Structure-Activity Relationships and Antiplasmodial Potencies of Novel 3,4-Disubstituted 1,2,5-Oxadiazoles

The 4-substituted 3-amino-1,2,5-oxadiazole 1 from the Malaria Box Project of the Medicines for Malaria Venture foundation shows very promising selectivity and in vitro activity against Plasmodium falciparum. Within the first series of new compounds, various 3-acylamino analogs were prepared. This paper now focuses on the investigation of the importance of the aromatic substituent in ring position 4. A number of new structure-activity relationships were elaborated, showing that antiplasmodial activity and selectivity strongly depend on the substitution pattern of the 4-phenyl moiety. In addition, physicochemical parameters relevant for drug development were calculated (logP and ligand efficiency) or determined experimentally (CYP3A4-inhibition and aqueous solubility). N-[4-(3-ethoxy-4-methoxyphenyl)-1,2,5-oxadiazol-3-yl]-3-methylbenzamide 51 showed high in vitro activity against the chloroquine-sensitive strain NF54 of P. falciparum (PfNF54 IC50 = 0.034 µM), resulting in a very promising selectivity index of 1526.

8-Amino-6-Methoxyquinoline-Tetrazole Hybrids: Impact of Linkers on Antiplasmodial Activity

A new series of compounds was prepared from 6-methoxyquinolin-8-amine or its N-(2-aminoethyl) analogue via Ugi-azide reaction. Their linkers between the quinoline and the tert-butyltetrazole moieties differ in chain length, basicity and substitution. Compounds were tested for their antiplasmodial activity against Plasmodium falciparum NF54 as well as their cytotoxicity against L-6-cells. The activity and the cytotoxicity were strongly influenced by the linker and its substitution. The most active compounds showed good activity and promising selectivity.

New Acyl Derivatives of 3-Aminofurazanes and Their Antiplasmodial Activities

An N-acylated furazan-3-amine of a Medicines for Malaria Venture (MMV) project has shown activity against different strains of Plasmodium falciparum. Seventeen new derivatives were prepared and tested in vitro for their activities against blood stages of two strains of Plasmodium falciparum. Several structure-activity relationships were revealed. The activity strongly depended on the nature of the acyl moiety. Only benzamides showed promising activity. The substitution pattern of their phenyl ring affected the activity and the cytotoxicity of compounds. In addition, physicochemical parameters were calculated (log P, log D, ligand efficiency) or determined experimentally (permeability) via a PAMPA. The N-(4-(3,4-diethoxyphenyl)-1,2,5-oxadiazol-3-yl)-3-(trifluoromethyl)benzamide possessed good physicochemical properties and showed high antiplasmodial activity against a chloroquine-sensitive strain (IC₅₀(NF54) = 0.019 µM) and even higher antiplasmodial activity against a multiresistant strain (IC₅₀(K₁) = 0.007 µM). Compared to the MMV compound, the permeability and the activity against the multiresistant strain were improved.

Preparation of new 1,3-dibenzyl tetrahydropyridinylidene ammonium salts and their antimicrobial and anticellular activities

New 1,3 dibenzyl -tetrahydropyridinylidene ammonium salts have been prepared from unsubstituted or N-benzylated tetrahydropyridinylidene ammonium salts. The antiplasmodial and antitrypanosomal activities as well as their cytotoxic effects were determined using microplate assays. In addition, their activities against two gram positive and two gram negative bacteria strains and a yeast strain were examined. Furthermore, anticancer effects against two cell lines were investigated. Physicochemical parameters were calculated and structure-activity-relationships discussed. One compound showed antiplasmodial activity against a multiresistant strain of Plasmodium falciparum in subnanomolar concentration. Antitrypanosomal activities were detected in low nanomolar concentrations. A single compound was active against grampositive and gramnegative bacteria, as well as yeast. One compound inhibited the growth of a HCT cell line in low concentration.

New 2-aminopyrimidine derivatives and their antitrypanosomal and antiplasmodial activities

Abstract

Novel 2-aminopyrimidine derivatives were prepared from acyclic starting materials, benzylidene acetones and ammonium thiocyanates, via 5 steps, including ring closure, aromatization, S-methylation, oxidation to methylsulfonyl compounds, and formation of guanidines with suitable amines. The prepared compounds differ from each other by the substitutions of their amino group and of their phenyl ring. The 2-aminopyrimidines were tested by use of microplate assays for their in vitro activities against a causative organism of sleeping sickness, Trypanosoma brucei rhodesiense, as well as against a causative organism of malaria, Plasmodium falciparum NF54. Their cytotoxic properties were determined with L-6 cells (rat skeletal myoblasts). Some of the compounds exhibited quite good antitrypanosomal activity, and others showed excellent antiplasmodial activity. The influence of the structural modifications on these activities is discussed.

Graphic abstract

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 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).