Catalogue / MK-677
MK-677
Also written as Ibutamoren, Ibutamoren mesylate, L-163,191.
A spiroindoline sulfonamide that acts as a growth hormone secretagogue at the ghrelin receptor, supplied almost universally as the mesylate salt rather than as the free base shown here.
| Molecular formula | C27H36N4O5S |
| Average mass | 528.66 Da |
| Monoisotopic mass | 528.2406 Da |
| Molecular target | Ghrelin receptor, GHS-R1a |
| Electrospray polarity | Positive |
| Class | Non-androgenic compounds sold in the same category |
| Determination | Small molecule analysis, catalogue compound |
| Price | 267 USD |
Computed at build time from the composition shown on this page, not transcribed from a supplier datasheet.
MK-677 has an average molecular weight of 528.66 daltons and a monoisotopic mass of 528.2406 daltons, computed from the molecular formula C27H36N4O5S. Identity is confirmed by matching the measured mass against a certified reference standard, and purity is reported separately by reversed-phase chromatography at the compound's own ultraviolet maximum rather than at the 214 nm used for peptides. Neither figure states which enantiomer is present, which is a third determination on a chiral stationary phase.
| Ion | m/z |
|---|---|
| [M+H]+ | 529.2479 |
| [M-H]- | 527.2334 |
Usable response for this compound is in positive mode. The other ion is given because it is the one a wrongly configured method looks for.
A molecule of this size does not produce the multiply charged envelope a peptide does. It produces one singly charged ion, and which polarity that ion appears in is decided by the functional groups rather than by convenience. A nitro or cyano aromatic responds in negative mode; a basic amine responds in positive.
That is why a screen acquired in a single polarity misses part of its own compound list, and why a non-detect from such a screen is not evidence that a substance is absent. The polarity used belongs on the certificate alongside the result.
| The formula and masses on this page are the free base at 528.7 daltons. The mesylate salt as supplied is 624.8 daltons, so 25 milligrams of the salt delivers 21.2 milligrams of ibutamoren. That is a 15 percent difference that no purity figure shows and that only appears if the salt form is stated on the certificate. |
| It is not an androgen receptor ligand and is not a SARM. It is in this catalogue because it is sold and submitted alongside them, and because it is one of the substances most often found in products labelled as something else. |
| The free base ionises strongly in positive mode. A screen optimised in negative polarity for the aryl propanamides will not see it, which is the practical cost of treating a marketing category as an analytical one. |
Every compound fails in its own way. A generic peptide method applied without regard to these specifics produces a number that looks like a result and is not one.
A PPAR delta agonist pair, two REV-ERB agonists and a growth hormone secretagogue. All are sold as SARMs and none binds the androgen receptor. The distinction is not pedantry: it is the reason a single method tuned for the aryl propanamides under-reports every compound in this group, and the reason a class screen has to be built from the chemistry rather than from the marketing category.
LC-MS identity against a certified reference standard, with source and polarity chosen per compound because this group spans a basic amine, two neutral thioethers and two nitro heterocycles. Purity by HPLC-UV at the compound's absorbance maximum. The nitro compounds are handled under light protection, because their reduction product is a different molecule at a different mass.
Where the delivered milligram figure matters rather than the percentage, assay against a certified reference standard gives content directly, and where no such standard exists quantitative NMR against a certified internal standard gives an absolute purity that needs no standard of the analyte at all.
| LC-MS identity | Measured mass |
| HPLC-UV purity | Area at the UV maximum |
| Enantiomeric purity | Chiral stationary phase |
| Water content | Karl Fischer |
| Elemental impurities | ICP-MS |
| Residual solvents | GC-MS |
What is the molecular weight of MK-677?
The average molecular weight is 528.66 daltons and the monoisotopic mass is 528.2406 daltons, computed from the molecular formula C27H36N4O5S shown on this page. Both figures are calculated rather than transcribed, so they can be checked against the stated composition.
How is MK-677 tested for purity and identity?
LC-MS identity against a certified reference standard, with source and polarity chosen per compound because this group spans a basic amine, two neutral thioethers and two nitro heterocycles. Purity by HPLC-UV at the compound's absorbance maximum. The nitro compounds are handled under light protection, because their reduction product is a different molecule at a different mass. Purity is an area ratio measured at the compound's own ultraviolet maximum, and it describes the chromatographable fraction only. It says nothing about which enantiomer is present, because mirror images are not separated by an achiral column.
What goes wrong when MK-677 is analysed?
The formula and masses on this page are the free base at 528.7 daltons. The mesylate salt as supplied is 624.8 daltons, so 25 milligrams of the salt delivers 21.2 milligrams of ibutamoren. That is a 15 percent difference that no purity figure shows and that only appears if the salt form is stated on the certificate.
What does MK-677 analysis cost at ANALYTON?
Small molecule analysis, catalogue compound is priced at 267 US dollars, covering the determinations described on this page. Content, safety and elemental determinations are ordered alongside and are priced separately on the price list.
Updated 2026-09-01. Masses computed at build, not transcribed.