What Is MK-777?
Short answer: MK-777, also sold as acetamoren, is identified by CAS 950841-87-9. PubChem files that CAS number under N-acetyl ibutamorelin (CID 57595228), an N-acetylated derivative of the growth hormone secretagogue ibutamoren (MK-0677), with the formula C29H38N4O6S and a molecular weight of 570.7 g/mol. It is not a SARM and not a peptide. To buy MK-777 (acetamoren) as a documented reference compound, see the product page.
One honest caveat up front: “MK-777” and “acetamoren” do not appear as names in PubChem or in the PubMed literature. The identity in this guide rests on the CAS number, and the rest of the article is careful to separate what is published about the structure from what is not.
What is MK-777, chemically speaking?
Start with ibutamoren. It is a spiro compound: a piperidine ring and an indoline ring share a single carbon, and the indoline nitrogen carries a methylsulfonyl group. From the piperidine nitrogen, an amide links to a chiral serine-derived unit protected as a benzyl ether, and from there a second amide connects to 2-amino-2-methylpropanoic acid (aminoisobutyric acid). In MK-777 that terminal amino group is capped with an acetyl group (CH3CO–). That one change adds C2H2O to the formula, which is exactly the difference between the two PubChem records (PubChem CID 57595228; PubChem CID 178024).
PubChem gives the compound the FDA UNII DHZ77GVH76, the InChIKey YUZUIUJPTKQSNL-XMMPIXPASA-N and one defined stereocenter, at the serine-derived carbon.
MK-777 vs. ibutamoren: what is the difference?
| Property | MK-777 (N-acetyl ibutamorelin) | Ibutamoren (MK-0677) |
|---|---|---|
| PubChem CID | 57595228 | 178024 |
| Molecular formula | C29H38N4O6S | C27H36N4O5S |
| Molecular weight | 570.7 g/mol | 528.7 g/mol |
| Exact mass | 570.2512 Da | 528.2406 Da |
| XLogP3 | 1.6 | 1.3 |
| Topological polar surface area | 134 Å2 | 130 Å2 |
| H-bond donors / acceptors | 2 / 7 | 2 / 7 |
| Rotatable bonds | 9 | 8 |
What this tells us: the acetyl cap trades a free primary amine for an amide. The donor count stays at two because the new amide N–H replaces the amine’s donor role, while the molecule gets slightly heavier, slightly more lipophilic and one rotatable bond longer. Whether that change alters receptor activity is not something the published literature answers; any claim either way would be an interpretation, not a finding.
What is known about the parent compound, ibutamoren?
Ibutamoren was described in 1995 as L-163,191 (MK-0677), a nonpeptide growth hormone secretagogue. In rat pituitary cells in culture it released growth hormone with an EC50 of 1.3 nM, and it was mechanistically indistinguishable from the peptide GHRP-6 while distinguishable from growth hormone-releasing hormone (Patchett et al., PNAS 1995). That is the published biology for the parent. No equivalent primary paper for the N-acetyl derivative turned up in PubMed or Europe PMC searches.
Why does the parent matter here? Most of what gets written online about MK-777 borrows ibutamoren’s profile. That is a reasonable starting hypothesis for a research question, since the two share almost the whole scaffold, but it is a hypothesis. Small changes at a terminal amine can change how a molecule binds its receptor, and until the acetylated compound is characterized directly, its activity remains an open question rather than a known property.
Is MK-777 a SARM or a peptide?
Neither. Searches like “mk-777 sarm” and “mk 777 peptide” are common, but the structure does not support either label. It does not target the androgen receptor, which is what defines a SARM; compare a true SARM such as ostarine (MK-2866). And while it is assembled partly from amino-acid-derived units (a serine-derived core and aminoisobutyric acid), the parent was explicitly described as a nonpeptide secretagogue (Patchett et al., PNAS 1995). Calling it “peptidomimetic” is a fair interpretation of the structure; calling it a peptide is not.
