What Is YK-11? A Steroidal Androgen Receptor Partial Agonist Explained

What Is YK-11?

Short answer: YK-11 is a synthetic steroid, (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (CAS 1370003-76-1), that acts as a partial agonist of the androgen receptor in cell-based assays. It has the formula C₂₅H₃₄O₆ and a molecular weight of 430.5 g/mol. It is often called a SARM, but unlike most SARMs it is built on a steroid skeleton. To buy YK-11 as a documented reference compound, see the product page.

That is the summary. The more interesting story is how YK-11 activates the receptor differently from a natural androgen, and what that looks like in published cell-culture work.

What is YK-11, chemically speaking?

Start with a 19-norsteroid core: four fused rings, with a ketone at position 3 and a double bond in the first ring, the same basic layout found in many synthetic steroids. What makes YK-11 unusual is the D-ring. At carbon 17 it carries a five-membered cyclic orthoester, a ring containing two oxygens, capped with a methoxy and a methyl group. Attached to that ring is an exocyclic double bond leading to a methyl ester (PubChem CID 119058028).

PubChem lists the compound as YK-11 (CID 119058028) with the FDA UNII Z9748J6B0R, the InChIKey KCQHQCDHFVGNMK-PQUNLUOYSA-N and six defined stereocenters. Note that PubChem links the CAS number 1370003-76-1 to several records, so the CID and InChIKey are the cleaner identity checks.

Is YK-11 a steroid or a SARM?

Both labels get used, and both have a point. Structurally, YK-11 is a steroid. Functionally, the Kanno group described it as a selective androgen receptor modulator because it activated the receptor only partially and in a gene-selective way (Kanno et al., Biol Pharm Bull 2011). Most SARMs, such as ostarine (MK-2866), are nonsteroidal, so the plain description is “a steroidal SARM” or “a steroidal androgen receptor partial agonist.” It is not a peptide.

How does YK-11 work? Partial agonism, step by step

The first characterization, published in 2011, used reporter-gene and interaction assays in cultured cells (Kanno et al., Biol Pharm Bull 2011):

1. Binding and translocation. YK-11 binds the androgen receptor and speeds up the receptor’s move into the nucleus.
2. No N/C interaction. When natural androgens bind, the receptor’s amino-terminal and carboxyl-terminal ends fold together (the “N/C interaction”). YK-11 did not induce that interaction, and it blocked the interaction normally induced by 5α-dihydrotestosterone (DHT).
3. Partial activation. In an androgen response element luciferase assay, YK-11 behaved as a partial agonist, which the authors linked to the missing N/C interaction.
4. Gene selectivity. In MDA-MB 453 cells, YK-11’s effect relative to an androgen agonist varied by gene.

A 2022 follow-up in the same cell line found different patterns of receptor recruitment to target-gene enhancers for YK-11 versus DHT, and docking suggested YK-11’s bulky C17 group shifts helices 11 and 12 of the receptor (Kanno et al., Exp Cell Res 2022).

What do the cell-model studies show?

The table summarizes the in vitro findings reported by the Kanno laboratory and identity data from PubChem.

What this tells us: the best-known YK-11 finding is the follistatin link. In C2C12 myoblasts, YK-11, but not DHT, induced follistatin, and blocking follistatin with an antibody reversed YK-11’s effect on myogenic differentiation (Kanno et al., Biol Pharm Bull 2013). That is where the frequent “myostatin inhibitor” description comes from. It is an interpretation of a cell-culture result, since follistatin is a known myostatin-binding protein; the paper itself measured follistatin, not direct myostatin inhibition. The osteoblast work found the YK-11 effects were reduced by an androgen receptor antagonist (Yatsu et al., Biol Pharm Bull 2018).

Why the orthoester matters for handling and analysis

Analytical chemists studying YK-11 describe its orthoester-derived D-ring group as arguably labile, meaning it is expected to break down relatively easily (Piper et al., Drug Test Anal 2018). In practical terms, that is a reason to rely on a current, lot-specific COA and to treat solution stability as something to confirm rather than assume.

