nevertheless, Rab7 itself was not subject to XAPC7-dependent proteasomal degradation. Together the data establish the first direct molecular link between the endocytic trafficking and cytosolic degradative machineries.