Oxamniquine

Synthetic Routes and Reaction Conditions: The synthesis of oxamniquine begins with a molecule containing a quinoline structure. The process involves several key reactions, including substitution and reduction . Initially, the starting molecule undergoes a substitution reaction activated by sodium carbonate to form an intermediate structure. This intermediate then undergoes a bimolecular nucleophilic substitution (SN2) reaction, followed by hydrogenation with nickel as a catalyst . The final steps involve nitration using concentrated nitric and sulfuric acids, followed by microbial oxidation to yield this compound .

Industrial Production Methods: Industrial production of this compound follows similar synthetic routes but on a larger scale. The process is optimized for yield and purity, ensuring that the final product meets pharmaceutical standards. The use of automated reactors and stringent quality control measures are integral to the industrial synthesis of this compound .

Types of Reactions: Oxamniquine undergoes various chemical reactions, including:

Substitution Reactions: Involving the replacement of functional groups within the molecule.

Reduction Reactions: Such as the hydrogenation step in its synthesis.

Nitration Reactions: Introduction of nitro groups using nitric and sulfuric acids.

Common Reagents and Conditions:

Sodium Carbonate: Used in the initial substitution reaction.

Nickel Catalyst: Employed in the hydrogenation step.

Nitric and Sulfuric Acids: Utilized for nitration.

Major Products Formed: The primary product formed from these reactions is this compound itself, with intermediate compounds being converted through subsequent steps .

Oxamniquine is an antihelminthic drug primarily used in the treatment of schistosomiasis, a parasitic disease caused by blood flukes (schistosomes) . It is particularly effective against Schistosoma mansoni, one of the major species responsible for this disease .

Efficacy Against Schistosomiasis

This compound has been shown to be highly effective against S. mansoni . However, its effectiveness varies depending on the specific diagnostic methods used . Stool examinations have shown high cure rates with this compound, but when more sensitive methods like quantitative oogram by rectal biopsy are used, the cure rates can drop . Praziquantel, another drug used to treat schistosomiasis, maintains high cure rates regardless of the diagnostic method used .

A study comparing this compound and praziquantel found that stool examinations showed cure rates of 90.3% for this compound and 100% for praziquantel . However, when the oogram method was used, the cure rate for this compound dropped to 42.4%, while praziquantel remained high at 96.1% .

Re-engineering this compound

Researchers have been working on re-engineering this compound to develop new treatments that can prevent drug resistance . Drug resistance occurs when the parasitic worm gains mutations and no longer responds to treatment . Derivatives of this compound have shown efficacy against all three schistosomiasis species (S. mansoni, S. haematobium, and S. japonicum) in vitro .

Structural data from collaborative studies have helped identify points that could be restructured to allow this compound to act differently in the body . This iterative process has led to the identification of derivatives that kill S. haematobium and S. japonicum .

This compound Derivatives

Several this compound derivatives have shown promising antischistosomal activity . These derivatives, including ferrocene-, ruthenocene-, and benzene-containing compounds, have demonstrated in vitro death of S. mansoni and S. haematobium adult worms . In vivo studies have shown worm burden reductions of 76 to 93% against adult S. mansoni .

Use in Conjunction with Other Drugs

Given the concerns about drug resistance, researchers are exploring the use of this compound in conjunction with other drugs like praziquantel . The goal is to design an this compound derivative that is effective against all major human schistosome species and can be used with praziquantel to combat emerging resistance and improve overall treatment efficacy .

Reduction of Morbidity

Even though this compound may not cure all patients in areas endemic for S. mansoni, its use has led to a marked reduction in disease morbidity, with a significant reduction in hepatosplenic forms of the disease in Brazil .

Rifaximin and Hepatosplenic Schistosomiasis

Oxamniquine exerts its effects by targeting the nucleic acid metabolism of Schistosoma mansoni . The drug is activated by a schistosome sulfotransferase enzyme, which converts this compound into an ester (likely acetate, phosphate, or sulfate) . This ester then dissociates, producing an electrophilic reactant capable of alkylating schistosome DNA, leading to the paralysis and death of the worms .

