In vitro Evaluation of the Antileishmanial and Antischistosomal Activities of p-Coumaric Acid Prenylated Derivatives

We have evaluated eight p-coumaric acid prenylated derivatives in vitro for their antileishmanial activity against Leishmania amazonensis promastigotes and their antischistosomal activity against Schistosoma mansoni adult worms. Compound 7 ((E)-3,4-diprenyl-4-isoprenyloxycinnamic alcohol) was the most active against L. amazonensis (IC50=45.92 μM) and S. mansoni (IC50=64.25 μM). Data indicated that the number of prenyl groups, the presence of hydroxyl at C9, and a single bond between C7 and C8 are important structural features for the antileishmanial activity of p-coumaric acid prenylated derivatives.

(±)-Licarin A and its semi-synthetic derivatives: In vitro and in silico evaluation of trypanocidal and schistosomicidal activities

This paper reports the synthesis of (±)-licarin A 1, a dihydrobenzofuran neolignan, resultant of an oxidative coupling reaction of isoeugenol and horseradish peroxidase (HRP) enzyme. Following, three semi-synthetic derivatives from this compound were obtained: benzylated (±)-licarin A 2, methylated (±)-licarin A 3 and acetylated (±)-licarin A 4. After structural elucidation and assignment by Nuclear Magnetic Resonance of ¹H, ¹³C and DEPT, all compounds were evaluated in vitro against Trypomastigote forms of Trypanosoma cruzi (T. cruzi), the etiologic agent of Chagas disease, and Schistosoma mansoni (S. mansoni) worms, the etiologic agent of schistosomiasis. Compound (4) was the most active against S. mansoni adult worms, displaying worm viability reduction at 25 µM and mortality of all worms at 100 and 200 µM within 24 h. Compound 1 was the second most active, showing worm viability reduction at 50 µM and mortality of 25% and 100% of worms in 24h at concentrations of 100 and 200 µM, respectively. In addition, theoretical calculations aiming at finding molecular properties that showed the correlation for schistosomicidal and trypanocidal activities of (±)-licarin A and three of its semi-synthetic derivatives were also performed.

Synthesis and biological evaluation of novel imidazolidine derivatives as candidates to schistosomicidal agents

INTRODUCTION:

Schistosomiasis is an infectious parasitic disease caused by trematodes of the genus Schistosoma, which threatens at least 258 million people worldwide and its control is dependent on a single drug, praziquantel. The aim of this study was to evaluate the anti-Schistosoma mansoni activity in vitro of novel imidazolidine derivatives.

MATERIAL AND METHODS:

We synthesized two novel imidazolidine derivatives: (LPSF/PTS10) (Z)-1-(2-chloro-6-fluorobenzyl)-4-(4-dimethylaminobenzylidene)-5-thioxoimidazolidin-2-one and (LPSF/PTS23) (Z)-1-(2-chloro-6-fluoro-benzyl)-5-thioxo-4-(2,4,6-trimethoxy-benzylidene)-imidazolidin-2-one. The structures of two compounds were determined by spectroscopic methods. During the biological assays, parameters such as motility, oviposition, mortality and analysis by Scanning Electron Microscopy were performed.

RESULTS:

LPSF/PTS10 and LPSF/PTS23 were considered to be active in the separation of coupled pairs, mortality and to decrease the motor activity. In addition, LPSF/PTS23 induced ultrastructural alterations in worms, after 24 h of contact, causing extensive erosion over the entire body of the worms.

CONCLUSION:

The imidazolidine derivatives containing the trimetoxy and benzylidene halogens showed promising in vitro schistosomicidal activity.

Discovery of New Anti-Schistosomal Hits by Integration of QSAR-Based Virtual Screening and High Content Screening

Schistosomiasis is a debilitating neglected tropical disease, caused by flatworms of Schistosoma genus. The treatment relies on a single drug, praziquantel (PZQ), making the discovery of new compounds extremely urgent. In this work, we integrated QSAR-based virtual screening (VS) of Schistosoma mansoni thioredoxin glutathione reductase (SmTGR) inhibitors and high content screening (HCS) aiming to discover new antischistosomal agents. Initially, binary QSAR models for inhibition of SmTGR were developed and validated using the Organization for Economic Co-operation and Development (OECD) guidance. Using these models, we prioritized 29 compounds for further testing in two HCS platforms based on image analysis of assay plates. Among them, 2-[2-(3-methyl-4-nitro-5-isoxazolyl)vinyl]pyridine and 2-(benzylsulfonyl)-1,3-benzothiazole, two compounds representing new chemical scaffolds have activity against schistosomula and adult worms at low micromolar concentrations and therefore represent promising antischistosomal hits for further hit-to-lead optimization.

