Enobosarm: Molecular Structure
Chemical properties, amino acid sequence, and structural analysis
📌TL;DR
- •Molecular formula: C19H14F3N3O3
- •Molecular weight: 389.33 Da
- •Half-life: Approximately 24 hours (supporting once-daily oral dosing)
Amino Acid Sequence
48 amino acids
Formula
C19H14F3N3O3
Molecular Weight
389.33 Da
Half-Life
Approximately 24 hours (supporting once-daily oral dosing)
Molecular Structure#
Enobosarm (Ostarine, GTx-024, MK-2866) is a nonsteroidal selective androgen receptor modulator belonging to the aryl propionamide class of SARMs. Unlike the peptide therapies that comprise most of this site's content, enobosarm is a synthetic small molecule that is orally bioavailable and does not require injection.
The molecule was designed to bind the androgen receptor (AR) ligand-binding domain with high affinity while inducing a conformational change in the receptor that differs from that induced by testosterone. This conformational difference leads to differential recruitment of coregulator proteins in different tissues, which is the molecular basis for tissue selectivity.
Chemical Name#
(2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2-hydroxy-2-methylpropanamide
Key Structural Features#
- Trifluoromethyl group: Enhances metabolic stability and AR binding affinity
- Two cyano (nitrile) groups: On both the aniline and phenoxy rings, contributing to AR binding
- Chiral center: The (S)-configuration at the propionamide center is critical for biological activity
- Hydroxyl group: Participates in hydrogen bonding within the AR ligand-binding pocket
- No steroid backbone: Fundamentally different from testosterone, enabling tissue selectivity
Chemical Properties#
| Property | Value |
|---|---|
| Molecular formula | C19H14F3N3O3 |
| Molecular weight | 389.33 Da |
| CAS number | 841205-47-8 |
| Type | Nonsteroidal aryl propionamide SARM |
| SMILES | O=C(NC1=CC=C(C#N)C(C(F)(F)F)=C1)C@@(O)COC2=CC=C(C#N)C=C2 |
| Chirality | (S)-enantiomer active |
| Solubility | Organic solvents (DMSO, ethanol) |
| Oral bioavailability | Yes (supports once-daily oral dosing) |
Pharmacokinetics#
Enobosarm has favorable pharmacokinetic properties for an oral medication:
- Oral bioavailability: Sufficient for therapeutic exposure via oral route
- Half-life: Approximately 24 hours, supporting once-daily dosing
- Metabolism: Hepatic metabolism (CYP-mediated); ALT elevations observed in some patients suggest hepatic burden
- Protein binding: Not fully characterized publicly
- Steady state: Achieved within approximately 5 days of daily dosing based on the ~24-hour half-life
Pharmacodynamics#
- AR binding affinity: High affinity for the androgen receptor ligand-binding domain
- Tissue selectivity ratio: Anabolic activity in muscle/bone with reduced androgenic activity in prostate/sebaceous glands
- Onset: Lean mass changes detectable within 12 weeks in clinical trials
- Dose response: Dose-dependent increases in lean body mass at 1 mg and 3 mg
Comparison with Related Molecules#
| Feature | Enobosarm | Testosterone | LGD-4033 |
|---|---|---|---|
| Class | Nonsteroidal SARM | Steroidal androgen | Nonsteroidal SARM |
| Molecular weight | 389 Da | 288 Da | 338 Da |
| Route | Oral | IM/topical | Oral |
| Tissue selectivity | High | None (full agonist) | Moderate |
| Half-life | ~24 hours | Variable by formulation | ~26 hours |
| Prostate stimulation | Minimal | Significant | Minimal |
| AR mechanism | Partial agonist (tissue-selective) | Full agonist | Partial agonist |
| Regulatory status | Investigational | Approved | Investigational |
Mechanism of Tissue Selectivity#
The tissue selectivity of enobosarm is mediated by differential coregulator recruitment:
- In muscle: The AR-enobosarm complex recruits coactivators (SRC-1, p300) that drive anabolic gene expression, promoting muscle protein synthesis
- In prostate: The AR-enobosarm complex has reduced ability to recruit the same coactivators, resulting in minimal prostatic stimulation
- In bone: Intermediate coactivator recruitment promotes osteoblast activity and bone preservation
This mechanism differs from 5-alpha reductase inhibitor approaches, which reduce DHT in prostate but do not achieve the same degree of tissue selectivity for muscle.
Stability#
As a small molecule:
- Chemically stable at room temperature
- Does not require refrigeration or cold chain storage
- No reconstitution needed
- Significantly simpler handling than peptide therapeutics
Related Reading#
Frequently Asked Questions About Enobosarm
What type of molecule is enobosarm?
Enobosarm is a nonsteroidal small molecule, not a peptide. It belongs to the aryl propionamide class of selective androgen receptor modulators (SARMs). Its molecular formula is C19H14F3N3O3 with a molecular weight of 389.33 Da. It is administered orally and does not require injection.
What is the half-life of enobosarm?
Enobosarm has an approximate half-life of 24 hours, supporting once-daily oral dosing. This extended half-life for a small molecule contributes to consistent drug exposure and convenient dosing regimen.
How does enobosarm differ structurally from testosterone?
Enobosarm is a nonsteroidal compound that does not share the four-ring steroid backbone of testosterone. Instead, it achieves androgen receptor binding through an aryl propionamide scaffold with a trifluoromethyl group and two cyano groups. This structural difference is what enables its tissue-selective activity through differential coregulator recruitment.
Is enobosarm a peptide?
No. Enobosarm is a small molecule drug (MW 389.33 Da), not a peptide. It is orally bioavailable and does not require injection, reconstitution, or refrigerated storage. It is classified as a SARM on this site because of its relevance to the musculoskeletal peptide landscape and its role in preserving muscle during peptide-based (GLP-1 agonist) weight loss therapy.
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