FGL

FGL is a synthetic pentadecapeptide (15 amino acids) with the sequence EVYVVAENQQGKSKA, corresponding to a specific functional region of the neural cell adhesion molecule (NCAM) that mediates NCAM's interaction with fibroblast growth factor receptor 1 (FGFR1). It was developed primarily through the research of Elisabeth Bock and Vladimir Berezin at the University of Copenhagen, derived directly from the sequence of human NCAM (UniProt entry P13591).

Chemically, FGL has molecular formula C71H116N20O25, molecular weight approximately 1,649.8 g/mol, CAS number 499993-62-3, PubChem CID 16200289. At Verified Peptides, we want to note that a related, longer, and specifically optimized peptide called FGLL was separately developed for clinical translation purposes — researchers should be aware that human safety data described below applies specifically to FGLL, not necessarily identically to the original 15-residue FGL sequence used in most of the preclinical research literature, even though the two are closely related NCAM-mimetic peptides from the same research program.

NCAM itself is a well-established, independently characterized cell-surface glycoprotein involved in cell-cell adhesion, particularly important during nervous system development and in adult synaptic plasticity. FGL's design strategy — isolating a specific, small functional peptide fragment responsible for one of NCAM's several distinct signaling interactions (its FGFR1-binding site specifically, as opposed to its other adhesion-related interactions) — is a genuinely elegant example of translating a complex cell-adhesion molecule's biology into a discrete, synthesizable peptide tool.

At Verified Peptides, we think FGL has a genuinely substantial, multi-paper preclinical research literature, primarily from the Bock/Berezin research program in Denmark, and we want to describe its full arc honestly, including its incomplete clinical translation. Beyond the mechanistic studies described above, FGL has been shown to promote early postnatal sensorimotor development and enhance social memory retention in rodents (PMID 16784819), and to rescue spatial learning and memory impairments in a rat model of neonatal phencyclidine treatment used to study schizophrenia-relevant cognitive deficits (PMID 19133297) — a genuinely diverse set of behavioral and cognitive research applications across development, aging, and disease-model contexts.

A related, specifically optimized peptide, FGLL, was advanced into real human clinical testing: a Phase 1 study (Anand et al., Clinical Pharmacokinetics, 2007, PMID 17375985) administered single intranasal doses of FGLL (25, 100, and 200 mg) to 24 healthy male volunteers in an open-label design, evaluating tolerability, safety, and pharmacokinetics — a genuine, real human safety trial, though a Phase 1 pharmacokinetic/tolerability study rather than an efficacy trial.

Subsequently, the Copenhagen-based biotechnology company Enkam Pharmaceuticals, in collaboration with the University of Copenhagen, secured a substantial European Union grant (reported as approximately 6 million euros) to advance FGL itself into human clinical testing for Alzheimer's disease, under a program called NeuroFGL. Secondary sources report that this program successfully demonstrated FGL was safe and well tolerated in human testing. We want to be direct about what has happened since: despite this reported positive safety outcome, we did not locate evidence of continued active clinical development, and secondary sources describe the program as having gone dormant, with FGL described as a stalled or dead-end asset for Enkam Pharmaceuticals rather than an actively progressing clinical candidate.

No FGL or FGLL formulation has received FDA approval for any indication. At Verified Peptides, we sell research-grade FGL exclusively for laboratory research, and we think its combination of a substantial, multi-institution-adjacent preclinical literature (though still concentrated within one primary research program), real human Phase 1 safety data for a closely related peptide, and an apparently stalled rather than failed clinical program makes it a genuinely distinctive case among the compounds in this catalog — neither a clear clinical success nor a clear clinical failure, but an incompletely resolved development story.

FGL's design strategy — isolating a single functional binding domain from a much larger, multi-functional cell-adhesion molecule (NCAM) and synthesizing it as a standalone peptide — represents a distinct engineering approach from most other peptides in this catalog, which are either naturally occurring standalone hormones or engineered analogs of naturally occurring standalone peptides, rather than functional fragments carved out of a much larger structural protein.

NCAM itself, the parent molecule FGL is derived from, has a considerably broader biological role than the single FGFR1-binding interaction FGL specifically mimics — NCAM is also involved in direct cell-cell adhesion through homophilic binding to NCAM on adjacent cells, and in interactions with other receptor systems beyond FGFR1. FGL's research value depends specifically on isolating just the FGFR1-relevant signaling from this broader, multi-functional parent molecule, which is both a strength (mechanistic precision) and a limitation (it does not reproduce NCAM's full range of biological activity). FGFR1 itself is independently well-characterized in mainstream cell biology beyond its NCAM-related role, playing important functions in embryonic development and tissue repair, and is notably a target of interest in oncology, where FGFR-pathway-targeting drugs have been developed for certain cancers — meaning FGL's mechanism connects to a receptor system with substantial independent research investment, even though FGL's own specific application (neural plasticity and memory) is quite distinct from the oncology contexts in which FGFR1 is more commonly discussed.

The distinction between FGL and FGLL (the extended peptide that actually completed human Phase 1 testing) is a genuinely important one for researchers to track carefully, since much of the accessible secondary literature discusses "FGL" and its clinical development somewhat interchangeably with FGLL — researchers relying on the human safety data specifically should confirm which exact peptide variant is under discussion in any given source.

The NeuroFGL program's apparent dormancy after reportedly demonstrating human safety and tolerability is a pattern worth noting for researchers evaluating early-stage biotech programs generally: a positive safety signal in early clinical testing does not guarantee continued funding, subsequent efficacy trials, or eventual approval, and many genuinely promising early-stage compounds do not progress further for reasons (funding, strategic prioritization, business decisions) unrelated to the compound's underlying scientific merit.

At Verified Peptides, we require independent third-party HPLC purity testing and mass spectrometry identity confirmation for every batch of research-grade FGL we offer, with a Certificate of Analysis (COA) available for each lot. As a 15-residue peptide, FGL can be synthesized to high purity using standard solid-phase peptide synthesis methods.

We source exclusively from manufacturers operating under Good Manufacturing Practice (GMP)-aligned quality systems, and every lot is independently verified rather than accepted solely on a supplier's internal documentation. Given the FGL/FGLL naming distinction discussed above, researchers should confirm exactly which specific peptide sequence and length they are receiving, since these are related but distinct compounds. Researchers should always request and review the specific COA for the lot they receive, confirming purity percentage and molecular identity before use in any experimental protocol.

Lyophilized FGL is stable when stored at -20°C, protected from light and moisture, and researchers can generally expect the unreconstituted peptide to maintain integrity over an extended period under these conditions. At Verified Peptides, we ship lyophilized peptide with appropriate cold-chain packaging to preserve stability in transit.

Once reconstituted with bacteriostatic water or another appropriate sterile diluent, FGL solution should be stored refrigerated at 2–8°C and used within the timeframe indicated on the product's documentation. As with other peptides in this catalog, reconstituted solutions are generally less stable than the lyophilized form and more susceptible to degradation and microbial contamination with repeated freeze-thaw cycling.

Researchers should avoid repeated freeze-thaw cycles of reconstituted material and should follow the specific storage guidance provided with each lot's documentation to preserve sample validity for research use.