MK-677 (Ibutamoren) Overview
MK-677, also known as ibutamoren and by the developmental designations MK-0677 and L-163,191, is a non-peptide, orally bioavailable agonist of the growth hormone secretagogue receptor (GHS-R1a). It was originally developed by Merck & Co. and has been studied extensively in published preclinical and clinical pharmacology research for its activation of the ghrelin receptor and downstream modulation of the growth hormone / IGF-1 axis.
MK-677 has been advanced through multiple Phase II clinical research investigations across a range of indications, and is widely cited as a reference non-peptide GHS-R1a agonist in endocrine pharmacology, signaling research, and analytical chemistry literature.
MK-677 is not approved for human or veterinary use and is supplied strictly for laboratory and analytical research purposes.
Mechanism of Action
MK-677 binds the growth hormone secretagogue receptor type 1a (GHS-R1a) and acts as a non-peptide ghrelin mimetic. Receptor activation produces sustained, pulsatile increases in growth hormone secretion and corresponding elevation of circulating IGF-1 in published preclinical and clinical pharmacokinetic studies.
Reported characterizations include:
- Selective non-peptide agonist at GHS-R1a
- Orally bioavailable in published rodent, primate, and human pharmacokinetic studies
- Sustained pulsatile growth hormone release with corresponding IGF-1 elevation
- Reported activity at GHS-R1a-expressing regions associated with appetite and metabolic regulation
- Minimal reported effect on serum cortisol in published clinical studies, distinguishing MK-677 from earlier non-selective GHS agents
MK-677 does not function as growth hormone itself; it acts upstream by stimulating endogenous GH release, which makes it a useful reference compound for studying GH axis regulation rather than direct GH receptor signaling.
Chemical Structure & Identification
- Chemical Name (mesylate): 2-Amino-N-[(2R)-3-(benzyloxy)-1-{1-methanesulfonyl-1,2-dihydrospiro[indole-3,4′-piperidin]-1′-yl}-1-oxopropan-2-yl]-2-methylpropanamide methanesulfonate
- Synonyms: MK-677; MK677; MK-0677; Ibutamoren; Ibutamoren mesylate; L-163,191; Crescendo
- CAS Number (mesylate salt): 159752-10-0
- CAS Number (free base): 159634-47-6
- Molecular Formula (mesylate): C₂₈H₄₀N₄O₈S₂
- Molecular Weight (mesylate): 624.77 g/mol
- PubChem CID: 11595109
- UNII: R90JB6QJ2B
Structural Description: MK-677 is a non-peptide small-molecule ghrelin receptor agonist built on a spiro[indoline-3,4′-piperidine] scaffold, with a methanesulfonyl group on the indoline nitrogen, a chiral (R)-configured 2-amino-isobutyramide group, and a benzyloxymethyl ether arm. The structure is supplied most commonly as the methanesulfonate (mesylate) salt, which contributes to oral bioavailability and crystallinity. Structural identification and molecular data are referenced against PubChem.
Physical and Chemical Properties
- Appearance: White to off-white crystalline powder
- Solubility: Soluble in DMSO and similar organic solvents; limited aqueous solubility
- Stability: Stable under dry, cool, light-protected storage conditions
- Recommended storage: -20 °C for long-term stability
Research Focus Areas
MK-677 is commonly referenced in laboratory research involving:
- GHS-R1a receptor binding, signaling, and transactivation studies
- Growth hormone / IGF-1 axis pharmacology research
- Non-peptide ghrelin mimetic structure-activity (SAR) analysis
- Comparative GHS pharmacology alongside related ghrelin receptor ligands (capromorelin, anamorelin, hexarelin, GHRP-2/6)
- In vitro metabolism, ADME, and pharmacokinetic research
- Analytical method development and reference-standard work
Research Use Disclaimer
MK-677 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
MK-677 (ibutamoren) is a structurally defined, well-characterized non-peptide growth hormone secretagogue receptor agonist with one of the deepest pharmacology and clinical research profiles in the GHS class. Its spiro[indoline-piperidine] scaffold, oral bioavailability, and detailed GH/IGF-1 axis modulation profile make it a widely used reference compound in controlled laboratory studies of ghrelin receptor signaling and endocrine pharmacology.
| CAS Number | 159634-47-6 |
| Other Names | MK-677; MK-0677; L-163,191; Oratrope |
| IUPAC Name | 2-amino-2-methyl-N-[(2R)-1-(1-methylsulfonylspiro[2H-indole-3,4′-piperidine]-1′-yl)-1-oxo-3-(phenylmethoxy)propan-2-yl]propanamide mesylate. |
| Molecular Formula | C₂₈H₄₀N₄O₈S₂ |
| Molecular Weight | 624.77 |
| Dry-Fill Capsule Concentration | 12.5mg |
| Liquid Concentration And Solution | 25mg/ml Propylene Glycol/ DMSO |
| Aliquot Concentration And Solution | 50mg/ml PEG400, Propylene Glycol, Benzyl Benzoate, Benzyl Alcohol |
