RESEARCH MONOGRAPH · KDC-MN-1355

GTS-21

May 10, 2026 Kodiac biolabs Research Revised May 22, 2026 3 min read

Our opinion on this compound

67/100

The marine-alkaloid-derived alpha-7 partial agonist that started the modern alpha-7 era. Cross-reactivity matters

GTS-21 (also DMXB-anabaseine) is the alpha-7 nicotinic partial agonist that essentially launched the modern era of alpha-7 receptor pharmacology. The compound is a synthetic derivative of anabaseine, a marine alkaloid from worms in the genus Amphiporus, and Bill Kem's group at the University of Florida did the chemistry in the 1990s. It was the first reasonably selective alpha-7 partial agonist with decent CNS penetration, and most of the early evidence that alpha-7 was a viable cognitive enhancement target came from GTS-21 work.

The mechanism is partial agonism at alpha-7 with significant cross-reactivity at alpha-4-beta-2 nAChRs. That cross-reactivity is both the historical feature and the current liability. In the era before more selective compounds (encenicline, bradanicline, the PAMs), GTS-21 was the available tool. Now that we have selective compounds, the cross-reactivity is a confound for clean alpha-7 mechanistic studies.

The clinical data is interesting. Phase 2 trials in schizophrenia cognition by Targacept and others showed positive signal on attention and working memory measures, particularly in nonsmoking patients (which makes mechanistic sense given nicotine's effects on the same receptor systems). The Olincy schizophrenia work at Colorado was particularly influential. The Alzheimer's data was less clear.

What we like is the historical depth of the GTS-21 literature. There are more published mechanism-of-action studies, electrophysiology recordings, and animal cognition studies on this compound than on almost any other alpha-7 agonist. As a reference tool for alpha-7 pharmacology, GTS-21 has the deepest data backstop.

What we don't like is the alpha-4-beta-2 cross-reactivity. For studies that want to isolate alpha-7 mechanism, GTS-21 is no longer the cleanest tool. Encenicline, bradanicline, and the PAMs all have better selectivity. GTS-21 is still useful for replication of legacy studies and for situations where you specifically want some alpha-4-beta-2 activity, but as a clean alpha-7 probe it's been surpassed.

The metabolite story matters here too. 4-OH-GTS-21 is an active metabolite that contributes substantially to in vivo activity, and depending on dosing route, the parent versus metabolite contribution to receptor effects shifts. Plasma protein binding is also non-trivial.

Sourcing is small-molecule chemistry, NMR and HPLC standard, reputable vendors deliver above 95% purity. For alpha-7 historical work or studies that benefit from the cross-reactivity, GTS-21 has a place in the toolkit.

Evidence: 65
Mechanism: 72
Reliability: 68
Safety: 70
Sourcing: 78
Value: 70
Signal: 60
Staying power: 55

Alpha-7 nicotinic acetylcholine receptor partial agonist with alpha-4-beta-2 cross-reactivity, derivative of marine alkaloid anabaseine

A 3-(2,4-dimethoxybenzylidene)anabaseine derivative of the marine nemertine-worm alkaloid anabaseine, characterized in the laboratory of William Kem at the University of Florida and advanced through Phase 1 and Phase 2 clinical development for schizophrenia cognitive impairment, Alzheimer disease, and selected exploratory cognitive endpoints. The longest-studied alpha-7 nicotinic partial agonist in cognitive applications and the principal historical reference compound for the receptor class.

Abstract

GTS-21 (also known as DMXBA, DMBX-anabaseine, and 3-(2,4-dimethoxybenzylidene)anabaseine) is a small-molecule partial agonist of the alpha-7 subtype of the neuronal nicotinic acetylcholine receptor. The compound is a synthetic derivative of the natural product anabaseine, a marine alkaloid originally isolated from nemertine ribbonworms and characterized in the laboratory of William Kem at the University of Florida beginning in the late 1970s. The 3-(2,4-dimethoxybenzylidene) substitution increases alpha-7 nicotinic selectivity over the muscle-type receptor and produces the partial agonist functional profile that has supported clinical development. Functional intrinsic activity at human alpha-7 nicotinic receptors is approximately 30 to 50 percent of the acetylcholine maximum response. The compound is the longest-studied alpha-7 nicotinic partial agonist in cognitive applications. The compound was advanced through Phase 2 schizophrenia (Olincy 2006 proof-of-concept positive; Olincy 2017 confirmatory negative), Phase 2 Alzheimer disease (modest signals), and Phase 1 healthy volunteer cognition (Kitagawa 2003 positive at 50 mg). The compound is metabolized to two principal active metabolites (4-OH-GTS-21 and 2-OH-GTS-21) that retain alpha-7 partial agonist activity and contribute to dose-response complexity. The compound is not in active commercial development as of the most recent monograph revision; research-grade material is widely available and continues as a reference alpha-7 partial agonist tool.

Mechanism of action

Orthosteric partial agonism at the alpha-7 nicotinic acetylcholine receptor with intrinsic activity 30-50 percent of acetylcholine maximum, plus alpha-4-beta-2 cross-reactivity (partial agonism or antagonism depending on assay). Active metabolites 4-OH-GTS-21 and 2-OH-GTS-21 retain alpha-7 partial agonist activity and contribute to total receptor exposure.

Reported research dose ranges

Phase 2 schizophrenia: 75-150 mg three times daily by oral administration. Phase 1 healthy volunteer: single oral doses 25-150 mg with peak cognitive effect at 50 mg. Research applications: in vitro 0.1-30 micromolar; rodent in vivo 1-30 mg/kg.

Selected references

Kem WR. The brain alpha-7 nicotinic receptor may be an important therapeutic target for the treatment of Alzheimer disease: studies with DMXBA (GTS-21). Behav Brain Res. 2000;113(1-2):169-181.
Kitagawa H et al. Safety, pharmacokinetics, and effects on cognitive function of multiple doses of GTS-21 in healthy male volunteers. Neuropsychopharmacology. 2003;28(3):542-551.
Olincy A et al. Proof-of-concept trial of an alpha-7 nicotinic agonist in schizophrenia. Arch Gen Psychiatry. 2006;63(6):630-638.
Kem WR et al. Hydroxy metabolites of the Alzheimer drug candidate 3-[(2,4-dimethoxy)benzylidene]-anabaseine dihydrochloride (GTS-21): their molecular properties, interactions with brain nicotinic receptors, and brain penetration. Mol Pharmacol. 2004;65(1):56-67.
Olincy A et al. Pharmacokinetic limitations on effects of an alpha-7 nicotinic receptor agonist in schizophrenia: randomized trial with an extended-release formulation. Neuropsychopharmacology. 2017;42(6):1219-1224.

Read the full monograph

The full reference document covers compound identification with chemistry and synthesis, discovery and developmental history, mechanism of action across molecular targets with quantitative receptor pharmacology, comprehensive pharmacokinetics, indication-by-indication clinical evidence base, reported research dose ranges, sourcing and quality verification, reconstitution and handling, stack interaction considerations, adverse event signal, and a structured comparative assessment of five alpha-7 nicotinic acetylcholine receptor candidates judged against five competency standards. Embedded inline below; download for offline reading.

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GTS-21

Abstract

Mechanism of action

Reported research dose ranges

Selected references

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

Selected references

Read the full monograph

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