Peter Imming

Syntheses and evaluation of halogenated cytisine derivatives and of bioisosteric thiocytisine as potent and selective nAChR ligands.

We have developed one-step syntheses of halogenated derivatives of (-)-cytisine featuring a halogen substituent at positions 3, 5 or 3 and 5 of the 2-pyridone fragment, and prepared the novel bioisosteric thiocytisine by oxygen-sulphur exchange. The affinities of these pyridone-modified analogs of (-)-cytisine for (alpha 4)(2)(beta 2)(3) and alpha 7* nAChRs in rat forebrain membranes were determined by competition with (+/-)-[(3)H]epibatidine and [(3)H]MLA, respectively. The 3-halocytisines 7 possess subnanomolar affinities for (alpha 4)(2)(beta 2)(3) nAChRs, higher than those found for (-)-cytisine as well as for the 5-halocytisines 8 and 3,5-dihalocytisines 6. In contrast to the parent alkaloid the 3-halogenated species display much a higher affinity for the alpha 7* nAChR subtype. The most potent molecule was 3-bromocytisine (7b) with preferential selectivity (200-fold) for the (alpha 4)(2)(beta 2)(3) subtype [K(i)=10 pM (alpha 4 beta 2) and 2.0 nM (alpha 7*)]. Replacement of the lactam with a thiolactam pharmacophore to thiocytisine (12) resulted in a subnanomolar affinity for the (alpha 4)(2)(beta 2)(3) nAChR subtype (K(i)=0.832 nM), but in a drastic decrease of affinity for the alpha 7* subtype; thiocytisine (12) has a K(i) value of 4000 nM (alpha 7*), giving a selectivity of 4800-fold for the neuronal (alpha 4)(2)(beta 2)(3)-nAChR and thus displaying the best affinity-selectivity profile in the series under consideration.

AN IMPROVED SYNTHETIC PROCEDURE FOR 6,6′-DIBROMOINDIGO (TYRIAN PURPLE)

Tyrian purple was the most precious dye of antiquity. We describe a simple synthetic procedure that yields the actual dye, 6,6′-dibromoindigo 1, in considerably improved overall yield and of analytical purity, also being amenable to scale-up.

New Analgesics Synthetically Derived from the Paracetamol Metabolite N-(4-Hydroxyphenyl)-(5Z,8Z,11Z,14Z)-icosatetra-5,8,11,14-enamide

N-(4-hydroxyphenyl)-(5Z,8Z,11Z,14Z)-icosatetra-5,8,11,14-enamide (AM404) is a metabolite of the well-known analgesic paracetamol. AM404 inhibits endocannabinoid cellular uptake, binds weakly to CB1 and CB2 cannabinoid receptors, and is formed by fatty acid amide hydrolase (FAAH) in vivo. We prepared three derivatives of this new (endo)cannabinoid using bioisosteric replacement (1), homology (2), and derivatization (3) of the 4-aminophenol moiety in AM404 and tested them against CB1, CB2, and FAAH. We found affinities toward both cannabinoid receptors equal to or greater than that of AM404. Shortening the acyl chain from C20 to C2 led to three new paracetamol analogues: N-(1H-indazol-5-yl)acetamide (5), N-(4-hydroxybenzyl)acetamide (6), and N-(4-hydroxy-3-methoxyphenyl)acetamide (7). Again, 5, 6, and 7 were tested against CB1, CB2, and FAAH without significant activity. However, 5 and 7 behaved like inhibitors of cyclooxygenases in whole blood assays. Finally, 5 (50 mg/kg) and 6 (275 mg/kg) displayed analgesic activities comparable to paracetamol (200 mg/kg) in the mouse formalin test.

Evaluation of the endogenous cannabinoid system in mediating the behavioral effects of dipyrone (metamizol) in mice

Dipyrone is a common nonopioid analgesic and antipyretic, which, in many countries, is available over the counter and is more widely used than paracetamol or aspirin. However, the exact mechanisms by which dipyrone acts remain inconclusive. Two novel arachidonoyl-conjugated metabolites are formed in mice following the administration of dipyrone that are dependent on the activity of fatty acid amide hydrolase (FAAH), which also represents the major catabolic enzyme of the endogenous cannabinoid ligand anandamide. These arachidonoyl metabolites not only inhibit cyclooxygenase (COX-1/COX-2) but also bind to cannabinoid receptors at low micromolar concentrations. The relative contributions of cannabinoid receptors and FAAH in the overall behavioral response to dipyrone remain untested. Accordingly, the two primary objectives of the present study were to determine whether the behavioral effects of dipyrone would (a) be blocked by cannabinoid receptor antagonists and (b) occur in FAAH−/− mice. Here, we report that thermal antinociceptive, hypothermic, and locomotor suppressive actions of dipyrone are mediated by a noncannabinoid receptor mechanism of action and occurred after acute or repeated administration irrespective of FAAH. These findings indicate that FAAH-dependent arachidonoyl metabolites and cannabinoid receptors are not requisites by which dipyrone exerts these pharmacological effects under noninflammatory conditions.

CYP2C19 progress curve analysis and mechanism-based inactivation by three methylenedioxyphenyl compounds.

