Fluorinated phenylcyclopropylamines. Part 5: Effects of electron-withdrawing or -donating aryl substituents on the inhibition of monoamine oxidases A and B by 2-aryl-2-fluoro-cyclopropylamines.

A series of racemic, diastereoisomeric aryl cyclopropylamines substituted with fluorine in the 2-position and electron-donating and electron-withdrawing groups on the aromatic ring have been prepared. These represent analogues of the classic MAO inhibitor tranylcypromine (trans-2-phenylcyclopropylamine, 1). Their activities as inhibitors of recombinant human liver monoamine oxidases A (MAO A) and B (MAO B) were determined. The trans-compounds were low micromolar inhibitors of both MAO A and MAO B with moderate MAO A selectivity while the less active cis-analogues were MAO B selective. In the trans-series, electron-withdrawing para-substituents increased the potency of MAO A inhibition while electron-donating groups such as methyl or methoxy had no influence on this activity. In contrast, aromatic ring substitution in the trans-series had essentially no effect on the inhibition of MAO B. The corresponding cis-compounds were shown to be 10-100 times less active against MAO A, while trans- and cis-compounds were quite similar in terms of inhibition of MAO B. The best MAO A/MAO B selectivity (7:1) in the trans-series was found for trans-2-fluoro-2-(para-trifluoromethylphenyl)cyclopropylamine (7d), while a 1:27 selectivity was found for cis-2-fluoro-2-(para-fluorophenyl)cyclopropylamine (10c). These results are discussed in connection with the pK(a) and logD values, the mechanism of action of tranylcypromines, and the geometry of the active site of the enzymes.

Fluorinated phenylcyclopropylamines. 2. Effects of aromatic ring substitution and of absolute configuration on inhibition of microbial tyramine oxidase.

A series of para-substituted diastereopure cis- and trans-2-fluoro-2-arylcyclopropylamines were synthesized and these were investigated as inhibitors of microbial tyramine oxidase from Arthrobacter sp. All compounds were shown to be competitive inhibitors of this enzyme. The nature of the para-substituents in the more potent trans-isomer (cis-relationship between fluorine and the amino group) of 2-fluoro-2-arylcyclopropylamine influenced the inhibitory potency in a consistent fashion. Thus, electron-withdrawing groups (F, Cl) slightly decreased the activity, while the methyl group (+ I substituent) increased the activity by a factor of ca. 7 compared to trans-2-fluoro-2-phenylcyclopropylamine and by a factor of 90 compared to tranylcypromine. Activity also was strongly dependent on the absolute configuration. The (1S,2S)-enantiomer of 2-fluoro-2-phenylcyclopropylamine was an excellent inhibitor of tyramine oxidase whereas the (1R,2R)-enantiomer was essentially devoid of activity.

Fluorinated phenylcyclopropylamines. Part 3: Inhibition of monoamine oxidase A and B.

Fluorinated phenylcyclopropylamines and alkylamines were examined as inhibitors of recombinant human liver monoamine oxidase A (MAO A) and B (MAO B). For a series of trans- and cis-2-fluoro-2-phenylcyclopropylamine analogues, the presence of fluorine attached to a cyclopropane ring was found to result in an increase in inhibitory activity towards both MAO A and B. In addition, p-substitution of electron-withdrawing groups such as Cl and F in the aromatic ring of the trans-isomers increased the inhibition of both enzymes. (1S,2S)-2-Fluoro-2-phenylcyclopropylamine was a more potent inhibitor of both MAO A and B than was the (1R,2R)-enantiomer, indicating that the presence of fluorine has no influence on the enantioselectivity of MAO inhibition, since a similar effect of stereochemistry has been reported for tranylcypromine. Interestingly, fluorination at the 2-position of 1-phenycyclopropylamine, which is known as a selective inhibitor of MAO B relative to MAO A, reversed the selectivity and resulted in a potent inhibitor selective for MAO A. All inhibitors showed time- and concentration-dependent inhibition for both enzymes, with the exception of trans-2-fluoro-2-phenylcyclopropyl ethylamine, which acts as a competitive and reversible MAO A selective inhibitor.

Fluorinated phenylcyclopropylamines. 1. Synthesis and effect of fluorine substitution at the cyclopropane ring on inhibition of microbial tyramine oxidase.

Two series of diastereopure phenylcyclopropylamine analogues, 2-fluoro-2-phenylcyclopropylamines and 2-fluoro-2-phenylcyclopropylalkylamines, as well as 2-fluoro-1-phenylcyclopropylamines and 2-fluoro-1-phenylcyclopropylmethylamines, were synthesized in order to study the effects of fluorine substitution on monoamine oxidase inhibition. Inhibitory activity was assayed using commercially available microbial tyramine oxidase. Characterization of tyramine oxidase, carried out prior to the inhibition experiments, confirmed earlier suggestions that this enzyme is a semicarbazide-sensitive copper-containing monoamine oxidase. The most potent competitive inhibitor was trans-2-fluoro-2-phenylcyclopropylamine, which had an IC(50) value 10 times lower than that of the nonfluorinated compound, tranylcypromine. 2-Fluoro-1-phenylcyclopropylmethylamine was found to be a weak noncompetitive inhibitor of tyramine oxidase. The presence of a free amino group, directly bonded to the cyclopropane ring, and a fluorine atom in a relationship cis to the amino group were structural features that increased tyramine oxidase inhibition.

Synthesis and antiviral activity of monofluorinated cyclopropanoid nucleosides.

Diastereopure monofluorinated cyclopropanoid nucleosides were synthesized for biological studies. As key intermediates cis- and trans-(+/-)-[1-fluoro-2-(acetoxymethyl)cyclopropyl]methanol were prepared starting from diastereopure fluorinated cyclopropanecarboxylates. The latter were synthesized by copper(i)-catalyzed cyclopropanation of [small alpha]-fluorostyrene with ethyl diazoacetate. After reduction and O-acetylation the diastereomeric (2-fluoro-2-phenylcyclopropyl)methyl acetates were obtained. Oxidative degradation using RuO(4) and reduction of the formed carboxyl group with borane gave the fluorinated alcohols, which were coupled with different nucleobases. After deprotection, the corresponding cyclopropanoid nucleosides of adenine, cytosine, guanine, thymine and uracil were obtained. Antiviral tests revealed for the cis-configured guanosine a low, but specific activity against HSV-1 and HSV-2. In addition low affinities of the adenine derivatives to adenosine receptors were detected.