Comparison of extraction efficiency and selectivity between low-temperature pressurized microwave-assisted extraction and prolonged maceration.

Extraction is a key step in studying compounds from plants and other natural sources. The common use of high temperatures in pressurized microwave-assisted extraction (PMAE) makes it unsuitable for the extraction of compounds with low or unknown thermal stability. This study aimed at determining the suitability of low-temperature, short-time PMAE in attaining yields comparable to those of prolonged maceration at room temperature. Additionally, we explored the phytochemical differences of the extracts from both techniques. Maceration at room temperature for 24 hr and PMAE at 40-45°C and 10 bar for 30 min were carried out on 18 samples from 14 plant species at a solvent-to-feeds ratio of 10. The PMAE yields of 16 out of 18 samples were within the proportions of 91-139.2% as compared with the respective extracts from maceration. Varying numbers of nonmatching peaks were noted in MS chromatograms of five extract pairs, indicating selective extraction of some compounds. Low-temperature PMAE can attain reasonable extraction efficiency with the added value of sparing compounds of low thermal stability. The method can also enable the recovery of compounds distinct from those obtained by maceration.

Matrix-assisted laser desorption/ionization tandem mass spectrometry of N-glycans derivatized with isonicotinic hydrazide and its biotinylated form.

RATIONALE: Successful structural characterization of glycans often requires derivatization prior to mass spectrometric analysis. Here we report on a new derivatization reagent for glycans, biotinylated isonicotinic hydrazide, allowing glycan analysis by both mass spectrometry (MS) and biochemically. Fragmentation behavior in MS and its use in structural elucidation were investigated and compared with other labels. METHODS: Glycans, released from ribonuclease B and ovalbumin, were derivatized with hydrazine labels (isoniazid (INH), biotinylated isonicotinic hydrazide (BINH) and biotinamidocaproylhydrazide (BACH)). In addition, native counterparts and 2-aminobenzamide (2-AB) derivatives were prepared. Comparative matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI TOF/TOF) experiments were carried out to investigate the fragmentation pattern of the derivatives. Finally, the capability of BINH derivatives to bind lectins was explored. RESULTS: Generally, derivatization provided beneficial enhancement in the mass spectrometric signal intensity as compared to native counterparts. The mass spectrometric fragmentation varied with the kind of label used. The most significant structure-revealing ions (cross-ring cleavages) were observed in the spectra of BINH derivatives, whereas mainly glycosidic cleavages were found with native form of glycans and 2-AB derivatives. CONCLUSIONS: Hydrazine derivatization provided the means to obtain structurally informative fragment ions. Due to BINH derivatization, specific fragments of the isomers allowed the identification of diverse glycans. The derivatization reaction can be carried out without the need for purification. The biotin residue of BINH enabled for biochemical studies, i.e. protein-glycan interactions.

Structure-activity relationships of strychnine analogs at glycine receptors.

Nine strychnine derivatives including neostrychnine, strychnidine, isostrychnine, 21,22-dihydro-21-hydroxy-22-oxo-strychnine, and several hydrogenated analogs were synthesized, and their antagonistic activities at human α1 and α1ß glycine receptors were evaluated. Isostrychnine has shown the best pharmacological profile exhibiting an IC50 value of 1.6 µM at α1 glycine receptors and 3.7-fold preference towards the α1 subtype. SAR Analysis indicates that the lactam moiety and the C(21) = C(22) bond in strychnine are essential structural features for its high antagonistic potency at glycine receptors.

Dualsteric GPCR targeting: a novel route to binding and signaling pathway selectivity.

