Synthesis and structure-activity relationships for new 6-fluoroquinoline derivatives with antiplasmodial activity.

The substitution of 6-fluoroquinolines was modified in ring positions 2 and 4. The new compounds were tested in vitro for their activities against a sensitive and a multidrug resistant strain of Plasmodium falciparum. Some physicochemical parametres were calculated (log P, log D, ligand efficiency) or determined experimentally (permeability). The most promising compounds were tested for their in vivo activity against Plasmodium berghei in a mouse model. The 6-fluoro-2-{4-[(4-methylpiperazin-1-yl)methyl]phenyl}-N-[2-(pyrrolidin-1-yl)ethyl]quinoline-4-carboxamide possessed proper physicochemical properties and showed high antiplasmodial activity in vitro (IC50 ≤ 0.0029 µM) and in vivo (99.6% activity).

Antiprotozoal Activities of Tetrazole-quinolines with Aminopiperidine Linker.

BACKGROUND: Human African Trypanosomiasis (HAT, sleeping sickness) and Malaria both are insect vectored tropical diseases. Only a couple of drugs is able to cure HAT, but all of them are toxic, prone to resistance and require parenteral administration. Malaria is responsible for high morbidity and mortality in humans. It is one of the global killers of children. Wide-spread drug resistance against traditional therapeutics which were once highly effective makes them almost useless. Therefore new drugs against both diseases are urgently needed. OBJECTIVE: Recently, we reported the synthesis and antiprotozoal activities of a number of new 2- substituted 4-carbamoyl- and 4-aminoquinolines. This study focussed on the synthesis of novel tetrazole derivatives which are linked to the quinoline core via a piperidine ring. METHODS: Novel compounds exhibiting a 7-chloroquinoline and a tetrazole ring were prepared via Ugi-azide reaction. Modifications were restricted to the orientation and the substitution of the linker. Compounds were tested for their activities against Trypanosoma brucei rhodesiense (STIB 900). Their antiplasmodial activities were determined against a sensitive (NF54) and a multiresistant strain (K1) of Plasmodium falciparum. RESULTS: Eighteen tetrazole derivatives were prepared. The results of the biological tests were compared with the activities of drugs in use and structure-activity relationships were discussed. Their antitrypanosomal activities were only moderate. In contrast some of the compounds showed promising activity against both strains of Plasmodium falciparum and good to excellent resistance indices. CONCLUSION: The antiplasmodial activities depended on the orientation of the 4-aminopiperidine linker. Compounds with a tertiary amino group in position 4 of the quinoline ring exhibited equal activity against both strains, whereas those with a secondary amino group were mainly active against the sensitive strain.

Synthesis of new 1-benzyl tetrahydropyridinylidene ammonium salts and their antimicrobial and anticellular activities.

A series of N-benzyl tetrahydropiperidinylidene pyrrolidinium salts have been synthesized and investigated for their antiplasmodial and antitrypanosomal activities as well as for their cytotoxic effects. The antibacterial, antimycobacterial and anticancer potencies of selected compounds were examined, too. Physicochemical parameters were calculated and structure-activity-relationships are discussed.

New derivatives of quinoline-4-carboxylic acid with antiplasmodial activity.

New analogues of the recently published compound DDD107498 were prepared. Their activities were examined in vitro against the chloroquine-sensitive NF54 strain. The most active were also tested against the multiresistant K1 strain of Plasmodium falciparum. A couple of the newly synthesized compounds showed promising antiplasmodial activity and selectivity. A single compound showed adequate reduction of parasitaemia (98.1%) in mice infected with Plasmodium berghei. Survival time was doubled compared to control. The results of the biological tests of the novel compounds were compared with the activities of drugs in use. Structure-activity relationships were discussed.

New derivatives of 7-chloroquinolin-4-amine with antiprotozoal activity.

Novel ω-aminoacyl and -alkyl derivatives of 7-chloroquinolin-4-amine were prepared and their structures confirmed by NMR spectroscopy. Their antiprotozoal activities were examined in vitro against the sensitive NF54 strain as well as against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). The results were compared with the activities of clinically used drugs. Their antitrypanosomal activities were only moderate whereas their antiplasmodial activities looked very promising. Some were equal or slightly more active than chloroquine against the sensitive strain. However, in comparison to chloroquine, the activity of the new compounds was decreased much less in the resistant strain. Several possessed activity against both strains in low nanomolar concentration.

The antiprotozoal potencies of newly prepared 3-azabicyclo[3.2.2]nonanes.