Oxadiazole-2-oxides may have other functional targets, in addition to SjTGR, through which they cause mortality in Schistosoma japonicum

BACKGROUND

Schistosomiasis is one of the world's major public health problems. Besides praziquantel (PZQ), there is currently no other effective treatment against schistosomiasis. The development of new antischistosomal agents to curb the emergence of PZQ resistance should be a high priority. Oxadiazole-2-oxides have been identified as potential antischistosomal reagents, with thioredoxin glutathione reductase (TGR) being one of their molecular targets.

METHODS

To develop novel treatment reagents against Schistosoma japonicum, 30 novel oxadiazole-2-oxides were synthesised and their antischistosomal activities on juvenile and adult S. japonicum were evaluated in vitro and in vivo. Their inhibitory activities against S. japonicum thioredoxin glutathione reductase (SjTGR) were also analysed.

RESULTS

Most of the oxadiazole-2-oxides showed good juvenile and adult S. japonica killing activities in vitro. However, the antischistosomal effects of these compounds were not positively correlated with either their inhibition of SjTGR, or with nitric oxide (NO) release. Compounds 4a, 4b, 7c, 13, 16 and 20 resulted in 87.7%, 83.1%, 87.1%, 84.6%, 90.8% and 69.5%, respectively, mortality in the adult worms, when used to treat infected mice at schistosomula stage. These mortality rates were similar to or higher than that of artemisinin. Furthermore, compounds 4a and 16 resulted in 66.7% and 69.4% reductions in the worm burdens, respectively, when infected mice were treated at the adult worm stage. These treatment effects were similar to PZQ. No differences in activity of the oxadiazole-2-oxides against female and male adult worms were observed. The toxicity of the oxadiazole-2-oxides on mammalian cells appeared to be similar to, or less than, that of PZQ.

CONCLUSIONS

The antischistosomal activity of the oxadiazole-2-oxides does not depend on NO production or the inhibition of SjTGR activity. There may be other functional targets of the oxadiazole-2-oxides in S. japonicum. Several of the novel oxadiazole-2-oxides synthesised in this study could be used to develop novel antischistosomal drugs and explore potential molecular targets.

[Effect of calcium cyanamid synthetic drug on Schistosoma japonicum egg morphology]

OBJECTIVE

To study the morphological change of Schistosoma japonicum eggs processed by calcium cyanamide synthetic drug, so as to provide the basis for further study of the mechanism that calcium cyanamide synthetic drug to schistosome eggs.

METHODS

The calcium cyanamide synthetic drug was added to the cattle feces containing schistosome eggs and mixed up, and then the cattle feces was stacked as original shape on the marshland. Blank controls were set at the same time. The cattle feces samples were collected and.the schistosome eggs were observed under a microscope on the 1st, 2nd, 3rd, 7th day after the experiment.

RESULTS

By the effect of calcium cyanamide synthetic drug, the color of eggs was deepening gradually, the miracidia were atrophied, and the shells of eggs were thickened. The embryonic membrane of miracidia was no longer completed 3 days later, and the miracidia were deformed severely 7 days later. The atrophy of miracidia was not obvious in the blank controls.

CONCLUSION

The schistosome miracidia and embryonic membrane can be damaged by the calcium cyanamide synthetic drug, and worse damaged with time extending.

