S-4 (Andarine) Overview
S-4, also known as Andarine and by the developmental designation GTx-007, is a synthetic nonsteroidal selective androgen receptor modulator (SARM) of the arylpropionamide chemical class. It was originally developed by GTx, Inc. (the same developer as MK-2866 / Ostarine and S-23) and is one of the earlier SARM compounds advanced through preclinical and early clinical research, with documented investigations across muscle wasting, osteoporosis, and benign prostatic hypertrophy (BPH) indications.
S-4 has been characterized in the primary literature as a high-affinity androgen receptor ligand with reported binding K_i of approximately 4 nM. It is widely cited as a reference SARM in androgen receptor pharmacology research, structure-activity relationship studies of the arylpropionamide class, and anti-doping analytical chemistry. S-4’s clinical development is also notable for a documented dose-limiting visual disturbance (yellow-tinged vision) observed in clinical research, which is part of the published research record on the compound.
S-4 is not approved for human or veterinary use and is supplied strictly for laboratory and analytical research purposes.
Mechanism of Action
S-4 binds the androgen receptor ligand-binding domain with high affinity and acts as a partial agonist of the AR. Published in vitro and preclinical characterizations describe differential transcriptional output across androgen-responsive cell types, with full-agonist transcriptional activity in cell models representative of muscle and bone tissue and reduced (partial agonist) activity in prostate-derived reporter models. In published BPH animal models, S-4 has been reported to reduce prostate weight with efficacy comparable to finasteride.
Reported characterizations include:
- AR binding K_i ≈ 4 nM
- Oral bioavailability in published rodent pharmacokinetic studies
- Partial agonist activity at the androgen receptor
- Non-aromatizable arylpropionamide scaffold
- Documented dose-limiting visual side effect (transient yellow-tinged vision) observed in clinical research, attributed to interaction with retinal photoreceptor signaling
Chemical Structure & Identification
- Chemical Name: (2S)-3-(4-Acetamidophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide
- Synonyms: S-4; S4; Andarine; GTx-007; GTx007
- Chemical Class: Nonsteroidal arylpropionamide SARM
- CAS Number: 401900-40-1
- Molecular Formula: C₁₉H₁₈F₃N₃O₆
- Molecular Weight (average): 441.36 g/mol
- Exact Mass (monoisotopic): 441.115 g/mol
- UNII: 7UT2HAH49H
Structural Description: S-4 is a small-molecule, nonsteroidal androgen receptor ligand of the arylpropionamide chemical class — structurally related to MK-2866 (Ostarine) and S-23. The molecule consists of a 4-acetamidophenoxy ether, a chiral (S)-configured 2-hydroxy-2-methylpropanamide central group, and an aniline-derived arm bearing both a 4-nitro substituent and a 3-trifluoromethyl group. The 4-acetamido substitution on the phenoxy ring and the 4-nitro substitution on the aniline ring (in contrast to the 4-cyano substitutions in MK-2866) are key structural features distinguishing S-4 from other arylpropionamide-class SARMs. Structural identification and molecular data are referenced against PubChem.
Physical and Chemical Properties
- Appearance: White to off-white solid powder
- Solubility: Soluble in DMSO 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
S-4 is commonly referenced in laboratory research involving:
- Androgen receptor binding, competition, and transactivation assays
- SARM structure-activity relationship (SAR) analysis within the arylpropionamide chemical class
- Comparative AR ligand pharmacology alongside MK-2866 (Ostarine) and S-23
- Partial agonist receptor pharmacology and ligand-binding domain conformational studies
- Analytical and reference-standard work, including LC-MS/MS method development referenced in anti-doping analytical literature (Hansson et al., Thevis, and others)
- Urinary metabolite identification and forensic toxicology research
- Visual system research models (S-4 is one of the few SARMs with a documented retinal interaction signal, making it a reference compound for research into off-target AR ligand effects on visual physiology)
Research Background & Regulatory Context
S-4 has been included on the World Anti-Doping Agency (WADA) Prohibited List under the anabolic agents category since 2008, and is one of the most extensively characterized SARMs in anti-doping analytical literature. Clinical development of S-4 was constrained in part by the documented dose-limiting yellow-tinged vision side effect, which is part of the published research record on the compound. The U.S. Food and Drug Administration has issued multiple public consumer advisories naming SARMs broadly, including arylpropionamide-class compounds, in the context of unapproved bodybuilding and dietary supplement products. This published regulatory, clinical, and analytical record reinforces that S-4 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
S-4 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
S-4 (Andarine, GTx-007) is a structurally defined nonsteroidal arylpropionamide SARM developed by GTx, Inc. and characterized extensively in preclinical and early clinical research across multiple indications. Its high AR binding affinity, partial-agonist receptor profile, distinctive acetamido-phenoxy / nitro-trifluoromethyl substitution pattern, and well-documented analytical and clinical research record make it a widely used reference compound in controlled laboratory studies of androgen receptor signaling and anti-doping analytical method development.
| CAS Number | 401900-40-1 |
| Other Names | S4, S-4, S 4, Andarine, GTX-007, S-4 cpd, UNII-7UT2HAH49H, 7UT2HAH49H, GTX007, GTx 007, CHEMBL125236 |
| IUPAC Name | (2S)-3-(4-acetamidophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide |
| Molecular Formula | C₁₉H₁₈F₃N₃O₆ |
| Molecular Weight | 441.4 |
| Dry-Fill Capsule Concentration | 25mg |
| Liquid Concentration And Solution | 50mg/ml (PEG400) |
| Aliquot Concentration And Solution | 50mg/ml (PEG400, Propylene Glycol, Benzyl Benzoate, Benzyl Alcohol) |