Comparison with Structurally Similar Compounds

Hycanthone

Hycanthone, another schistosomicide, shares mechanistic similarities with OXM, including DNA intercalation and reliance on enzymatic activation. However:

• Structural Differences: Hycanthone lacks OXM’s nitro group and isopropylaminomethyl side chain, which are critical for SULT-mediated activation .
• Resistance Profile: Both drugs face cross-resistance in S. mansoni strains with impaired SULT activity.

Table 1: Structural and Functional Comparison of OXM and Hycanthone

Dehatridine

Dehatridine, an alkaloid, exhibits schistosomicidal activity via docking to the S. mansoni Sm14 fatty-acid-binding protein. Compared to OXM:

• Docking Efficiency : Dehatridine has a lower docking score (−147.1 kcal/mol) than OXM (−86.6 kcal/mol), suggesting stronger target affinity .
• Mechanistic Overlap : Both interact with Tyr and Arg residues in target proteins, but Dehatridine’s pi-interactions may enhance stability .

Comparison with Functionally Similar Antischistosomal Agents

Praziquantel (PZQ)

PZQ, the first-line treatment for all schistosome species, contrasts with OXM in key areas:

• Spectrum of Activity: PZQ is effective against S. mansoni, S. hematobium, and S. mansoni .
• Mechanism : PZQ disrupts calcium homeostasis in parasite teguments, unlike OXM’s nucleic acid synthesis inhibition .
• Clinical Efficacy : At 40 mg/kg, PZQ achieves higher cure rates (CR) than OXM 40 mg/kg (RR = 1.09, p = 0.034) but shows comparable efficacy to OXM 50 mg/kg .

Table 2: Clinical and Pharmacokinetic Comparison of OXM and PZQ

This compound Derivatives (CIDD-0066790)

Recent derivatives address OXM’s limitations:

• Structural Modifications : Derivatives like CIDD-0066790 retain OXM’s core structure but introduce side-chain adjustments to enhance binding to ShSULT (e.g., avoiding Val-139 clashes in S. hematobium) .
• Broad-Species Efficacy : CIDD-0066790 kills S. mansoni, S. hematobium, and S. japonicum in vitro, overcoming species-specific resistance .
• Mechanistic Insights: X-ray crystallography confirms derivative binding to sulfotransferase active sites, with improved turnover rates compared to OXM .

Pharmacokinetic and Toxicity Considerations

• Metabolism : OXM is metabolized by gut-wall enzymes, reducing hepatic strain, whereas PZQ undergoes extensive hepatic first-pass metabolism .
• Toxicity: OXM exhibits hepatotoxicity (MaxNeg = 0 in similarity models), contrasting with non-hepatotoxic agents like Dextrothyroxine .

Oxamniquine (OXA) is an antischistosomal drug that has been utilized primarily for the treatment of schistosomiasis, particularly against Schistosoma mansoni. This compound has garnered attention due to its unique mechanism of action and the potential for developing derivatives that enhance its efficacy against other schistosome species.

This compound is a prodrug that requires enzymatic activation to exert its biological effects. The activation occurs through a sulfotransferase enzyme present in S. mansoni, which converts OXA into a reactive alkylating agent. This active form then binds covalently to DNA and other macromolecules within the parasite, leading to cell death. The specific enzyme responsible for this activation has been identified as SmSULT-OR, a sulfotransferase that is absent in resistant schistosome strains .

In Vitro and In Vivo Studies

Recent studies have demonstrated the biological activity of OXA and its derivatives against various schistosome species. Notably, derivatives such as Fc-CH2-OXA and Rc-CH2-OXA have shown promising results in vitro against S. mansoni and S. haematobium. The activity of these compounds was assessed by measuring their half-maximal inhibitory concentration (IC50) values, which indicate the potency of the drug.

Table 1: In Vitro Activity of this compound Derivatives

The results indicate that while OXA itself is ineffective against S. haematobium and S. japonicum, its derivatives exhibit significant activity, particularly Rc-CH2-OXA, which has a notably low IC50 value against S. haematobium .

Case Studies

A study conducted by Pasche et al. highlighted the importance of protein binding in drug efficacy. It was observed that the presence of albumin reduced the activity of OXA derivatives, emphasizing the need for further modifications to enhance bioavailability and therapeutic effectiveness . Additionally, another investigation focused on developing new derivatives through an iterative process involving soaking these compounds into sulfotransferase crystals, leading to the identification of two promising candidates: CIDD-0072229 and CIDD-149830, which demonstrated efficacy against both S. haematobium and S. japonicum .