Selective modulation of cell function by G protein-coupled receptor (GPCR) activation is highly desirable for basic research and therapy but difficult to achieve. We present a novel strategy toward this goal using muscarinic acetylcholine receptors as a model. The five subtypes bind their physiological transmitter in the highly conserved orthosteric site within the transmembrane domains of the receptors. Orthosteric muscarinic activators have no binding selectivity and poor signaling specificity. There is a less well conserved allosteric site at the extracellular entrance of the binding pocket. To gain subtype-selective receptor activation, we synthesized two hybrids fusing a highly potent oxotremorine-like orthosteric activator with M(2)-selective bis(ammonio)alkane-type allosteric fragments. Radioligand binding in wild-type and mutant receptors supplemented by receptor docking simulations proved M(2) selective and true allosteric/orthosteric binding. G protein activation measurements using orthosteric and allosteric blockers identified the orthosteric part of the hybrid to engender receptor activation. Hybrid-induced dynamic mass redistribution in CHO-hM(2) cells disclosed pathway-specific signaling. Selective receptor activation (M(2)>M(1)>M(3)) was verified in living tissue preparations. As allosteric sites are increasingly recognized on GPCRs, the dualsteric concept of GPCR targeting represents a new avenue toward potent agonists for selective receptor and signaling pathway activation.

In search of novel agents for therapy of tropical diseases and human immunodeficiency virus.

Malaria, sleeping sickness, Chagas' disease, Aleppo boil, and AIDS are among the tropical diseases causing millions of infections and cases of deaths per year because only inefficient chemotherapy is available. Since the targeting of the enzymes of the polyamine pathway may provide novel therapy options, we aimed to inhibit the deoxyhypusine hydroxylase, which is an important step in the biosynthesis of the eukaryotic initiation factor 5A. In order to identify new lead compounds, piperidines were produced and biologically evaluated. The 3,5-diethyl piperidone-3,5-dicarboxylates 11 and 13 substituted with 4-nitrophenyl rings in the 2 and 6 positions were found to be active against Trypanosoma brucei brucei and Plasmodium falciparum combined with low cytotoxicity against macrophages. The corresponding monocarboxylates are only highly active against the T. brucei brucei. The piperidine oximether 53 demonstrated the highest plasmodicidal activity. Moreover, compounds 11 and 53 were also able to inhibit replication of HIV-1.

Random chemistry as a new tool for the generation of small compound libraries: development of a new acetylcholinesterase inhibitor.

Random chemistry, the serendipitous generation of small compound libraries by gamma-irradiation of source compounds, presents a methodology providing reassembled and rearranged structures. The gamma-irradiation was applied to generate new acetylcholinesterase (AChE) inhibitors. The bioassay-guided fractionation as a deconvolution strategy was employed to analyze gained product mixture. The structure of the new highly potent AChE inhibitor, 9-amino-5,6,7,8-tetrahydroacridin-4yl)methanol (1), was elucidated by NMR spectroscopy and ESI (tandem) mass spectrometry.

Development of a new type of allosteric modulator of muscarinic receptors: hybrids of the antagonist AF-DX 384 and the hexamethonio derivative W84.

Various fragments of the hexamethonio-type allosteric agent W84 were linked to the secondary amino group of the muscarinic M(2) acetylcholine receptor-preferring antagonist AF-DX 384 to increase the area of attachment with the allosteric site. Addition of only the phthalimido moiety of W84 gave an allosteric enhancer of NMS binding. Thus, a new lead structure for the development of allosteric enhancers of NMS binding has been discovered.

Allosteric small molecules unveil a role of an extracellular E2/transmembrane helix 7 junction for G protein-coupled receptor activation.