How is YK-11 tested?

All applicable tests are performed on our products, and the certificates are posted publicly. Open the current YK-11 certificate of analysis to review lot results.

What formats is YK-11 supplied in for research?

Modern Aminos lists YK-11 in dry-fill capsule, liquid and oil research formats. The liquid and oil formats are what searches for “injectable YK-11” usually refer to, but every format is a laboratory reference material, not a product for injection or any in vivo use. See the YK-11 product page for current formats and availability.

Where YK-11 sits among other androgen receptor research tools

YK-11 is the steroidal outlier in a mostly nonsteroidal class. Compare it with the aryl-propionamide ostarine and the oxadiazole ester RAD-150. For a receptor-independent metabolic tool, see what BAM15 is.

Frequently asked questions

What is YK-11?

YK-11 is a synthetic steroid (CAS 1370003-76-1, C25H34O6, 430.5 g/mol) that acts as a partial agonist of the androgen receptor in cell-based assays. It is supplied for laboratory research use only.

Is YK-11 a steroid or a SARM?

Structurally it is a steroid. It was described as a selective androgen receptor modulator because it activates the receptor partially and gene-selectively in cell assays.

Is YK-11 a myostatin inhibitor?

Not directly, based on the published data. In C2C12 myoblasts YK-11 induced follistatin, a myostatin-binding protein, and blocking follistatin reversed its effect on differentiation.

Is there an injectable YK-11?

Modern Aminos supplies YK-11 in liquid and oil research formats, but no format is intended for injection or any in vivo use. All formats are laboratory reference materials.

How is YK-11 purity verified?

All applicable tests are performed on our products, and the current YK-11 certificate of analysis is posted publicly on the Modern Aminos COA page.

Where can I find YK-11 for sale for research?

Modern Aminos lists YK-11 on its product page in capsule, liquid and oil research formats, for laboratory research use only.

References

1. Kanno Y, Hikosaka R, Zhang SY, et al. (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK11) is a partial agonist of the androgen receptor. Biol Pharm Bull. 2011;34(3):318-323. doi:10.1248/bpb.34.318 (PMID 21372378)
2. Kanno Y, Ota R, Someya K, Kusakabe T, Kato K, Inouye Y. Selective androgen receptor modulator, YK11, regulates myogenic differentiation of C2C12 myoblasts by follistatin expression. Biol Pharm Bull. 2013;36(9):1460-1465. doi:10.1248/bpb.b13-00231 (PMID 23995658)
3. Yatsu T, Kusakabe T, Kato K, Inouye Y, Nemoto K, Kanno Y. Selective androgen receptor modulator, YK11, up-regulates osteoblastic proliferation and differentiation in MC3T3-E1 cells. Biol Pharm Bull. 2018;41(3):394-398. doi:10.1248/bpb.b17-00748 (PMID 29491216)
4. Kanno Y, Saito N, Saito R, et al. Differential DNA-binding and cofactor recruitment are possible determinants of the synthetic steroid YK11-dependent gene expression by androgen receptor in breast cancer MDA-MB 453 cells. Exp Cell Res. 2022;419(2):113333. doi:10.1016/j.yexcr.2022.113333 (PMID 36030969)
5. Piper T, Dib J, Putz M, et al. Studies on the in vivo metabolism of the SARM YK11: identification and characterization of metabolites potentially useful for doping controls. Drug Test Anal. 2018;10(11-12):1646-1656. doi:10.1002/dta.2527 (PMID 30379415)
6. National Center for Biotechnology Information. PubChem Compound Summary for CID 119058028, YK-11. pubchem.ncbi.nlm.nih.gov/compound/119058028

YK-11 is a steroid that behaves like a partial, gene-selective androgen receptor agonist in cell models, with a follistatin finding that explains much of the interest in it. Check identity by CID and InChIKey, and rely on a current COA.