Furofuran lignans display schistosomicidal and trypanocidal activities

Parasitic diseases continue to be a major worldwide health problem, and there is an urgent need for development of therapeutic drugs. This paper describes synthesis of dehydrodiferulic acid dilactone 1 and dehydrodisinapic acid dilactone 2 furofuran lignans by oxidative coupling of ferulic and sinapic acids, respectively. Their schistosomicidal, trypanocidal, and leishmanicidal activities were evaluated in vitro against Schistosoma mansoni adult worms, trypomastigote and amastigotes forms of Trypanosoma cruzi, and promastigote forms of Leishmania amazonensis. Compound 1 did not display significant schistosomicidal activity, but it presented potent trypanocidal activity, since it induced death of trypomastigotes and amastigotes with IC50/24h of 9.3μM and 7.3μM, respectively. Compound 2 had slight trypanocidal and schistosomicidal activities. None of the compounds were active against L. amazonensis. These results demonstrated that furofuran lignans are potentially useful for anti-parasitic drugs development and should be further investigated.

Synthesis and biological evaluation of 1,4-naphthoquinones and quinoline-5,8-diones as antimalarial and schistosomicidal agents

Improving the solubility of polysubstituted 1,4-naphthoquinone derivatives was achieved by introducing nitrogen in two different positions of the naphthoquinone core, at C-5 and at C-8 of menadione through a two-step, straightforward synthesis based on the regioselective hetero-Diels-Alder reaction. The antimalarial and the antischistosomal activities of these polysubstituted aza-1,4-naphthoquinone derivatives were evaluated and led to the selection of distinct compounds for antimalarial versus antischistosomal action. The Ag(II)-assisted oxidative radical decarboxylation of the phenyl acetic acids using AgNO(3) and ammonium peroxodisulfate was modified to generate the 3-picolinyl-menadione with improved pharmacokinetic parameters, high antimalarial effects and capacity to inhibit the formation of β-hematin.

Schistosomicidal and molluscicidal activities of aminoalkylamino substituted neo- and norneocryptolepine derivatives

CONTEXT

The cryptolepines originate from the roots of the climbing shrub Cryptolepis sanguinolenta (Lindi) Schitr(Periplocaeae) which is used in Central and West Africa in traditional medicine for the treatment of malaria.

OBJECTIVES

Evaluation for the first time of a series of chloro- and aminoalkylamino derivatives of neo- and norneocryptolepines for potential schistosomicidal and molluscicidal activities.

MATERIALS AND METHODS

A series of chloro- and aminoalkylamino substituted neo- and norneocryptolepine derivatives were synthesized. They were tested in vitro against viable Schistosoma mansoni Sambon mature worms in culturemedium with fetal serum and antibiotics and in dechlorinated water against the snail vector Biomphalaria alexandrina Ehrenberg. Active compounds were further subjected to determination of their IC50 values.

RESULTS

Results showed that six neocryptolepine and two norneocryptolepine derivatives had in vitro schistosomicidal activity on Egyptian and Puerto Rican strains of S. mansoni. The most effective derivative (2-chloro-5-methyl-N-(2-morpholin-4-ethyl)-5H-indolo[2,3b]quinoline-11-amine) has IC50 and IC90 1.26 and 4.05 μM and 3.54 and 6.83 μM with the Egyptian and Puerto Rican strains of Schistosoma, respectively. All eight derivatives showed molluscicidal activity against the vector snail B. alexandrina. The most active compound (2-chloro-11-(4-methylpiperazin-1-yl)-6H-indolo[2,3-b] quinoline) has LC50 0.6 and LC90 3.9 ppm after 24 h.

DISCUSSION AND CONCLUSIONS

The findings demonstrate that introducing chloro- and aminoalkylamino side chain initiated both schistosomicidal and molluscicidal activities in these derivatives. The structure–activity relationship of this series of compounds is discussed.

Synthesis of new praziquantel analogues: potential candidates for the treatment of schistosomiasis

An efficient synthesis of antischistosomal drug praziquantel and analogues was achieved and the synthetic route designed was to afford structurally diverse analogues for better structure-activity relationship understanding. Total of nineteen PZQ analogues with structural variations at amide, piperazine and aromatic moieties have been synthesized and fully characterized. Among all the new analogues tested for antischistosomal activity, one dimethoxy tetrahydroisoquinoline analogue and two tetrahydro-β-carboline analogues exhibited moderate activity against adult Schistosoma mansoni. Tetrahydro-β-carboline analogues showed moderate activity whereas the presence of p-trifluoromethylbenzoyl and p-toluenesulphonyl moieties resulted in complete suppression of antischistosomal activity.

