Biomedical subjects
Publications and source records attributed to Reto Brun.
Thirty weak base 1,2,4-dispiro trioxolanes (secondary ozonides) were synthesized. Amino amide trioxolanes had the best combination of antimalarial and biopharmaceutical properties. Guanidine, aminoxy, and amino acid trioxolanes had poor antimalarial activity. Lipophilic trioxolanes were less stable metabolically than their more polar counterparts.
The isolation and structural elucidation of three novel-type naphthylisoquinoline alkaloids, ancistrocladinium A and B (the latter along with its atropisomer), from a Congolese Ancistrocladus species collected in the habitat Yeteto is reported. Their structures, including all stereochemical features, were elucidated by spectroscopic, chemical, and chiroptical methods. Ancistrocladinium A and B are the first N,C-coupled naphthyldihydroisoquinoline alkaloids found in nature, i.e., with an iminium-aryl axis. Although ancistrocladinium A, which is N,8'-coupled, is configurationally stable at this axis, ancistrocladinum B and its rotational isomer are based on a hitherto unprecedented N,6'-coupling type, with a slow rotation about the hetero biaryl axis at room temperature; they thus occur as a 46:54 mixture of two configurationally semistable atropo-diastereomers. For the isomerization of (P)-ancistrocladinium B to its (M)-diastereomer and for the opposite direction, the Gibbs free energies of activation were determined to be DeltaG double dagger1 = 105.8 kJ mol-1 and DeltaG double dagger2 = 105.7 kJ mol-1, respectively. In addition, the compounds were shown to have promising antileishmanial activities.
A series of bis-2,5-[4-guanidinophenyl]thiophenes were prepared in a five step process starting from 2,5-bis[trimethylstannyl]thiophene. The compounds were evaluated in vitro against Trypanosoma brucei rhodesiense (T. b. r.), Plasmodium falciparum (P. f.), Leshmania donovani (L. d.) and Trypanasoma cruzi (T. c.), and in vivo against T. b. r. Certain compounds show promising in vitro activity against T. b. r. and P. f. and have superior in vivo activity against T. b. r. to that of pentamidine and furamidine.
In order to overcome the problem of drug resistance in malaria, it appears wise to concentrate drug discovery efforts toward new structural classes and new mechanisms of action. We report our results, targeting Plasmepsin II, a Plasmodium falciparum aspartic protease active in hemoglobin degradation, a parasite specific catabolic pathway. The results show that the new structural class is not only inhibiting PMII in vitro but is also active in a P. falciparum infected human red blood cell assay.
Selected members of three classes of rhodacyanine dyes, [0,0]-, [1,0]-, and [0,0,0]-rhodacyanines, were synthesized and their in vitro antimalarial activities against Plasmodium falciparum K1 (chloroquine-resistant strain) as well as their in vivo activities against P. berghei in mice were determined. The novel [0,0,0]-rhodacynines, 3e and 3h, possessing a benzothiazole moiety, were shown to have highly promising antimalarial activities in vivo. Moreover, the [0,0,0]-rhodacyanines were found to be orally bioavailable.
Diamidines 10a-g and 18a,b were obtained from dinitriles 9a-g and 15a,b by treatment with lithium trimethylsilylamide or upon hydrogenation of bis-O-acetoxyamidoximes. Dinitriles 9a-g were prepared via Suzuki reactions between arylboronic acids and arylnitriles. Potential prodrugs 12a-f and 17 were prepared via methylation of the diamidoximes 11a-f and 16a. Significant DNA affinities for rigid-rod molecules were observed. Compounds 10a, 10b, 10d, 18a, and 18b show IC50 values of 5 nM or less against Trypanosoma brucei rhodesiense (T. b. r.) and 10a, 10b, 10e, 18a, and 18b gave similar ones against Plasmodium falciparum (P.f.). The dications, 10a, 10d, 10f, and 10g are more active than furamidine in vivo. The prodrugs are only moderately effective on oral administration. Mouse liver microsome bioconversion of the methamidoxime prodrugs is significantly reduced from that of pafuramidine and suggests that the in vivo efficacy of these prodrugs is, in part, due to poor bioconversion.
With an aim to identify a dispiro-1,2,4-trioxolane with high oral activity and good physicochemical properties, 27 derivatives of an achiral piperidine trioxolane were synthesized; most were potent antimalarial peroxides with IC(50)s ranging from 0.20 to 7.0 ng/mL. The oral efficacies of two of these were superior to artesunate and comparable to artemether. The attractive chemical simplicity of these compounds is balanced only by an apparent metabolic susceptibility.
