Norethisterone Acetate – Impurity C (CAS 1175129-26-6)

Norethisterone Acetate – Impurity C (CAS 1175129-26-6)

In pharmaceutical chemistry and quality control, impurities in drug substances must be identified, characterized, and controlled. One such impurity is Norethisterone Acetate – Impurity C, a related compound structurally derived from the active steroid norethisterone acetate. The Pharmaffiliates listing provides details about its identity, nomenclature, properties, and handling. 

This article discusses what this impurity is, why it matters, its chemical features, and the significance in pharmaceutical manufacturing.

What is Norethisterone Acetate – Impurity C?

  • CAS Number: 1175129-26-6 

  • Chemical Name: 3-Oxo-19-nor-17α-pregn-5-en-20-yn-17-yl Acetate

  • Molecular Formula: C₂₂H₂₈O₃ Molecular Weight: ≈ 340.46 g/mol 

  • Synonyms: (17α)-17-(Acetyloxy)-19-norpregn-5-en-20-yn-3-one; Δ-5(6)-Norethindrone Acetate; (8R,9S,10R,13S,14S,17R)-17-Ethynyl-13-methyl-3-oxo-… etc. 

  • Storage Conditions: 2–8 °C (refrigerator) 

  • Shipping Conditions: Ambient 

The listing is under the categories: impurities, pharmaceutical standards, intermediates, fine chemicals, steroids. 

It is offered as a reference standard (analytical standard), with availability of COA (Certificate of Analysis) and MSDS (Material Safety Data Sheet). 

Pharmaffiliates also lists related compounds (other impurities A, E, F, and the parent norethisterone acetate) for analytical comparison. 



Chemical and Structural Features

Because this is an impurity of norethisterone acetate, it shares much of the steroid backbone but differs by subtle structural changes:

  • It includes the acetate ester moiety (i.e. the “-yl Acetate”) at the 17α position, like many steroid esters.

  • The “3-oxo” indicates a ketone group at the 3-position, consistent with typical steroid carbonyl functionality.

  • The “19-nor” denotes that the compound is lacking the carbon at position 19 (i.e. “nor” indicates removal of carbon 19 relative to parent structure).

  • The “20-yn” suggests the presence of an alkyne (triple bond) at the 20-position.

  • There is a Δ5–6 double bond (i.e. “pregn-5-en”) in the steroid ring system.

  • Stereochemistry is indicated (8R,9S,10R,13S,14S,17R) in one of the synonyms.

These small modifications can arise during synthesis, degradation, side-reactions, or during storage. In pharmaceutical compounds, such impurities are carefully monitored because they may affect safety, activity, or regulatory acceptance.

Significance in Pharmaceuticals / Quality Control

Why identify and control Impurity C?

  1. Regulatory Compliance
    Regulatory authorities (e.g. ICH, FDA, EMA) require impurity profiling of drug substances. Each impurity above certain threshold levels must be identified, structurated, and controlled. Using well-characterized reference standards helps in quantification via chromatographic or spectrometric methods.

  2. Safety and Toxicology
    Although an impurity may be present in small amounts, if it has any adverse biological activity or toxicity, it can compromise the safety of the drug product. Understanding its structure is essential to assess potential risks.

  3. Analytical Method Development
    Reference standards for impurity C help in method validation (accuracy, specificity, sensitivity) for assays (e.g. HPLC, LC-MS). Distinguishing the impurity from the main drug peak is critical for reliable quantification.

  4. Stability Studies
    Over time, the parent compound (norethisterone acetate) or intermediates may degrade and form impurity C. Monitoring its formation under stress conditions (temperature, humidity, pH, light) helps define product shelf life and proper storage.

  5. Process Optimization
    In synthetic routes, certain side reactions or by-products might lead to formation of impurity C. Recognizing this helps chemists optimize reaction conditions, purification steps, and choose reagents to minimize its formation.

Handling, Storage, and Use as a Reference Standard

  • According to the Pharmaffiliates listing, it should be stored at 2–8 °C.

  • Shipping under ambient conditions suggests it is stable under those conditions during transit (short term). 

  • Because it is sold as a pharmaceutical reference standard, users will typically request COA (Certificate of Analysis) and MSDS to ensure identity, purity, safety, and handling protocols. 

  • Quantities available may range from milligrams up to grams or kilograms (depending on need) — the site mentions mg / gms / kg as units for ordering. 

Users (analytical labs, pharmaceutical companies) can inquire or request a bulk quote via the listing page. 

Broader Context: Norethisterone Acetate and Impurities

Norethisterone acetate is a well-known synthetic progestin (a progestogen steroid) used in various hormonal therapies (contraceptives, hormone replacement). In the production and quality assessment of norethisterone acetate, multiple impurities can arise (labelled typically A, B, C, etc.). The Pharmaffiliates page also lists Impurity A, E, F along with the parent compound. 

Each impurity will have its own chemical structure, properties, and risk profile. Together, the impurity profile helps in defining the purity specification and acceptance criteria for the drug substance.

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