In vitro and in vivo activities of synthetic trioxolanes against major human schistosome species

Schistosomiasis is a parasitic disease that remains of considerable public health significance in tropical and subtropical environments. Since the mainstay of schistosomiasis control is chemotherapy with a single drug, praziquantel, drug resistance is a concern. Here, we present new data on the antischistosomal properties of representative synthetic 1,2,4-trioxolanes (OZs). Exposure of adult Schistosoma mansoni for 24 h to a medium containing 20 mug/ml OZ209 reduced worm motor activity, induced tegumental alterations, and killed worms within 72 h. While exposure of S. mansoni to OZ78 had no apparent effect, addition of hemin reduced worm motor activity and caused tegumental damage. Administration of single 200-mg/kg of body weight oral doses of OZ78, OZ209, and OZ288 to mice harboring a juvenile S. mansoni infection resulted in worm burden reductions of 82.0 to 95.4%. In the adult infection model in mice, single 400-mg/kg doses of these compounds resulted in a maximum total worm burden reduction of 52.2%. High worm burden reductions (71.7 to 86.5%) were observed after administration of single 200-mg/kg doses of OZ78 and OZ288 to hamsters infected with either juvenile or adult S. mansoni. A single 200-mg/kg dose of OZ78 to hamsters infected with adult Schistosoma japonicum resulted in total and female worm burden reductions of 94.2 to 100%. Our results, along with the low toxicity, metabolic stability, and good pharmacokinetic properties of the OZs, indicate the potential for the development of novel broad-spectrum antischistosomal OZ drug candidates.

Design, synthesis, and in vivo evaluation of oxamniquine methacrylate and acrylamide prodrugs

Oxamniquine is an antiparasitic agent commonly used in therapeutics against Schistosoma mansoni. Although it is well tolerated, some adverse effects justify the search for new compounds with prolonged biological action, so that monomeric and polymeric oxamniquine prodrugs were designed. Synthetic results assisted by molecular modeling study showed the possibility to obtain the corresponding monomeric forms of the oxamniquine methacrylate (1) and oxamniquine acrylamide (2). Successful copolymerization procedure only occurred on the methacrylic compound, generating the oxamniquine methacrylate copolymer (3). Submitted to a preliminary in vivo biological evaluation, a similar oxamniquine profile was observed to the monomeric forms although an inadequate drug release may be responsible for the methacrylic copolymer failure.

Improvement of in vitro efficacy of a novel schistosomicidal drug by incorporation into nanoemulsions

The aim of this article included the development and evaluation of the capacity of nanoemulsions to improve the activity of the novel schistosomicidal drug-2-(butylamino)-1-phenyl-1-ethanethiosulfuric acid (BphEA). BphEA is a compound with a poor solubility in water, which makes its application as a drug difficult. Nanoemulsion formulations presenting anionic (NANOSTOA, NANOST and NANOLP) and cationic (NANOSTE) interfacial charges were prepared to encapsulate BphEA. These formulations were characterized by the encapsulation rate, diameter, and zeta potential. NANOSTOA, NANOST, and NANOLP presented an entrapment efficiency and zeta potential of 18.7+/-1.8% and -33.6+/-1.2 mV; 20.5+/-3.0% and -31.5+/-5.7 mV; as well as 33.8+/-7.2% and -62.6+/-1.3 mV, respectively. NANOSTE presented an entrapment efficiency of 51.8+/-5.0% and a zeta potential of 25.7+/-3.9 mV. The mean droplet size (between 200 and 252 nm) and polydispersity index (between 0.158 and 0.294) were similar for all formulations. The stability study showed no alteration in these formulations' zeta potential and size. The in vitro schistosomicidal activity of BphEA was higher with the use of NANOSTE than with free BphEA. In addition, release studies revealed a good stability of NANOSTE containing BphEA in a biological medium. These results indicate that cationic nanoemulsions can represent an interesting delivery system for the pharmaceutical formulation of BphEA.