G protein-coupled receptors represent the largest superfamily of cell membrane-spanning receptors. We used allosteric small molecules as a novel approach to better understand conformational changes underlying the inactive-to-active switch in native receptors. Allosteric molecules bind outside the orthosteric area for the endogenous receptor activator. The human muscarinic M(2) acetylcholine receptor is prototypal for the study of allosteric interactions. We measured receptor-mediated G protein activation, applied a series of structurally diverse muscarinic allosteric agents, and analyzed their cooperative effects with orthosteric receptor agonists. A strong negative cooperativity of receptor binding was observed with acetylcholine and other full agonists, whereas a pronounced negative cooperativity of receptor activation was observed with the partial agonist pilocarpine. Applying a newly synthesized allosteric tool, point mutated receptors, radioligand binding, and a three-dimensional receptor model, we found that the deviating allosteric/orthosteric interactions are mediated through the core region of the allosteric site. A key epitope is M(2)Trp(422) in position 7.35 that is located at the extracellular top of transmembrane helix 7 and that contacts, in the inactive receptor, the extracellular loop E2. Trp 7.35 is critically involved in the divergent allosteric/orthosteric cooperativities with acetylcholine and pilocarpine, respectively. In the absence of allosteric agents, Trp 7.35 is essential for receptor binding of the full agonist and for receptor activation by the partial agonist. This study provides first evidence for a role of an allosteric E2/transmembrane helix 7 contact region for muscarinic receptor activation by orthosteric agonists.

Random chemistry as a new tool for the generation of small-compound libraries.

Advances in modern medicinal chemistry have enabled scientists to engineer new pathways aiming at the generation of novel chemical entities. Random chemistry, the serendipitous synthesis of small-compound libraries by gamma-irradiation of a highly active lead compound or pharmacophoric fragments of active compounds, represents a complementary methodology, which provides both, compounds with resembling molecular structure and rearranged structures not previously known. Since the libraries are likely to be derived from radical chemistry, Fenton's reagent was applied to a methanol/water solution of tacrine to mimic the irradiation. Indeed, the experiment resulted in a similar product spectrum as found for tacrine in water and methanol solutions after (60)Co irradiation. However, the application of Fenton's reagent is limited due to its poor solubility in organic solvents. Since the drugs we are aiming for should exhibit high water solubility, this limitation can be regarded as an advantage at the same time. Further extension of the random chemistry approach led to the successful irradiation of non-active but drugable single fragments and combinations of fragments, i.e. the irradiation of tetrahydroisoquinoline and benzylamine, both being fragments of naphthylisoquinolines with antiplasmodial activity. The obtained isoquinoline derivatives were found to exhibit anti-infective activities and thus are promising new lead structures.

Atypical muscarinic allosteric modulation: cooperativity between modulators and their atypical binding topology in muscarinic M2 and M2/M5 chimeric receptors.

The binding and function of muscarinic acetylcholine receptors can be modulated allosterically. Some allosteric muscarinic ligands are "atypical", having steep concentration-effect curves and not interacting competitively with "typical" allosteric modulators. For atypical agents, a second allosteric site has been proposed. Different approaches have been used to gain further insight into the interaction with M2 receptors of two atypical agents, tacrine and the bispyridinium compound 4,4'-bis-[(2,6-dichloro-benzyloxy-imino)-methyl]-1,1'-propane-1,3-diyl-bispyridinium dibromide (Duo3). Interaction studies, using radioligand binding assays and the allosteric ligands obidoxime, Mg2+, and the new tool hexamethonium to antagonize the allosteric actions of the atypical ligands, showed different modes of interaction for tacrine and Duo3 at M2 receptors. A negatively cooperative interaction was observed between hexamethonium and tacrine (but not Duo3). A tacrine dimer that exhibited increased allosteric potency relative to tacrine but behaved like a typical allosteric modulator was competitively inhibited by hexamethonium. M2/M5-receptor mutants revealed a dependence of tacrine and Duo3 affinity on different receptor epitopes. This was confirmed by docking simulations using a three-dimensional model of the M2 receptor. These showed that the allosteric site could accommodate two molecules of tacrine simultaneously but only one molecule of Duo3, which binds in different mode from typical allosteric agents. Therefore, the atypical actions of tacrine and Duo3 involve different modes of receptor interaction, but their sites of attachment seem to be the "common" allosteric binding domain at the entrance to the orthosteric ligand binding pocket of the M2-receptor. Additional complex behavior may be rationalized by allosteric interactions transmitted within a receptor dimer.

Photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with acetylene: an effective method for the synthesis of 2-pyridines under mild conditions.

The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines.