Tripeptide
A tripeptide is a chain of three amino acids linked by two peptide bonds. This category concentrates several of the most studied bioactive peptides in biochemistry history, starting with glutathione (γ-L-glutamyl-L-cysteinyl-glycine), a major intracellular antioxidant present in all aerobic cells, essential for reactive species detoxification and cellular redox cycles.
Other notable natural tripeptides include TRH (thyrotropin releasing hormone, pyroGlu-His-Pro-NH₂), a hypothalamic hormone that stimulates TSH and prolactin release from the pituitary, extensively studied in neuromodulation research. Isoleucyl-prolyl-proline (IPP) and valyl-prolyl-proline (VPP), derived from milk casein, are studied for ACE (angiotensin-converting enzyme) inhibitory properties in cardiovascular research.
RGD tripeptides (arginine-glycine-aspartate) constitute a universal recognition motif for cellular integrins, opening massive research avenues in adhesion biology, tumor targeting and biomaterial development. Glycyl-histidyl-lysine (GHK), the copper-binding peptide, is explored in skin regeneration research and extracellular microenvironment modulation.
Like dipeptides, tripeptides benefit from excellent intestinal absorption via PepT1 and good membrane permeability. They represent an optimal compromise between biological activity (sufficient to engage receptors), bioavailability (intact absorption possible) and chemical stability (fewer vulnerable sites than long chains).
In SPPS synthesis, tripeptides are short targets achievable within hours and often serve as optimization models before moving to longer sequences. In a research catalog, they appear mainly as affinity motifs, targeted inhibitors or reference products for in vitro pharmacology protocols.
Most documented research tripeptides include: GHK (Gly-His-Lys, 340 Da) and its copper complex GHK-Cu, discovered by Pickart in 1973 in human plasma, with documented skin regenerative properties; TRH (pyroGlu-His-Pro-NH2, thyrotropin-releasing hormone); Ac-SDKP (Ac-Ser-Asp-Lys-Pro) N-acetylated thymosin β-4 metabolite with anti-fibrotic activity; reduced glutathione (γ-Glu-Cys-Gly) major intracellular antioxidant; carnosine (β-Ala-His) and anserine (β-Ala-Me-His) neuromuscular buffers.
In SPPS synthesis, a tripeptide is produced in 3 successive Fmoc coupling cycles on resin (Rink Amide or Wang depending on desired C-terminal), typically in 4-6 hours for complete sequence. Synthetic yield reaches 80-95% after preparative RP-HPLC purification. Monoisotopic molecular mass of an unmodified tripeptide lies between 250 and 500 Da depending on residue size. Structural analysis by 1D or 2D ¹H NMR (COSY, TOCSY, NOESY) confirms sequence and identifies dominant solution conformations. Tripeptides easily cross cell membranes by passive transport or via PepT1/PepT2 transporters, making them preferred pharmacological tools for intracellular research.