Enclomiphene

Synthetic Routes and Reaction Conditions: The synthesis of enclomiphene involves the preparation of clomiphene, which is a mixture of cis-clomiphene (zuclomiphene) and trans-clomiphene (this compound). One method for synthesizing clomiphene uses a single solvent, such as dichloromethane, in a one-pot reaction . The process involves the reaction of 2-chloro-1,2-diphenylethene with 4-(2-chloro-1,2-diphenylethenyl)phenol in the presence of a base, followed by purification to isolate the trans isomer, this compound .

Industrial Production Methods: Industrial production of this compound typically follows similar synthetic routes but on a larger scale. The process involves optimizing reaction conditions to maximize yield and purity, followed by large-scale purification techniques to isolate this compound from the mixture of isomers .

Primary Reaction Types

Enclomiphene undergoes three principal reaction types under controlled laboratory conditions :

• Oxidation : The compound’s phenolic rings are susceptible to oxidation, forming quinones under strong oxidizing agents like potassium permanganate.

• Reduction : The double bond in the chlorinated diphenylethylene moiety is reduced to an alcohol using hydride donors .

• Substitution : The chlorine atom undergoes nucleophilic displacement, particularly in polar aprotic solvents, yielding derivatives like methoxy-enclomiphene .

Synthetic Routes

This compound citrate is synthesized via a multi-step process :

• Horner-Wadsworth-Emmons Reaction :

  • 4-Hydroxybenzophenone reacts with N-(2-chloroethyl)-diethylamine to form a phenyl ether intermediate.

  • Condensation with dimethyl chloro(phenyl methylphosphonate) in tetrahydrofuran (THF) yields this compound base with >95% stereoselectivity .

• Citrate Salt Formation :

  • The base is treated with citric acid in acetone, producing this compound citrate with <0.4% cis-isomer impurities .

Key Industrial Conditions :

• Solvent: Dichloromethane (8 volumes) at 25°C .

• Chlorinating Agent: Dichlorodimethylhydantoin (0.51 mol equivalents) under anhydrous conditions to minimize impurities .

Metabolic Pathways

In vivo, this compound is metabolized primarily by hepatic enzymes :

• Phase I Metabolism : CYP2D6 and CYP3A4 mediate oxidative demethylation and hydroxylation.

• Phase II Metabolism : Glucuronidation enhances water solubility for renal excretion.

Metabolite Stability :

• Serum half-life: ~24 hours due to tissue accumulation .

• Sustained LH elevation persists for ≥7 days post-discontinuation .

Stability and Decomposition

Thermal Stability :

• Melting point: 147°C (onset) with decomposition at >200°C, releasing toxic fumes .

• Critical Storage Conditions :

  • Temperature: 2–8°C in airtight containers .

  • Incompatibilities: Strong acids/alkalis, oxidizing agents .

Photodegradation :

• Exposure to UV light induces cis-isomer formation, necessitating amber packaging .

Comparative Reaction Kinetics

Data from enantiomerically pure synthesis :

Functional Group Reactivity

• Citrate Counterion : Enhances aqueous solubility (1.2 mg/mL at pH 7.4) but does not participate in redox reactions .

• Chlorine Atom : Serves as the primary site for nucleophilic substitution due to its electrophilic carbon .

Enclomiphene has a wide range of scientific research applications:

Chemistry: Used as a model compound for studying selective estrogen receptor modulators.

Biology: Investigated for its effects on the hypothalamic-pituitary-gonadal axis.

Medicine: Primarily used in the treatment of male hypogonadism to increase testosterone levels.

Industry: Utilized in the development of new therapeutic agents targeting estrogen receptors.

Enclomiphene acts by antagonizing estrogen receptors in the pituitary gland. This disruption of the negative feedback loop by estrogen leads to an increase in gonadotropin secretion, which in turn stimulates the gonads to produce more testosterone . The molecular targets include estrogen receptors in the hypothalamus and pituitary gland, and the pathways involved are the hypothalamic-pituitary-gonadal axis .