Why is it called MK-777?
We could not find a published source for the “MK-777” code or the name “acetamoren,” and the code should not be confused with MK-0777, which PubChem lists as a different, unrelated compound (TPA023, CID 9908684). Our interpretation is that “MK-777” echoes the parent’s MK-0677 code. Either way, the reliable identifier is CAS 950841-87-9.
How can a lab tell MK-777 and ibutamoren apart?
Because the two molecules differ by a single acetyl group, the cleanest distinction is mass. Using PubChem’s monoisotopic exact masses, MK-777 sits at 570.2512 Da and ibutamoren at 528.2406 Da, a gap of 42.0106 Da, which is the mass of one C2H2O unit. High-resolution mass spectrometry resolves that difference easily. A few other practical points follow from the structure:
- Retention behavior. The slightly higher XLogP (1.6 versus 1.3) suggests MK-777 would elute a little later than ibutamoren on a reversed-phase column. That is an interpretation from computed values, not a measured result.
- Free amine test. Ibutamoren has a free primary amine; MK-777 does not. In principle, amine-reactive reagents should therefore respond to the parent and not to the acetylated form, which can flag contamination by the parent.
- Chirality. PubChem’s IUPAC name places the single stereocenter in the (2R) configuration. A sample of the opposite configuration would have the same mass, so chiral identity needs its own check.
In short, mass confirms the acetyl group, and the CAS number, the InChIKey and the stereochemistry together confirm that the material matches the PubChem record.
How is MK-777 tested?
All applicable tests are performed on our products, and the certificates are posted publicly. Open the current MK-777 certificate of analysis. Because the name itself is not standardized, matching the COA’s identity results to the CAS number and the structure above is the most useful check.
How is MK-777 supplied for research?
Modern Aminos lists MK-777 (acetamoren) as a single laboratory reference material. See the MK-777 product page for the current listing and availability.
Where MK-777 sits among other research compounds
MK-777 is a small-molecule derivative, not a peptide or a receptor modulator of the SARM type. For other small molecules that get mislabeled as peptides, see is DADA a peptide and is bromantane a peptide. For a mitochondrial tool compound, see what BAM15 is.
Frequently asked questions
What is MK-777?
MK-777, also sold as acetamoren, is identified by CAS 950841-87-9, which PubChem files as N-acetyl ibutamorelin (C29H38N4O6S, 570.7 g/mol), an N-acetyl derivative of ibutamoren. It is supplied for laboratory research use only.
Is MK-777 the same as ibutamoren (MK-677)?
No. MK-777 carries an extra acetyl group on the terminal amine, which changes the formula from C27H36N4O5S to C29H38N4O6S.
Is MK-777 a SARM?
No. It does not target the androgen receptor. Its parent, ibutamoren, was described as a nonpeptide growth hormone secretagogue.
Is MK-777 a peptide?
No. It contains amino-acid-derived units, but its parent was described in the literature as a nonpeptide compound.
Is MK-777 the same as MK-0777?
No. PubChem lists MK-0777 as TPA023, an unrelated compound with a different structure.
How is MK-777 purity verified?
All applicable tests are performed on our products, and the current MK-777 certificate of analysis is posted publicly on the Modern Aminos COA page.
References
- Patchett AA, Nargund RP, Tata JR, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A. 1995;92(15):7001-7005. doi:10.1073/pnas.92.15.7001 (PMID 7624358)
- National Center for Biotechnology Information. PubChem Compound Summary for CID 57595228, N-Acetyl Ibutamorelin. pubchem.ncbi.nlm.nih.gov/compound/57595228
- National Center for Biotechnology Information. PubChem Compound Summary for CID 178024, Ibutamoren. pubchem.ncbi.nlm.nih.gov/compound/178024
MK-777 is best described by its CAS number: an N-acetyl derivative of ibutamoren with a well-defined structure and very little published biology of its own. Rely on the identifiers and the COA rather than the name.