What Is Ipamorelin?

Peptide Structure and Molecular Composition

Ipamorelin is a synthetic pentapeptide (5-amino-acid sequence) with the structural composition Aib-His-D-2-Nal-D-Phe-Lys-NH2. The peptide incorporates the non-standard residue α-aminoisobutyric acid (Aib) at the N-terminus, two D-amino acids (D-2-naphthylalanine in position 3 and D-phenylalanine in position 4), and features C-terminal amidation (Lys-NH2). This stereochemistry and the presence of non-standard amino acids distinguish ipamorelin from naturally occurring peptides and contribute to its biochemical properties.Review · PMID 18193177

The molar mass of ipamorelin is 711.85 Da, placing it in the molecular range of small peptides amenable to synthesis via standard solid-phase peptide synthesis methods. The molecular formula C38H49N9O5 reflects the specific elemental composition derived from its amino-acid sequence. The non-standard Aib residue at the N-terminus provides structural rigidity, while the D-amino acids contribute to the peptide's resistance to enzymatic degradation by common proteases. These structural modifications collectively influence the peptide's biophysical properties in aqueous solution and its interactions with biological receptors.Review · PMID 14610293Review · PMID 18193177

The three-dimensional structure of ipamorelin has been characterized through computational modeling and spectroscopic analysis described in peptide structural literature. The pentapeptide adopts a defined conformational structure in solution, stabilized by the D-amino acids and the Aib residue. This structural organization is critical for its specific recognition and binding to growth-hormone-releasing-peptide receptors. The compact 5-residue architecture represents a minimalist approach to receptor design, containing only the essential amino acids required for binding affinity.In vitro · PMID 41074841

Growth-Hormone-Releasing Peptide Receptor Recognition

Ipamorelin is characterized as a ligand for the growth hormone secretagogue receptor (GHSR), also known as the growth-hormone-releasing-peptide (GHRP) receptor. The peptide binds to this G protein-coupled receptor (GPCR) through specific molecular interactions involving the receptor's ligand-binding pocket. In-vitro biochemical assays measure binding affinity and activation through multiple biophysical and cell-based methods. Surface plasmon resonance and fluorescence-based binding assays quantify the dissociation constants and binding kinetics in cell-free systems.In vitro · PMID 35836065Review · PMID 18193177

Cultured cell systems expressing GHSR are used to characterize ipamorelin's receptor recognition and signaling activation. In-vitro cell-based assays measure receptor-ligand binding through competitive displacement assays and co-immunoprecipitation. Signaling activation downstream of GHSR engagement is measured through multiple readouts: intracellular calcium mobilization using fluorescent calcium indicators, phosphorylation of downstream kinases (ERK, Akt) by Western blotting, and gene-expression changes by quantitative PCR. These cultured cell studies characterize the biochemical basis of ipamorelin's receptor interaction in defined laboratory conditions.In vitro · PMID 41074841In vitro · PMID 35836065

The selectivity of ipamorelin for GHSR over related receptor subtypes has been examined through in-vitro binding and cellular assays comparing receptor activation across multiple GPCR targets. The pentapeptide structure provides specificity for GHSR through precise positioning of side chains within the receptor's binding pocket. Structural studies using site-directed mutagenesis of the receptor have identified key residues contributing to ipamorelin recognition. These structure-activity relationship investigations define the molecular basis for selective GHRP receptor engagement.In vitro · PMID 16020971Review · PMID 18193177

Biochemical and Analytical Characterization

Ipamorelin is chemically synthesized through solid-phase peptide synthesis (SPPS) and characterized through standard peptide analytical methods. High-performance liquid chromatography (HPLC) with reversed-phase separation and ultraviolet or mass-spectrometry detection establishes peptide purity and quantifies synthetic variants or impurities. Mass spectrometry analysis confirms the precise molar mass and verifies the intact 5-residue sequence. Amino-acid compositional analysis validates the presence of each residue in the correct stoichiometry.In vitro · PMID 35836065

Ipamorelin's peptide identity is confirmed through tandem mass spectrometry (MS/MS), which fragments the intact peptide and sequences the chain through the pattern of fragment masses. The presence of non-standard amino acids (Aib) and D-amino acids is confirmed through specialized mass spectrometry methods and chiral analysis. Nuclear magnetic resonance (NMR) spectroscopy provides conformational information about the peptide in solution, revealing the structural organization stabilized by the Aib and D-amino-acid residues. These analytical methods collectively verify the synthetic peptide's identity and purity.In vitro · PMID 41074841

Solution stability of ipamorelin is characterized through in-vitro degradation assays examining the peptide's resistance to proteolytic digestion. The peptide is exposed to crude enzyme preparations (blood plasma, cellular lysates, buffer containing protease cocktails) and quantified over time using liquid chromatography-mass spectrometry. The protective activity of the D-amino acids and Aib residue against protease digestion is demonstrated through comparison of degradation kinetics with fully L-amino-acid analogs. These stability characterizations inform storage conditions and research methods.In vitro · PMID 35836065In vitro · PMID 41074841

Peptide Design and Structure-Activity Relationships

Ipamorelin represents a minimalist structure-activity optimization for GHRP receptor recognition. Unlike longer peptide ligands such as sermorelin or growth-hormone-releasing hormone (GHRH), which are 29-44 residues long, ipamorelin achieves binding affinity through a compact pentapeptide architecture. This small peptide design strategy was developed through systematic variation of amino-acid sequences, testing each analog through binding assays and cultured cell signaling readouts. The identification of the critical pentapeptide sequence representing the minimal GHRP-active structure emerged from these systematic structure-activity relationship studies.Review · PMID 18193177Review · PMID 14610293

The incorporation of D-amino acids in ipamorelin was driven by structure-activity optimization for receptor selectivity and peptide stability. D-amino acids are not naturally incorporated into proteins and therefore confer resistance to proteolytic enzymes that specifically recognize L-amino-acid stereochemistry. The non-standard Aib residue contributes conformational rigidity, pre-organizing the peptide into a structure favorable for receptor binding. These design principles—minimizing peptide length, incorporating non-natural amino acids, and optimizing three-dimensional structure—represent strategies in peptide drug development.In vitro · PMID 41074841Review · PMID 18193177

Computational peptide design methods have been applied to GHRP peptides including ipamorelin analogs, using algorithms to predict which sequences will adopt structures compatible with GHSR binding. Structure-activity relationship databases cataloging the binding affinity of hundreds of ipamorelin variants, generated through chemical synthesis and in-vitro screening, have guided the design of optimized analogs. These computational and experimental approaches define the structure-function relationships linking the peptide's amino-acid sequence to its molecular recognition properties.In vitro · PMID 41074841

The studies at a glance

Representative in-vitro biochemical characterization approaches for ipamorelin and GHRP peptides

Frequently asked questions