Enclomiphene vs. Zuclomiphene

Zuclomiphene, the cis-isomer of clomiphene, constitutes ~40% of clomiphene citrate formulations. Key differences include:

• Antiviral Efficacy : Both isomers inhibit Ebola virus (EBOV) entry with similar potency (IC50: ~1.0–1.4 µM) .
• Metabolism : this compound is metabolized to 4-hydroxy-enclomiphene, while zuclomiphene forms 4-hydroxy-zuclomiphene, both retaining antiviral activity .

This compound vs. Clomiphene Citrate

Clomiphene citrate is a racemic mixture (~60:40 this compound:zuclomiphene) used off-label for male hypogonadism. Critical distinctions include:

• Mechanistic Overlap : Both inhibit EBOV entry via cholesterol trafficking disruption, with clomiphene’s IC50 (~1.2 µM) nearly matching this compound’s (~1.0 µM) .
• Clinical Preference : this compound is favored for long-term male therapy due to its safety profile, whereas clomiphene’s zuclomiphene component raises estrogenic risks .

This compound vs. Tamoxifen

Tamoxifen, another SERM, is used in breast cancer and infertility.

Research Findings and Data Tables

Table 1: Hormonal Changes in Hypogonadal Men (Clomiphene vs. This compound)

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Table 2: Antiviral Potency Against EBOV Entry

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Enclomiphene, a selective estrogen receptor modulator (SERM), is primarily recognized for its role in treating male hypogonadism and infertility. Its biological activity is characterized by both estrogenic and anti-estrogenic properties, influencing various hormonal pathways and physiological responses.

This compound acts on estrogen receptors in a manner that can be both agonistic and antagonistic, depending on the tissue context. This duality allows it to stimulate the hypothalamic-pituitary-gonadal (HPG) axis, leading to increased production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn promotes testosterone synthesis in the testes.

• Agonist Activity : this compound exhibits agonistic effects on certain tissues, enhancing estrogen receptor activity, which can lead to increased body weight and food intake in animal models .
• Antagonist Activity : Conversely, at higher doses, it can block estrogen's effects, particularly in reproductive tissues, thus inhibiting processes like sexual receptivity and prolactin secretion .

Testosterone Restoration

Recent studies have highlighted this compound's effectiveness in restoring testosterone levels in men with secondary hypogonadism. A notable clinical trial involved administering varying doses of this compound citrate over a period of six weeks:

Results showed that this compound significantly increased serum testosterone levels without disproportionately raising dihydrotestosterone (DHT), contrasting with transdermal testosterone treatment which led to higher DHT levels .

Hormonal Effects

The hormonal profile following this compound treatment demonstrated significant increases in both LH and FSH levels, confirming its role in stimulating endogenous testosterone production:

• Total Testosterone : Increased from baseline to therapeutic range.
• LH/FSH Ratio : Elevated LH levels were observed post-treatment, indicating effective stimulation of the testes .

Pharmacokinetics

This compound is rapidly absorbed with an elimination half-life of approximately 10 hours. Steady-state concentrations are achieved at doses around 25 mg, reflecting its pharmacodynamic stability and efficacy .

Case Studies

• Study on Older Men : A study involving older men with low testosterone levels demonstrated that this compound citrate effectively normalized testosterone levels within two weeks without significant side effects or changes in DHT levels .
• Animal Models : Research on ovariectomized rats indicated that this compound could inhibit estrogen-induced changes in reproductive tissues while promoting weight gain through its agonistic effects on specific tissues .

Basic Research Questions

Q. What are the key considerations for designing a controlled study to evaluate enclomiphene’s efficacy in restoring testosterone levels in hypogonadal males?

• Methodological Guidance : Use a randomized, single-blind design with dose-ranging arms (e.g., 6.25–25 mg/day) and an active comparator (e.g., transdermal testosterone). Include baseline hormonal profiling (total testosterone, LH, FSH) and standardized assays (e.g., immunoassays for hormone quantification). Monitor covariates like BMI and age, as these may influence metabolic responses . Ensure exclusion criteria address confounding factors (e.g., diabetes, CYP2D6 polymorphisms) .

