What is GB-115?

GB-115 (N-(6-phenylhexanoyl)glycyl-L-Tryptophan amide, also called GB115, Ranquilon, and N-(1-oxo-6-phenylhexyl)glycyl-L-Tryptophanamide; CAS 678996-63-9) is a synthetic N-acylated dipeptide amide. It is a cholecystokinin (CCK) receptor antagonist reference compound designed from the structure of cholecystokinin tetrapeptide (CCK-4, Trp-Met-Asp-Phe-NH₂). GB-115 is a peptide in the chemical sense: Glycine and L-Tryptophan are joined by a single peptide bond, the N-terminus is capped with 6-phenylhexanoic acid, and the C-terminus is a primary amide. Its activity in the published literature comes from two aromatic pharmacophores, a phenyl ring and an indole ring, held at the same spacing they have in CCK-4.

Its design route is documented by the group that created it at the V.V. Zakusov Research Institute of Pharmacology. Applying the topochemical principle to CCK-4 gave the retro sequence Phe-Asp-Met-Trp-NH₂; the two internal residues were replaced with a Gly-Gly spacer, and the Phe-Gly fragment was then replaced with a topologically equivalent 6-phenylhexanoyl group to increase biological stability, keeping the phenyl-to-indolyl distance of the parent peptide. In the homolog series, shortening that distance by a single CH₂ group gave a tenfold decrease in activity (Gudasheva et al., 2018, PMC6302556). That is what GB-115 does at the molecular level: it presents the CCK-4 pharmacophore pair on a capped, two-residue backbone.

Batch-verified at Modern Aminos, GB-115 is supplied in three laboratory formats:

• 2.5 mg capsules, 60 units
• 5 mg/mL liquid, 30 mL precision dropper
• 2 mg/mL atomizer, 5 mL premixed atomizer

Laboratories building neuropeptide-receptor and peptide-design assay panels often place GB-115 next to other public reference listings such as Vilon, Pinealon, Dihexa, and TAK-653, as well as Selank and Noopept. For a closer look at whether GB-115 is a peptide, see Is GB-115 a Peptide? N-(6-Phenylhexanoyl)glycyl-L-Tryptophan Amide Explained.

Chemical and Molecular Data for GB-115

Identity fields are drawn from PubChem CID 11281948; purity and quantity values come from the lot certificates in the Certificate of Analysis tab.

What are the Mechanisms of Action?

The biochemical targets and design logic of GB-115 in laboratory research include:

• Cholecystokinin receptor antagonism: CCK1 and CCK2 receptors are G protein-coupled receptors for cholecystokinin and gastrin peptides (Dufresne et al., 2006). GB-115 is described as a short peptide antagonist of CCK2 receptors (Kolik et al., 2007) and, in later work, as having CCK1-receptor antagonist properties (Panchenko et al., 2025). No radioligand K_i or IC₅₀ for either subtype is indexed in PubMed.
• Retro-analog (topochemical) design from CCK-4: The topochemical principle holds that an L-amino-acid peptide written in reverse order can keep the same spatial arrangement of side chains as the same sequence built from D-amino acids. Applied to CCK-4 (Trp-Met-Asp-Phe-NH₂), it gave the retro sequence Phe-Asp-Met-Trp-NH₂, which was then condensed step by step into GB-115 (Gudasheva et al., 2018).
• Phenyl–indolyl pharmacophore spacing: The two internal residues were replaced with a Gly-Gly spacer, and the Phe-Gly fragment was replaced with a topologically equivalent 6-phenylhexanoyl group, keeping the native distance between the phenyl (Phe) and indolyl (Trp) groups. In the GB-115 homolog series, shortening that distance by one CH₂ group gave a tenfold decrease in activity (Gudasheva et al., 2018).
• Type II β-turn as the active conformation: ¹H NMR conformational analysis in solution, nuclear Overhauser effect data, and sterically restricted analogs identified a type II β-turn as the biologically active conformation of GB-115 (Gudasheva et al., 2013).
• L-Tryptophan stereocenter: GB-115 has one defined stereocenter, the (2S) α-carbon of L-Tryptophan, encoded in InChIKey ZBIQNIJICMOVKN-QFIPXVFZSA-N (PubChem CID 11281948). In the 2007 design series, the L-Tryptophan and D-Tryptophan members showed opposite activity profiles (Gudasheva et al., 2007), and later modeling showed pharmacophoric similarity between the D-enantiomer and CCK-4 (Gudasheva et al., 2018).
• N-acyl cap and C-terminal amide chemistry: The 6-phenylhexanoyl cap was chosen to increase biological stability relative to a peptide fragment (Gudasheva et al., 2018), and the C-terminal primary amide matches the amidated C-terminus of CCK-4. PubChem computes XLogP3 3 and TPSA 117 Ų for GB-115 versus XLogP3 −2.1 and TPSA 235 Ų for CCK-4 (PubChem CID 446569).

What Does Published Research Show for GB-115?

Peer-reviewed literature on GB-115 and its parent peptide CCK-4 centers on peptide design, conformational analysis, synthesis, and receptor classification:

• Design from CCK-4 (PMC): An open-access review from the V.V. Zakusov Research Institute of Pharmacology walks through the GB-115 design: topochemical retro-inversion of CCK-4, a Gly-Gly spacer, and replacement of the Phe-Gly fragment with a 6-phenylhexanoyl group to give C₆H₅(CH₂)₅CO-Gly-Trp-NH₂ (PMC6302556).
• Design and synthesis of the dipeptide series (PubMed): The 2007 series Ph(CH₂)_nCO-NH(CH₂)_mCO-Trp-NH₂ (n = 1, 3–5; m = 1–3) was designed from CCK-4 by the Shemyakin–Ovchinnikov–Ivanov topochemical principle; GB-115 is the n = 5, m = 1 L-Tryptophan member (PubMed 17886432).
• Biologically active conformation (PubMed): ¹H NMR and nuclear Overhauser effect studies, backed by sterically restricted analogs, assigned a type II β-turn as the active conformation (PubMed 24397028).
• Five-step synthesis (Pharmaceutical Chemistry Journal): The optimized route runs from 6-phenylhexanoyl chloride (thionyl chloride), through acylation of Glycine at 0 °C and esterification of L-Tryptophan, to mixed-anhydride coupling with isobutyl chloroformate in dimethylformamide and final ammonolysis of the dipeptide ethyl ester with gaseous ammonia in methanol (DOI 10.1007/s11094-011-0569-z).
• Cholecystokinin receptor background (PubMed): CCK1 and CCK2 receptor structure, binding properties, and signaling pathways are reviewed in PubMed 16816139.
• Chemical Directory & Structure Verification (PubChem): PubChem CID 11281948 lists CAS 678996-63-9, formula C₂₅H₃₀N₄O₃, MW 434.5, exact mass 434.23179 Da, InChIKey ZBIQNIJICMOVKN-QFIPXVFZSA-N, UNII G5YT2F7SG8, and DSSTox DTXSID70461104 (PubChem 11281948).
• Analytical Quality: Why chromatographic testing matters for reference materials is covered in Modern Aminos’ note on HPLC testing.

How does GB-115 compare to other compounds?

To map cholecystokinin-receptor and peptide-design chemistry, researchers compare GB-115 against its parent peptide and other peptide-derived and small-molecule reference compounds, including several available at Modern Aminos:

Frequently Asked Questions (FAQs)