Chemical investigation of the roots of Diospyros assimilis had led to the isolation and characterization of six naphthalene derivatives, two 2-naphthaldehyes, namely 4-hydroxy-3,5-dimethoxy-2-naphthaldehyde 1, 4-hydroxy-5-methoxy-2-naphthaldehye 2, its related isomer 5-hydroxy-4-methoxy-2-naphthaldehyde 3 and three commonly occurring naphthoquinones, diospyrin 4, 8'-hydroxyisodiospyrin 5 and the simple monomer, plumbagin 6. Their chemical structures were established by detailed NMR investigations including 1H and 13C NMR, HSQC, HMBC and NOESY experiments. In addition, the naphthalene derivatives 1-5 were evaluated for their in vitro antiprotozoal activity against protozoan parasites belonging to the genera Trypanosoma, Leishmania and Plasmodium. Among the tested compounds, naphthaldehyde 1 showed moderate inhibition of the growth of the parasites, T. brucei, T. cruzi, L. donovani with IC50 values of 19.82, 12.28 and 38.78 microM and displayed cytotoxicity towards rat skeletal myoblasts (L-6 cells) with IC50 of 174.94 microM, while 2 and 3 were found to be comparatively less active to 1. The dimeric quinones 4 and 5 exhibited good activity against T. brucei and L. donovani with IC50 of 1.12 and 8.82 microM and 12.94 and 16.66 microM respectively.
A series of naphthalene analogues of highly active benzimidazole diamidines were synthesized using sequential Stille and Suzuki coupling reactions for preparation of the bis-nitrile intermediates. All of the diamidines showed strong DNA affinities as judged by high DeltaTm values with poly(dA-dT). The dicationic compounds were quite active in vitro versus Trypanosoma brucei rhodesiense (T. b. r.) exhibiting IC50 values ranging from 4 to 98 nM. These compounds were also active versus Plasmodium falciparum (P. f.) giving IC50 values ranging from 4 to 33 nM. Two of the compounds showed good activity in vivo in the STIB900 model for acute African trypanosomiasis; one gave 3/4 cures and the other gave 4/4 cures on ip dosage of 20 mg/kg for 4 days. The amidoxime prodrugs of the naphthalene analogues were essentially ineffective.
The in vitro activity of newly synthesized bis-(chlorophenyl)-azabicyclo[3.2.2]nonanes and bis-(chlorophenyl)-bicyclo[2.2.2]octanes against Plasmodium falciparum K(1) (resistant to chloroquine and pyrimethamine) and Trypanosoma brucei rhodesiense was investigated. Especially the bis-(chlorophenyl)-azabicyclo[3.2.2]nonanes exhibit promising antitrypanosomal activity and were tested in vivo against Trypanosoma brucei brucei featuring moderate activities.
Several aza-fused rhodacyanines were synthesized and assessed for their in vitro and in vivo antimalarial activities against Plasmodium falciparum K1 and P. berghei. All synthetic compounds showed strong selective antimalarial in vitro activity. Class II azarhodacyanines, 3, consisting of four heterocyclic units, were found to display good parasitemia suppression and low acute toxicity in vivo. Among them, 3c appeared to be the most effective at a dose of 20-25 mg kg(-1) day(-1) (ip).
We report the discovery of novel uracil-based acyclic compounds as inhibitors of deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase), an enzyme involved in nucleotide metabolism that has been identified as a promising target for the development of antimalarial drugs. Compounds were assayed against both P.falciparum dUTPase and intact parasites. A good correlation was observed between enzyme inhibition and cellular assays. Acyclic uracil derivatives were identified that showed greater or similar potency and in general increased selectivity compared to previously reported inhibitors. The most active compound reported here against the P. falciparum enzyme had a K(i) of 0.2 microM. Molecular modeling studies provided a good rationale for the observed activities. Preliminary ADME studies indicated that some of the lead compounds are drug-like molecules. These compounds are useful tools for further investigating P. falciparum dUTPase for the development of much-needed novel antimalarial drugs.
There have been major advances in the formulation of cryomedia for spermatozoa owing to their economic importance. In this study, the suitability of the commercial cryomedium Triladyl developed for bull semen was evaluated for the cryopreservation of Trypanosoma brucei gambiense. Cryopreservation efficacy was determined by direct counting of motile trypanosomes and by viability assessment using in vitro and in vivo methods. Culture medium containing 10% glycerol was used as the control. Trypanosomes cryopreserved in Triladyl demonstrated a higher in vitro viability than those in culture medium with 10% glycerol. Similar results were obtained in vivo in immunosuppressed Mastomys natalensis. Trypanosomes cryopreserved in Triladyl showed better growth characteristics than those in culture medium with glycerol. It can be concluded that the use of Triladyl in the cryopreservation of T. b. gambiense leads to a better survival of the trypanosomes which could lead to an improved isolation of T. b. gambiense from sleeping sickness patients.