Synthesis of Pyrazolo[1,5-α]pyrimidinone Regioisomers

This work describes two distinct routes to prepare pyrazolo[1,5-alpha]pyrimidin-7-ones and two distinct routes to prepare pyrazolo[1,5-alpha]pyrimidin-5-ones. Use of 1,3-dimethyluracil as the electrophile in the preparation of the pyrimidin-5-one regioisomer represents a correction of previously reported results. Also, a novel reaction to prepare this isomer was identified and the reaction mechanism elucidated. This work provides the experimentalist with complimentary synthetic pathways that afford either the pyrimidin-7-one or the pyrimidin-5-one regioisomer.

New imidazolidinic bioisosters: potential candidates for antischistosomal drugs

The emergence of strains of Schistosoma resistant to praziquantel has drawn attention to the search for new schistosomacide drugs. Imidazolidinic derivatives have performed outstandingly against adult S. mansoni worms when evaluated in vitro. The molecular modification of imidazolidine by way of bioisosteric replacement gives rise to variations in its biological response. This study verifies the potential of substituent groups in the derivatives (Z)3-benzyl-5-(2-fluoro-benzylidene)-imidazolidine-2,4-dione NE4, 3-benzyl-5-(4-chloro-arylazo)-4-thioxo-imidazolidin -2-ona PT5, 3-benzyl-5-(3-fluoro-benzylidene)-1-methyl-2-thioxo-imidazolidin-4-one JT53; 3-benzyl-1-methyl-5-(4-methyl-benzylidene)-2-thioxo-imidazolidin-4-one JT63; 3-benzyl-1-methyl-5-(4-methoxi-benzylidene)-2-thioxo -imidazolidin-4-one JT68; 3-(4-chloro-benzyl)-1-methyl-5-(4-methoxi-benzylidene)-2-thioxo-imidazolidin-4-one JT69; 3-(4-phenyl-benzyl)-1-methyl-5-(4-methoxi-benzylidene)-2-thioxo-imidazolidin-4-one JT72 by determining the viability in vitro of adult S. mansoni worms in the presence of these derivatives. The susceptibility of the worms obtained from mice and kept in culture in the presence of different concentrations was determined by way of schistosomacide kinetic, observed every 24 h over a period of eight days. The results show that the worms were more sensitive to the PT5 derivative at a concentration of 58 microM which killed 100% of the worms after 24 h of contact, also giving rise to alterations in the tegument surface of the worms with the formation of bubbles and peeling. These observations suggest a strong electronic contribution of the arylazo grouping in the biological response.

Synthesis of new 4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine derivatives with an incorporated thiazolidinone moiety and testing their possible serine protease and cercarial elastase inhibitory effects with a possible prospective to block penetration of Schistosoma mansoni cercariae into the mice skin

5-Substituted 4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine were synthesized by interaction of 4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-sulfonylhydrazide with some aldehydes to give the corresponding Schiff-bases, which after cyclization gave corresponding thiazolidinones. For some of the thiazolidinones, Mannich bases reaction was carried out. All the derivatives were tested for their possible inhibitory effect on Schistosoma mansoni cercarial elastase (CE). Only, N-(4-methylbenzyledine)-4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-sulfonylhydrazide was found to have potent inhibitory effect on the CE activity with IC50 = 264 microM. Upon its use as a paint for mice tails before infection with S. mansoni cercariae, the compound formulated in jojoba oil caused a significant reduction (93%; P-value = 0.0002) in the worm burden. IgG & IgM in mice sera were measured by using several S. mansoni antigens by ELISA. Sera from treated infected mice (TIM) 2, 4, and 6 weeks (W) post infection (PI) showed 1.2 folds lower, 1.2 folds higher, 1.7 folds lower IgM reactivity against soluble cercarial antigenic preparation (CAP), respectively, when compared with sera collected from infected untreated mice (IUM). Sera from TIM 2, 4, and 6WPI showed 1.3, 1.6, and 1.7 folds higher IgG reactivity, respectively against CAP than the IgG reactivity from IUM. Sera from TIM 2, 4 and 6WPI showed 1.5, 1.2 folds lower and 1.4 folds higher IgM reactivity, respectively against soluble worm antigenic preparation (SWAP) when compared with sera collected from IUM. Sera from TIM 2, 4, and 6WPI showed 1.4, 1 folds lower and 1 fold higher IgG reactivity, respectivley to SWAP when compared with sera from IUM. Sera from TIM 2, 4, and 6WPI had generaly lower IgM and IgG reactivities against soluble egg antigen (SEA) when compared with sera from IUM.