Q. How should researchers standardize hormone measurement protocols to ensure reproducibility across this compound studies?

• Methodological Guidance : Employ centralized laboratories for consistency in assays (e.g., ADVIA® systems for lipid panels, ELISA for osteocalcin). Report detailed methodologies for blood collection timing (e.g., morning sampling to account for diurnal testosterone variations) and validation parameters (e.g., intra-assay coefficients of variation) . Cross-reference with ICH guidelines for bioanalytical method validation.

Q. What are the recommended dosages for this compound in preclinical vs. clinical research, and how are these determined?

• Methodological Guidance : Preclinical studies often use rodent models with doses adjusted for metabolic scaling (e.g., 1–5 mg/kg). For clinical trials, start with 12.5–25 mg/day based on phase II data showing dose-dependent increases in testosterone without severe adverse effects. Justify deviations using pharmacokinetic modeling (e.g., AUC comparisons between isomers) .

Advanced Research Questions

Q. How can researchers resolve contradictions in this compound’s metabolic clearance rates observed in outlier subjects (e.g., prolonged serum detection)?

• Methodological Guidance : Conduct pharmacogenetic analyses (e.g., CYP2D6 isoform profiling) to identify metabolic outliers. Use longitudinal sampling to track this compound and zuclomiphene levels over time. Apply mixed-effects models to account for interindividual variability in pharmacokinetic parameters . Include raw data in supplementary materials for transparency .

Q. What experimental strategies differentiate this compound’s anti-estrogenic effects from zuclomiphene’s estrogenic activity in dual-isomer formulations?

• Methodological Guidance : Use chiral chromatography to isolate isomers and perform receptor-binding assays (e.g., competitive ERα/β binding). Compare transcriptional activity in estrogen-responsive cell lines (e.g., MCF-7) using luciferase reporters. Reference isomer-specific pharmacokinetic data to contextualize in vivo effects .

Q. How should long-term studies address this compound’s potential estrogen rebound effects after discontinuation?

• Methodological Guidance : Design washout phases with frequent hormonal monitoring (e.g., weekly estradiol/total testosterone measurements). Use crossover designs to compare rebound kinetics against baseline. Incorporate patient-reported outcomes (e.g., mood scales) to assess clinical relevance of biochemical fluctuations .

Q. What statistical approaches are optimal for analyzing this compound’s dose-response relationships in heterogeneous populations?

• Methodological Guidance : Apply dose-response meta-analysis to pooled data from multiple trials. Use Bayesian hierarchical models to adjust for covariates (e.g., BMI, age). Report effect sizes with 95% credible intervals and sensitivity analyses for outlier exclusion .

Q. Data Management & Reporting

Q. How should this compound researchers structure supplemental data to enhance reproducibility?

• Methodological Guidance : Follow FAIR principles:

• Raw Data : Include hormone assay raw outputs (e.g., plate reader values) and pharmacokinetic time-series.
• Metadata : Document assay conditions (e.g., lot numbers, calibration curves).
• Code : Share scripts for statistical analysis (e.g., R/Python) .

Q. What ethical considerations are critical when designing this compound trials involving human subjects?

• Methodological Guidance : Address informed consent for genetic testing (e.g., CYP2D6). Implement DSMB oversight for adverse events (e.g., vision disturbances). Adhere to Declaration of Helsinki principles for vulnerable populations (e.g., fertility patients) .

Q. Contradictions & Gaps

Q. How do conflicting findings on this compound’s impact on gonadotropins (LH/FSH) inform future research directions?

• Methodological Guidance : Reconcile discrepancies by comparing study designs (e.g., dosing duration, population BMI). Conduct mechanistic studies using hypothalamic-pituitary explants to isolate this compound’s central vs. peripheral effects .