A new antitrypanosomal hit compound that cures an acute (STIB 900) mouse model of Trypanosoma brucei rhodesiense trypanosomiasis is described. This bis(2-aminoimidazolinium) dicationic compound proved to be an excellent DNA minor groove binder, suggesting a possible mechanism for its trypanocidal activity. From these studies, the 4,4'-diaminodiphenylamine skeleton emerged as a good scaffold for antitrypanosomal drugs.
Based on the structures of several lipophilic trioxolane antimalarial prototypes, we set out to determine which functional groups were associated with good antimalarial profiles and identify more polar (lower LogP/LogD) lead compounds with good physicochemical properties. More lipophilic trioxolanes tended to have better oral activities than their more polar counterparts. Trioxolanes with a wide range of neutral and basic, but not acidic, functional groups had good antimalarial profiles.
After the discovery of a potent natural flavonoid glucoside as a potent inhibitor of FabI, a large flavonoid library was screened against three important enzymes (i.e., FabG, FabZ, and FabI) involved in the fatty acid biosynthesis of P. falciparum. Although flavones with a simple hydroxylation pattern (compounds 4-9) showed moderate inhibitory activity toward the enzymes tested (IC50 10-100 microM), the more complex flavonoids (12-16) exhibited strong activity toward all three enzymes (IC50 0.5-8 microM). Isoflavonoids 26-28 showed moderate (IC50 7-30 microM) but selective activity against FabZ. The most active compounds were C-3 gallic acid esters of catechins (32, 33, 37, 38), which are strong inhibitors of all three enzymes (IC50 0.2-1.1 microM). Kinetic analysis using luteolin (12) and (-)-catechin gallate (37) as model compounds revealed that FabG was inhibited in a noncompetitive manner. FabZ was inhibited competitively, whereas both compounds behaved as tight-binding noncompetitive inhibitors of FabI. In addition, these polyphenols showed in vitro activity against chloroquine-sensitive (NF54) and -resistant (K1) P. falciparum strains in the low to submicromolar range.
OBJECTIVES: Using synchronous cultures of Plasmodium falciparum malaria, the stage sensitivity of the parasite to OZ277 (RBx-11160), the first fully synthetic antimalarial peroxide that has entered Phase II clinical trials, was investigated in vitro over a concentration range of 1 x to 100 x the IC50. Secondly, partitioning of OZ277 into P. falciparum-infected red blood cells (RBCs) and uninfected RBCs was studied in vitro by measuring its distribution between RBCs and plasma (R/P). METHODS: The effects of timed in vitro exposure (1, 6, 12 or 24 h) to OZ277 were monitored by incorporation of [3H]hypoxanthine into parasite nucleic acids and by light-microscopic analysis of parasite morphology. Partitioning studies were performed with radiolabelled [14C]OZ277. RESULTS: After 1 h of exposure to OZ277 at the highest concentration (100 x the IC50) followed by removal of the compound, the hypoxanthine assay showed that growth of mature stages of P. falciparum was reduced to below 20%. Young ring forms were slightly less sensitive (43% growth). Similar stage-specific profiles were found for the antimalarial reference compounds artemether and chloroquine. Strong inhibition (< or = 6% growth) of all parasite stages was observed when the parasites were exposed to each of the three compounds for 6 h or longer. After removal of the compounds, the parasites did not recover, indicating that the observed growth inhibitions were cytotoxic rather than cytostatic. Pyrimethamine was confirmed to be active exclusively against young schizonts. Light-microscopic analysis also demonstrated the specificity of pyrimethamine against the schizont forms and showed that OZ277, artemether and chloroquine attenuated parasite growth more rapidly than did pyrimethamine. The R/P for OZ277 was 1.5 for uninfected RBCs and up to 270 for infected RBCs. CONCLUSIONS: The present study indicates similar stage-specific profiles for OZ277 and for the more well-established antimalarial agents artemether and chloroquine. Secondly, the study describes a significant accumulation of radiolabelled OZ277 in P. falciparum-infected RBCs.
N(1)-Phenyl-3,5-dinitro-N(4),N(4)-di-n-propylsulfanilamide (1) and N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (2) show potent in vitro antimitotic activity against kinetoplastid parasites but display poor in vivo activity. Seventeen new dinitroaniline sulfonamide and eleven new benzamide analogs of these leads are reported here. Nine of the sulfonamides display in vitro IC(50) values under 500 nM against African trypanosomes, and the most active antikinetoplastid compounds also inhibit the in vitro assembly of purified leishmanial tubulin with potencies similar to that of 2. While several of the potent compounds are rapidly degraded by rat liver S9 fractions in vitro, N(1)-(3-hydroxy)phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (21) displays an IC(50) value of 260 nM against African trypanosomes in vitro and is more stable than 2 in the in vitro metabolism assay.