Basic Research Questions

Q. What analytical methodologies are recommended for quantifying oxamniquine in pharmaceutical formulations and biological matrices?

A validated spectrofluorimetric method using derivatization with 1-dimethylaminonaphthalene-5-sulphonyl chloride (dansyl chloride) is widely employed. This method achieves linearity at 0.02–0.2 µg ml⁻¹, with a detection limit of 0.007 µg ml⁻¹ and quantitation limit of 0.02 µg ml⁻¹ . Key parameters include reaction at pH 10 (sodium carbonate buffer), excitation/emission wavelengths of 335/445 nm, and robustness against minor variations in reagent volume (±0.1 ml) or reaction time (±5 min) . Cross-validation with HPLC or spectrophotometric methods ensures accuracy in dosage forms and spiked plasma (mean recovery: 97.77% ±1.19) .

Q. How does this compound exert its schistosomicidal activity at the molecular level?

this compound is enzymatically activated by sulfotransferases in Schistosoma mansoni to form a reactive ester intermediate, which alkylates parasitic DNA, disrupting replication . Resistance arises from loss-of-function mutations in the sulfotransferase gene (SmSULT), as shown via linkage mapping (LOD = 31 on chromosome 6) and RNAi knockdowns . Crystallographic studies confirm drug-enzyme binding interactions, guiding rational derivative design for broader species efficacy .

Q. What are the primary considerations for designing in vitro assays to evaluate this compound efficacy?

Use juvenile (1–5-day-old) and adult (25-day-old) schistosomula to assess stage-specific susceptibility. Statistical analysis via non-parametric tests (e.g., Kruskal-Wallis) is critical, as strain- and sex-dependent responses exist. For example, R1 strain females show absolute resistance post-day 25, while males exhibit partial susceptibility (17.7% reduction vs. 69.2% in LE strain) . Include controls for baseline parasite viability and validate results across multiple biological replicates.

Advanced Research Questions

Q. How can contradictory data on this compound’s efficacy across Schistosoma strains be resolved methodologically?

Contradictions arise from genetic heterogeneity (e.g., SmSULT mutations) and hybridization events (e.g., S. bovis x S. haematobium hybrids). Combine whole-genome sequencing with functional assays (e.g., CRISPR-Cas9 knockouts) to map resistance loci . For hybrids, perform SNP analysis and in vitro drug exposure trials to quantify hybrid-specific susceptibility . Standardize protocols for parasite age, culture conditions, and drug exposure times to minimize variability .

Q. What experimental strategies are recommended to mitigate false positives/negatives in this compound resistance studies?

• False positives: Use isogenic parasite lines to control for genetic background effects. Confirm resistance via enzymatic assays (e.g., sulfotransferase activity with PAPS cofactor) .
• False negatives: Optimize drug concentration ranges using dose-response curves (e.g., IC₅₀ values) and include sensitive strains as internal controls. Apply orthogonal methods like LC-MS to verify metabolite activation .

Q. How can spectrofluorimetric methods be adapted for high-throughput screening of this compound derivatives?

Automate derivatization steps using microplate readers and robotic liquid handlers. Validate derivative-specific fluorescence profiles (e.g., excitation/emission shifts) and cross-reference with LC-MS for structural confirmation. Use spiked plasma pools to assess matrix effects and recovery rates .

Q. What are the implications of this compound’s species-specific activation for cross-species schistosomiasis control?

S. haematobium lacks functional sulfotransferase orthologs, rendering this compound ineffective. Structure-activity relationship (SAR) studies guided by SmSULT crystallography can identify derivatives with broader specificity. For example, modifying the quinoline scaffold or esterification site may enhance binding to divergent sulfotransferases .

Q. Methodological Resources

• Analytical Validation: Follow ICH Q2B guidelines for specificity, linearity, accuracy, and precision .
• Genetic Mapping: Utilize CRISPR-Cas9 and RNAi for functional genomics in schistosomes .
• Data Reporting: Adhere to standards for qualitative research (e.g., SRQR) and include raw data in supplemental files .