3-Azabicyclo[3.2.2]nonanes are already reported as antiprotozoal agents. Structural variations were performed by attachment of several basic side chains, being part of drugs in use, to the ring nitrogen. The structures of the new compounds were established using one and two dimensional NMR measurements. All compounds were investigated for their antiplasmodial and antitrypanosomal activities against Plasmodium falciparum K 1 (multiresistant) and Trypanosoma brucei rhodesiense. Their cytotoxicity was assessed against L6 cells. The results are compared to the activities of formerly synthesized compounds. Structure-activity relationships are discussed.

Antiprotozoal activity of bicycles featuring a dimethylamino group at their bridgehead.

Several dimethylamino-derivatives of the new compound-class 3-azabicyclo[3.2.2]nonanes were prepared. For better comparison of activity also a few analogues of bicyclo[2.2.2]octanes and 2-azabicyclo[3.2.2]nonanes were synthesized. Their activities were examined in vitro against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). A couple of the newly synthesized compounds showed promising antiprotozoal activity and selectivity. The results of the biological tests of the novel compounds were compared with the activities of already synthesized compounds and of drugs in use. Structure-activity relationships were discussed.

Synthesis of new 4-phenylpyrimidine-2(1H)-thiones and their potency to inhibit COX-1 and COX-2.

Several new 4-phenylpyrimidine-2(1H)-thiones have been prepared and investigated for their potencies to inhibit COX-1 and COX-2 enzymes, and COX-2 expression in THP-1 cells. Structure-activity-relationships and physicochemical parameters are discussed. Pharmacophore screening and docking studies were carried out for the most active compound.

Synthesis of 3-azabicyclo[3.2.2]nonanes and their antiprotozoal activities.

Several bicyclic compounds, 3-azabicyclo[3.2.2]nonanes, have been prepared. The new compounds were tested for their activities against one strain of the causative organism of Malaria tropica, Plasmodium falciparum K1, which is resistant against chloroquine and pyrimethamine. In addition, their cytotoxicity and their activity against the pathogen of the East African form of sleeping sickness, Trypanosoma brucei rhodesiense, were investigated. Structure-activity relationships are discussed considering data of readily prepared compounds. For the first time, a distinct in vivo activity was observed against Plasmodium berghei in a mouse model. The active compound was further investigated.

Synthesis and antiprotozoal activities of new 3-azabicyclo[3.2.2]nonanes.

Some antimalarial agents in use typically bear basic side chains as ligands. Such ligands were attached to the amino substituent of a bridgehead atom of already antiprotozoal active 3-azabicyclo[3.2.2]nonanes. Structure verification was done by NMR measurements. The new compounds were tested for their antiplasmodial and antitrypanosomal activities against Plasmodium falciparum K 1 (multiresistant) and Trypanosoma brucei rhodesiense as well as for their cytotoxicity against L6 cells. Their activities are compared to those of already prepared compounds and structure-activity relationships are discussed.

3ß-Hydroxy-28-norolea-12,17-dien-11-one.

The title compound, C29H44O2, was formed by treatment of 11-oxooleanolic acid under strong alkaline conditions. The absolute structure of the chiral mol-ecules could not be determined reliably from the diffraction data, but is known from other triterpenes. The asymmetric unit consists of two mol-ecules, 1 and 2. In both mol-ecules, rings A and B show chair conformations. The other rings show mixed forms between envelope and half-chair conformations with atoms in positions 8, 15 and 21 forming the flaps in rings C, D and E, respectively. Rings D and E of mol-ecule 2 are disordered over two orientations, with occupancies of 0.557 (4) and 0.443 (4), which differ in the direction of the flap in ring E. In the crystal, mol-ecules 1, as well as the mol-ecules 2, are linked by O-H⋯O hydrogen bonds, forming chains parallel to the b axis.

Antiprotozoal activity of bicyclic diamines with a N-methylpiperazinyl group at the bridgehead atom.

ω-Aminoacyl and -alkyl derivatives of 4-(4-methylpiperazin-1-yl)bicyclo[2.2.2]octan-2-amines and of 5-(4-methylpiperazin-1-yl)-2-azabicyclo[3.2.2]nonanes were prepared and their activities were examined in vitro against the multiresistant K1 strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900). Some of the newly synthesized compounds showed very promising antiprotozoal activity and selectivity. A few of the alkylamino-2-azabicyclo[3.2.2]nonanes exhibited high antiplasmodial activity, whereas a single bicyclo[2.2.2]octane derivative was the most potent antitrypanosomal compound. The results of the newly synthesized compounds were compared with the activities of already synthesized compounds and of drugs in use. Structure-activity relationships were discussed.

New N-methylpiperazinyl derivatives of bicyclic antiprotozoal compounds.

