MK-2866 (Ostarine) Overview
MK-2866, also known as Ostarine and enobosarm, and by the developmental designations GTx-024, S-22, and VERU-024, is a synthetic nonsteroidal selective androgen receptor modulator (SARM) originally developed by GTx Inc. and subsequently advanced by Veru Pharmaceuticals. It is among the most extensively studied SARMs in the published literature, characterized as a high-affinity androgen receptor ligand with reported binding K_i of approximately 3.8 nM.
Enobosarm has been advanced through Phase III clinical research investigations across multiple indications and is currently in active Phase III development for androgen-receptor-positive breast cancer and for body-composition preservation in patients receiving GLP-1 receptor agonists. As a result, MK-2866 has one of the most extensive clinical, pharmacokinetic, and analytical chemistry reference profiles of any SARM in the literature, making it a widely used reference compound in androgen receptor pharmacology and anti-doping analytical research.
MK-2866 is not approved for human or veterinary use and is supplied strictly for laboratory and analytical research purposes.
Mechanism of Action
MK-2866 binds the androgen receptor ligand-binding domain with high affinity and acts as a tissue-differential AR ligand. Published in vitro and preclinical characterizations describe differential transcriptional output across androgen-responsive cell types, with full-agonist transcriptional activity in muscle- and bone-derived cell models and reduced (partial agonist) activity in prostate-derived reporter models.
Reported characterizations include:
- AR binding K_i ≈ 3.8 nM
- Documented oral bioavailability and pharmacokinetic profile in published rodent, primate, and human studies (terminal half-life of approximately 6 hours in rodent IV pharmacokinetic studies)
- Non-aromatizable nonsteroidal arylpropionamide scaffold
- Extensively characterized in vitro metabolite profile relevant to analytical and forensic research
Chemical Structure & Identification
- Chemical Name: (2S)-3-(4-Cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide
- Synonyms: MK2866; MK 2866; Ostarine; Enobosarm; GTx-024; GTX024; S-22; VERU-024
- CAS Number: 841205-47-8
- Molecular Formula: C₁₉H₁₄F₃N₃O₃
- Molecular Weight: 389.33 g/mol
- PubChem CID: 11326715
- InChIKey: Available via PubChem
Structural Description: MK-2866 is a small-molecule, nonsteroidal androgen receptor ligand of the arylpropionamide chemical class. The molecule consists of a 4-cyanophenoxy ether, a chiral (S)-configured 2-hydroxy-2-methylpropanamide central group, and an aniline-derived arm bearing both a 4-cyano substituent and a 3-trifluoromethyl group. The two nitrile (cyano) functionalities, the trifluoromethyl group, and the secondary amide linkage are key structural features contributing to AR binding affinity, metabolic stability, and the compound’s distinctive mass spectrometric fingerprint. Structural identification and molecular data are referenced against PubChem.
Physical and Chemical Properties
- Appearance: White to off-white crystalline powder
- Solubility: Soluble in DMSO, ethanol, and similar organic solvents; poorly soluble in water
- Stability: Stable under dry, cool, light-protected storage conditions
- Recommended storage: -20 °C for long-term stability
Research Focus Areas
MK-2866 is commonly referenced in laboratory research involving:
- Androgen receptor binding, competition, and transactivation assays
- SARM structure-activity relationship (SAR) analysis, particularly within the arylpropionamide chemical class
- Nuclear receptor selectivity profiling
- AR ligand-binding domain conformation and coregulator recruitment studies
- Analytical and reference-standard work, including extensive LC-MS/MS method development referenced in anti-doping analytical literature
- In vitro metabolism, ADME, and forensic toxicology research (MK-2866 metabolite identification is one of the most thoroughly characterized in the SARM class)
- Comparative SARM evaluation alongside other arylpropionamide-class compounds and the broader nonsteroidal AR ligand family
Research Background & Regulatory Context
MK-2866 is included on the World Anti-Doping Agency (WADA) Prohibited List under the anabolic agents category and is among the most frequently detected SARM analytes in anti-doping testing programs. The U.S. Food and Drug Administration has issued multiple public consumer advisories naming Ostarine in the context of unapproved bodybuilding and dietary supplement products. This published regulatory and analytical record is part of the scientific literature on the compound and reinforces that MK-2866 is supplied strictly as a research reagent for laboratory and analytical use, not for any therapeutic, performance, dietary supplement, or other consumer application.
Research Use Disclaimer
MK-2866 is intended strictly for laboratory research use only (RUO). Not for human consumption, clinical use, veterinary use, therapeutic application, dietary supplement use, or diagnostic purposes. All handling and use must comply with applicable federal, state, and local laws and institutional laboratory safety standards.
Summary
MK-2866 (Ostarine, Enobosarm) is a structurally defined, exhaustively characterized nonsteroidal selective androgen receptor modulator with one of the deepest primary-literature and clinical-research records in the SARM class. Its arylpropionamide scaffold, well-defined binding and metabolite profiles, and active Phase III clinical development make it a widely used reference compound in controlled laboratory studies of androgen receptor signaling and in anti-doping analytical method development.
| CAS Number | 1202044-20-9 |
| Other Names | MK2866, MK 2866, Ostarine, Enobosarm, Enobosarm-d4 |
| IUPAC Name | (2S)-3-(4-cyano-2,3,5,6-tetradeuteriophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide |
| Molecular Formula | C₁₉H₁₄F₃N₃O₃ |
| Molecular Weight | 389.3 |
| Dry-Fill Capsule Concentration | 15mg |
| Liquid Concentration And Solution | 30mg/ml (PEG400) |
| Aliquot Concentration And Solution | 50mg/ml (PEG400, Propylene Glycol, Benzyl Benzoate, Benzyl Alcohol) |