Several in vitro criteria were used to assess whether three methylenedioxyphenyl (MDP) compounds, the isoquinoline alkaloids bulbocapnine, canadine, and protopine, are mechanism-based inactivators of CYP2C19. The recently reported fluorometric CYP2C19 progress curve analysis approach was applied first to determine whether these alkaloids demonstrate time-dependent inhibition. In this experiment, bulbocapnine, canadine, and protopine displayed time dependence and saturation in their inactivation kinetics with KI and kinact values of 72.4 ± 14.7 μM and 0.38 ± 0.036 min−1, 2.1 ± 0.63 μM and 0.18 ± 0.015 min−1, and 7.1 ± 2.3 μM and 0.24 ± 0.021 min−1, respectively. Additional studies were performed to determine whether other specific criteria for mechanism-based inactivation were fulfilled: NADPH dependence, irreversibility, and involvement of a catalytic step in the enzyme inactivation. CYP2C19 activity was not significantly restored by dialysis when it had been inactivated by the alkaloids in the presence of a NADPH-regenerating system, and a metabolic-intermediate complex-associated increase in absorbance at approximately 455 nm was observed. In conclusion, the CYP2C19 progress curve analysis method revealed time-dependent inhibition by these alkaloids, and additional experiments confirmed its quasi-irreversible nature. This study revealed that the CYP2C19 progress curve analysis method is useful for identifying novel mechanism-based inactivators and yields a wealth of information in one run. The alkaloids bulbocapnine, canadine, and protopine, present in herbal medicines, are new mechanism-based inactivators and the first MDP compounds exhibiting quasi-irreversible inactivation of CYP2C19.

Effects of metabolites of the analgesic agent dipyrone (metamizol) on rostral ventromedial medulla cell activity in mice

The molecular mechanism of action of dipyrone, a widely used antipyretic and non-opioid analgesic drug, is still not fully understood. Actions upon peripheral inflamed tissues as well as the central nervous system, especially upon the PAG-RVM axis, have been suggested. Dipyrone is a prodrug and its activity is due to its immediate conversion to its active metabolites. We tested the effect of two recently discovered metabolites of dipyrone, the arachidonoyl amides of 4-methylaminoantipyrine and 4-aminoantipyrine, on the neurons of the rostral ventromedial medulla (RVM), which are part of the descending pathway of antinociception. These compounds reduced the activity of ON-cells and increased the activity of OFF-cells. Both CB1 and TRPV1 blockade reversed these effects, suggesting that the endocannabinoid/endovanilloid system takes part in the analgesic effects of dipyrone.

Inverse [4+1] Cycloadditions of 3-Methyl-2,3-dihydro-1,3-benzothiazole-2-ylidene with 1,2,4,5-Tetrazines

[4 + 1] Cycloadditions of the nucleophilic singlet carbene 3-methyl-2,3-dihydro-1,3-benzothiazole-2-ylidene (2) with the electron-deficient s-cis-fixed diazadiene systems of a series of substituted 1,2,4,5-tetrazines (4a-c), with CF 3 , SCH 3 and C 6 H 5 -groups are described together with some unexpected follow-up reactions

Molecular Targets of Natural Drug Substances: Idiosyncrasies and Preferences

All creatures - bacteria, plants, animals, humans - have many building blocks in common, down to biochemical structures and information processing languages. That is why natural substances seem to be better able to bind, and bind specifically, to drug targets in man, and to interact specifically with human biochemical networks. Property analyses of a large number of combinatorial and natural products and drugs have revealed the greater chemical similarity of the latter two. How about target preferences of natural products in comparison to synthetic drugs? On the basis of a comprehensive compilation and analysis of molecular targets of drug substances irrespective of their origin, the review categorises targets chemically and analyses the nature of drug targets. The dynamics of drug action are highlighted because an effective drug target comprises a biochemical system rather than a single molecule. The review is restricted to targets of natural compounds that are in use as therapeutic agents, comparing them with targets of marketed drugs in general. Differences are traced to historical, chemical, pharmacological, and social reasons. To give an example, the prevalence of natural products among antibacterial agents seems to be derived from, first, the necessity to have several hydrophilic binding sites for strong and lasting attachment to vital targets of bacteria, and synthetic drug candidates tend to be more hydrophobic than natural compounds. Second, other microorganisms are well equipped with - natural, of course - compounds with defensive or symbiotic functions that interfere with bacterial metabolism.

Products of the Determination of the Iodine Value with Iodine Monobromide

The iodine value (iodine number) is an important analytical characteristic of fats and oils. Leading pharmacopeias determine it using iodine monobromide (Hanuš method). We used methyl oleate as a simple analog of unsaturated triacylglycerols to identify the products. After performing the reaction in deuterated solvents under pharmacopeial conditions, NMR spectroscopy revealed the presence of the 9, 10‐diiodo, 9, 10‐dibromo, and 9, 10‐bromoiodo adducts, leaving no educt olefin. The prescribed subsequent addition of potassium iodide led to the formation of methyl 9, 10‐diiodo and bromoiodo stearate in equal amounts.