Synthesis and schistosomicidal activity of new substituted thioxo-imidazolidine compounds

Synthesis and physico-chemical properties of 3-benzyl-5-(4-fluoro-benzylidene)-1-methyl-2-thioxo-imidazolidin-4-ones, 5-benzylidene-3-(4-nitro-benzyl)-2-thioxo-imidazolidin-4-ones and 4-acridin-9-ylmethylene-1-benzyl-5-thioxo-imidazolidin-2-ones compounds are described. These thioxo-imidazolidine derivatives were prepared by alkylation and condensation with 4-fluoro-benzaldehyde or nucleophilic Michael addition with cyanoacrylates. The schistosomicidal activity of 3-benzyl-5-(4-fluoro-benzylidene)-1-methyl-2-thioxo-imidazolidin-4-one compounds was evaluated.

Synthesis of some new benzothiazole derivatives as potential antimicrobial and antiparasitic agents

Several thiazolidinonyl benzothiazoles 8a-b and thiazolinylbenzothiazoles 9a-j were synthesized by the reaction of 2-(N-substituted thiocarbamoyl hydrazino) benzothiazoles 7a-d with chloroacetic acid or phenacyl bromide respectively. The intermediate compounds 7a-d were prepared in a good yield by the reaction of 2-hydrazinobenzothiazole (6) with phenylisothiocyanates. Synthesis of hydrazones 10a-c were performed by the reaction of 6 with the corresponding aldehydes. Trials to cyclize the obtained hydrazones 10a-c into the corresponding triazolo derivatives 11a-c were unsuccessful. Addition of 4-morphylino carbonyl chloride to compound 6 yielded the corresponding 2-acid hydrazide derivative 12. Some of the prepared compounds were screened for their anti-parasitic activity. Most of them showed reasonable antinematodal or schistosomicidal activity. In addition, antimicrobial screening of all of the prepared new compounds was performed against Staphylococcus aeurus ATCC 6538, Escherichia coli ATCC 8735 and Candida albicans ATCC 10321 but non of them was active.

Synthesis of a new antischistosomally active and toxicologically tolerant C-12 monothione surrogate of the universal antihelmintic praziquantel

A new C-12 monothione mimic (III) of the universal antihelmintic Praziquantel (I) namely, 2-cyclohexylthiocarbonyl( 1,2.3,6,7,11b)-hexahydro-4H-pyrazino[2-1a] isoquinoline-4-one was chemically synthesized and structurally elucidated (Elemental analysis. El-Mass, 13C-NMR and IR spectroscopy). Antischistosomal potency in the order of -76% comparable to that for our newly reported C-12 and C-4 dithion mimic II (-70%) and Praziquantel. Praziquantel (100%, mice infected with S. mansoni cercariae), was realized. Toxicological evaluation (mice liver and kidney functions) and biochemical parameters (cholesterol, triglycerides, albumin, total serum proteins and amino acid profile of liver protein homogenate) were also assayed. Comparable to the parent drug, general insignificant toxicological diferences could be attributed for III. Interestingly, III exhibited intermediate biological figures between I and II. An order of II<III<I with respect to the antischistosomal potency and II>III>I, for the other tested biochemical parameters was observed. A consideration of obtained results could indicate that, structurally, an intact glycine amide segment of the pyrazine moiety, as it is the case in both I and III, and not in II (glycine thioamide) seemed now more crucial for exhibiting an optimum antihelmintic potency as well as a more tolerant toxicity characteristics. Additionally, the obtained comparable amino acid profile of mice liver protein homogenate after the treatment by III, could suggest similar biochemical, lethal mechanistic and metabolic routes for II, III and I. The new lipophilic candidatee III seems to merit more profound chemical, biological, and pharmaceutical investigations.