The 4-methylpiperazinyl group was inserted as substituent at the bridgehead of bicyclic compounds or as terminal group of their aminoacyl and aminoalkyl side chains. The new compounds were tested in vitro for their activities against the multidrug-resistant K(1) strain of Plasmodium falciparum and Trypanosoma brucei rhodesiense (STIB 900). The results were compared to those of formerly prepared analogues and of drugs in use. A couple of bicyclo-octyl ω-(4-piperazin-1-yl)alkanoates showed high antitrypanosomal (IC(50)≤0.087µM) and antiplasmodial activity (IC(50)≤0.06µM). The most active ω-(4-methylpiperazin-1-yl)alkyl-2-azabicyclo-nonane possessed higher antiplasmodial activity (IC(50)≤0.023µM) and selectivity (S.I.=IC(50) (Cytotox.)/IC(50) (P. falciparum)=2188) than the antimalarial drug chloroquine (IC(50)=0.15µM, S.I.=1257).

Dialkylaminoalkyl derivatives of bicyclic compounds with antiplasmodial activity.

Dialkylaminoalkyl derivatives of 2-azabicyclo[3.2.2]nonanes and of bicyclo[2.2.2]octanes were prepared and their activities determined in vitro against the multiresistant K1 strain of Plasmodium falciparum. Several of the new compounds exhibited very promising antiplasmodial activity and selectivity. The results were compared to those of formerly synthesized analogues and of drugs in use. Structure-activity relationships were detected. Some of the more potent compounds were tested in vivo against Plasmodium berghei showing weak to moderate activity. A single compound was able to increase the mean survival days of infected mice.

Alkyl and dialkylaminoethyl derivatives of 5-amino-2-azabicyclo[3.2.2]nonanes and their antiplasmodial and antitrypanosomal activities.

N-Alkyl and N-(2-dialkylaminoethyl) derivatives of 5-amino-2-azabicyclo-nonanes were prepared and tested in vitro for their activities against the multidrug-resistant K1 strain of Plasmodium falciparum and Trypanosoma brucei rhodesiense (STIB 900). Most of the new compounds showed lower antitrypanosomal activity than their parent compounds. With respect to their activity against P. falciparum the N-alkyl derivatives exhibited worse selectivity due to decreased antiplasmodial activity or higher cytotoxicity. In comparison all of the new N-(2-dialkylaminoethyl) analogues possessed a much better selectivity and a single of these compounds showed even better antiplasmodial activity and selectivity than chloroquine.

Antiplasmodial and antitrypanosomal activity of bicyclic amides and esters of dialkylamino acids.

Several bicyclic amides and esters of dialkylamino acids were prepared. Their activities against a multiresistant strain of Plasmodium falciparum and against Trypanosoma brucei rhodesiense (STIB 900) were examined. Structure-activity relationships were discussed. Particularly the ester compounds showed good antiplasmodial and antitrypanosomal activity and a single compound was tested in vivo against Plasmodium berghei.

Antiplasmodial and antitrypanosomal activities of aminobicyclo[2.2.2]octyl omega-aminoalkanoates.

Several 4-aminobicyclo[2.2.2]octyl esters of omega-dialkylamino acids were prepared. Their activities against the multidrug-resistant K(1) strain of Plasmodium falciparum and Trypanosoma brucei rhodesiense (STIB 900) were determined using microplate assays and compared to those of formerly prepared analogues. The biological activity was influenced by the relative configuration in ring position 2, by the chain length of the acid moiety and by the amino substitution. The most active antiplasmodial ester was as active as chloroquine. One of the new compounds exhibited the highest antitrypanosomal activity and selectivity of all bicyclo-octane derivatives prepared so far.

Antimycobacterial and H1-antihistaminic activity of 2-substituted piperidine derivatives.

2-Substituted derivatives of the antihistaminic agents Bamipine, Diphenylpyraline and of their 1-phenyl analogues were tested for their antimycobacterial and H(1)-antagonistic activities. They are strong H1-receptor antagonists and also inhibit the growth of mycobacterials with a maximum MIC of 6.25 microg/mL against Mycobacterium tuberculosis H(37)Rv. H1-receptor antagonistic potency was slightly decreased by substitution in ring position 2 and distinctly diminished by N-aryl substitution. The antimycobacterial potency of Diphenylpyraline was in general increased by substitution in ring position 2, whereas only a few Bamipine derivatives showed markedly improved activity. A correlation between the two activities was not detected for those compounds.

Antimycobacterial activity of diphenylpyraline derivatives.

2-Substituted derivatives of diphenylpyraline and their 1-phenyl and 1-phenethyl analogues have been prepared in several steps from dihydropyridine-2(1H)-thiones. The structures of all new compounds have been confirmed by NMR spectroscopy. Their activity against Mycobacterium tuberculosis H(37)Rv as well as their cytotoxicity against human cells (HEK-293) have been determined via in vitro assays. The antimycobacterial potency was in general increased by substitution in ring position 2. The most promising modifications were a 2-isopropyl derivative and a 1,2-diphenyl analogue.