Synthesis and evaluation of new oxamniquine derivatives

Oxamniquine derivatives were synthesized and evaluated as novel schistosomicide agents. Oxamniquine (1,2,3,4-tetrahydro-2-[[(1-methylethyl)amino]methyl]-7-nitro-6-quinolinemethanol) was submitted to the Mannich reaction, using formaldehyde, paraformaldehyde and acetaldehyde as reagents, and gave three unexpected products: two of them were cyclized on the alkylamine side chain and another etherified on the aminequinolinemethanol group. The three compounds were biologically evaluated using mice infected with Schistosoma mansoni and showed promising activities, but had higher toxicities. For studies on structure-activity relationships, results demonstrate that the side alkylamine group can be modified with preserved activity, but that this modification is associated with increased toxicity.

6-Aminopyridine-3-thiol

The title compound, C(5)H(6)N(2)S, is a simple but novel pyridinethiol of pharmacological interest. The molecule is planar. The crystal packing is dominated by hydrophobic contacts and a pair of hydrogen-bond interactions between the amino group of one pyridine molecule and the ring N atom of a neighbouring base, stabilizing the structure.

Synthetic and bioorganic investigations of 2-cyclohexylthiocarbonyl( 1,2,3,6,7,11B)hexahydro-4H-pyrazino [2-1a] isoquinoline-4-thione, a new dithione mimic of the universal anthelminthic Praziquantel

As a continuation for our previous approaches to establish structure-antischistosomal activity relationship (SAR) among some new rationally synthesized analogues of praziquantel, herein a new C-4 and C-12 dithione mimic of the drug namely, 2-cyclohexylthiocarbonyl (1, 2, 3, 6, 7, 11b) hexahydro-4H-pyrazino[2-la]isoquinoline-4-thione (II) was synthesized and antischistosomally investigated (mice infected with S. masoni cercariae). Further, some significant biochemical and toxicological parameters for both the control and the dithione II treated mice, particularly the total serum and liver proteins, liver enzymes, serum total lipids, cholesterol, triglycerides, albumin, globulins and creatinine, were assayed. The determined induced amino acid profile of liver protein hydrolysate could indicate a close similarity of the working biological mechanism for both I and II. Comparable to praziquantel, the dithione II was found, still promisingly antischistosomally active (approximately 70% of I, collective average activity, based on 500 mg II/kg mouse body weight). Equally, generally tolerant toxicity parameters for liver and kidney functions could be attributed. Due to the still absence of quasi-potent praziquantel candidates since its discovery (1975), the dithione II could be considered as an interesting anthelminthic candidate susceptible for further profound studies and structure modulations. In this context, some perspectives were also suggested.

Synthesis and study of the antischistosomal potency and induced biological parameters of a new 2-palmitoyl analogue of the universal antihelminthic praziquantel

2-Palmitoyl[1,2,3,6,7,11b]hexahydro-4H-pyrazino[2-la]isoquinoline-4-one [III] a highly lipophilic analogue of the universal antihelminthic PRAZIQUANTEL [I] was rationally multi-stepwise synthesized and antischistosomally and biochemically screened. The 2-palmitoyl conjugation was hypothesized to be an antischistosomal adjuvant (Tween 40 mimicry), to the reported crucial pyrazino-isoquinoline moiety. On a constant weight doses bases of I and III (500 mg/kg mouse body weight), the activity of III was found to be approximately 70% of I (mice infected with S. mansoni cercariae) and with satisfactory toxicological and biochemical profile (mice liver and kidney functions). Equivalent molar weight assay (M 1:1.4 for I and III, respectively), which could further plead in favour of the potency of III, was not yet tested. The analogue III, which favourable incorporates the human metabolically and physiologically compatible, palmitic acid segment, seems to be an antischistosomally promising candidate for more integrated studies.

Synthesis and antischistosomal activity of a new 2-nicotinoyl dipeptide analogue of praziquantel

As an approach to a structure-antischistosomal activity-relationship with possible pharmacological potentiation of the anthelmintic drug praziquantel, a new dipeptide analogue, namely, N alpha-nicotinoyl-L-aspartyl-beta-(1,2,3,6,7,11b-hexahydro-4H-pyrazino[2- 1a]isoquinoline-4-one)-L-phenylalanine methyl ester, was synthesized and antischistosomally investigated in mice infected with S. mansoni cercariae. Parallely, its simple 2-nicotinoyl analogue was synthesized and tested. Both compounds were less, but still, interestingly active (approximately 63 and approximately 66%, respectively) compared to praziquantel (approximately 90%).

Studies on some derivatives of oxamniquine

On the basis of the remarkable biological similarities between hycanthone and oxamniquine and as a sequel to our finding that some esters of hycanthone are active against hycanthone-resistant schistosomes, we prepared oxamniquine acetate, oxamniquine N-methylcarbamate, and four substituted phenylsulfonohydrazones of oxamniquine aldehyde. These compounds were tested for their effect on survival of and on [3H]uridine incorporation into hycanthone-sensitive and -resistant Schistosoma mansoni. All of these derivatives were effective to a greater or lesser degree in killing worms and in inhibiting [3H]uridine incorporation in the sensitive strain, but none was effective in the resistant strain.

Preparation and antischistosomal and antitumor activity of hycanthone and some of its congeners. Evidence for the mode of action of hycanthone

The synthesis of a series of esters of hycanthone (HC) and 7-hydroxyhycanthone, their antitumor activity, and their antischistosomal effects on HC-sensitive and HC-resistant schistosomes are reported. Binding studies using tritium-labeled HC and hycanthone N-methylcarbamate (HNMC) with calf thymus DNA provided evidence that HNMC but not HC alkylated the DNA. Tritiated HNMC also bound to the DNA of intact HeLa cells exposed to the drug while very little tritiated HC bound to DNA under the same conditions. The mechanism proposed previously to account for the antischistosomal action of HC, namely, drug esterification followed by alkylation of DNA, applies also to the antitumor action of the drug as shown in Scheme I.

[Preparation and schistosomicidal activity of vinylogues of 1,3-dithio-3-thione]

The synthesis of vinylogues of 1,2-dithiol-3-thione is described. The activity in experimental schistosomiasis (schistosomicidal activity and, for the most interesting ones, on the egg-laying) was tested in mice with Schistosoma mansoni in comparison with oltipraz.

5-(Hydroxyimino)-4-methoxy-2-(pivaloylimino)thiazolidine-3 -acetamide, a reduced nitroheterocyclic derivative with potent schistosomicidal properties

The synthesis and antischistosome properties of 5-(hydroxyimino)-4-methoxy-2-(pivaloylimino)thiazolidine-3- acetamide (1) are described. The compound was prepared by reduction of the nitrothiazoline (2) with stannous chloride in methanol, and represents the first example of a reduced nitroheterocyclic compound showing potent schistosomicidal properties. The possible relationship of compounds such as 1 to the as yet unidentified reduced active but toxic entities formed in vivo from nitroheterocyclics like metronidazole is discussed.

Synthesis of new 8-(5-substituted amino-1,3,4-oxadiazol-2-yl) and 8-(5-substituted amino-1,3,4-thiadiazol-2-yl) methoxyquinolines with antibilharzial activity

Several 5-substituted amino-1,3,4-oxadiazol-2-yl and 5-substituted amino-1,3,4-thiadiazol-2-yl derivatives with different 8-hydroxyquinoline moieties in the 2-position were prepared and tested for their antiparasitic activity. Preliminary biological tests on mice experimentally infested with Schistosoma mansoni revealed that the new compounds show moderate schistosomicidal activity.

9-acridinyl and 2-methoxy-6-chloro-9-acridinyl derivatives of aliphatic di-, tri-, and tetraamines. Chemistry, cytostatic activity, and schistosomicidal activity

9-acridinyl derivatives of 1,6-hexanediamine, 1,8-octanediamine, bis(3-aminopropyl)amine, N,N'-bis(3-amino-propyl)piperazine, and N-ethyl-1,6-hexanediamine in the form of their hydrochlorides were prepared in high yields and converted into potential hetero bis DNA intercalating diacridines. The corresponding potential homo bis DNA intercalating reagents were prepared by heating the above amines with 9-chloroacridines. The chemical stability of the acridines was examined. Their cytostatic activity against Cloudman melanoma cells, in vitro, has been determined. The strongest cytostatic activity was observed for the acridine derivatives of the tri- and tetraamines. The schistosomicidal activity of selected acridine and diacridine derivatives against Schistosoma mansoni in mice was found to be insignificant. The S. mansoni egg development was apparently suppressed by this treatment.