spec sheet8 rows
PQCA A selective M1 positive allosteric modulator from Merck, used as the reference preclinical tool for the claim that boosting acetylcholine at M1 alone improves cognition without the gut effects of a cholinesterase inhibitor.
- Reverses scopolamine-induced memory and attention deficits in rats and macaques
- No gastrointestinal signs at procognitive doses in rhesus monkeys
- Additive with donepezil at doses that do nothing alone
- Selective for M1 over M2, M3 and M4 in the discovery assay
- Improves recognition memory in the Tg2576 amyloid mouse
- No human exposure and no human safety data
- Cholinergic tolerability was scored only as salivation and feces output
- Seizure and cardiovascular screening not reported
- Never advanced past preclinical work
Overview
The workhorse of the M1 PAM literature rather than a drug. Its value is the clean comparison it made possible: PQCA, donepezil and xanomeline, in the same monkeys, in the same task, scored for cognition and for salivation and stool in one experiment. That comparison is why the field kept funding M1 PAMs after xanomeline failed on tolerability. Nothing about the molecule was ever aimed at a human.
- Doses of PQCA and donepezil that each did nothing on their own improved paired associates learning in rhesus monkeys when given together; that combination result is the argument for adding an M1 PAM on top of a cholinesterase inhibitor rather than replacing it.
- PQCA raised blood flow in the frontal cortex of mice at the same plasma concentrations that improved behavior in rats and in two macaque species, and that imaging readout was proposed as the way to pick a human dose that was never picked.
Mechanism
PQCA binds an site on the M1 receptor and raises the receptor's response to rather than activating it directly. In calcium mobilization assays it potentiated acetylcholine at human M1 with an inflection point near 135 nM, and at rat, mouse and rhesus M1 near 89, 69 and 49 nM; at 10 micromolar in the same assay format it scored as not active at M2, M3 and M4 [5]. Because potentiation only appears where is already being released, the effect follows endogenous cholinergic tone in and instead of switching on every subtype at once.
In mice it raised frontal cortical blood flow at plasma concentrations close to the ones that worked behaviorally, which the authors put forward as a translational biomarker for choosing a clinical dose [3]. The published PQCA work reports potency and in vivo margins; it does not report a fitted cooperativity value, so where PQCA sits on the alpha scale that later separated the Takeda compounds is not established.
receptor fingerprint
M1 (CHRM1)Positive Allosteric Modulator
M2, M3 and M4 (CHRM2, CHRM3, CHRM4)Not active at 10 micromolar in the same calcium assay
Safetyrisks and cautions, not medical advice
No human has been dosed with PQCA, so human tolerability is unknown and everything here is animal data. The reason the compound is cited so often is the rhesus comparison: donepezil and xanomeline each produced salivation and increased feces output at doses at or below a fivefold margin from their minimum procognitive dose, whereas PQCA produced no gastrointestinal effects across the same dose range [2]. That study defined cholinergic tolerability as salivation and feces output, which is a narrow window, and it is a clean result in one species across one range of doses rather than a general clearance for M1 potentiation [2]. The rhesus touchscreen work that followed scored memory and attention and did not screen for seizure, cardiovascular effects or repeat-dose toxicity, so nothing about those risks can be drawn from it [1].
History
Discovered at Merck Research Laboratories in West Point, Pennsylvania, from a quinolizidinone carboxylic acid series built on earlier quinolone carboxylic acid M1 modulators; it appears as modulator 4i in the 2011 scaffold paper, picked for high plasma free fraction and central nervous system exposure [5]. Between 2012 and 2015 the same group ran it through rat novel object recognition, cynomolgus self-ordered spatial search, rhesus object retrieval detour, rhesus paired associates learning and continuous performance, and the Tg2576 amyloid mouse. The published record on it is entirely preclinical.
Reputation
Regarded inside the muscarinic field as the reference M1 PAM tool rather than a candidate drug; when a study needs to show that M1 potentiation specifically produces a cognitive effect, PQCA is a common choice. Outside pharmacology it is essentially unknown. The acronym is also a poor search term, because the same four letters denote unrelated pyridine-quinoline carboxylic acid ligands in coordination chemistry, which dominate a bare literature search for the name.
Subjective profileweighing the evidence above
The workhorse of the M1 PAM literature rather than a drug. Its value is the clean comparison it made possible: PQCA, donepezil and xanomeline, in the same monkeys, in the same task, scored for cognition and for salivation and stool in one experiment. That comparison is why the field kept funding M1 PAMs after xanomeline failed on tolerability. Nothing about the molecule was ever aimed at a human.
Resources
This entry is here for reference.
Research
- 2011first citedDiscovery of a selective allosteric M1 receptor modulator with suitable development properties…
- 2015most recentThe selective positive allosteric M1 muscarinic receptor modulator PQCA attenuates learning and…
- 1.The M1 Muscarinic Positive Allosteric Modulator PQCA Improves Performance on Translatable Tests of Memory and Attention in Rhesus Monkeys
- 2.Improved cognition without adverse effects: novel M1 muscarinic potentiator compares favorably to donepezil and xanomeline in rhesus monkey
- 3.The muscarinic M1 receptor positive allosteric modulator PQCA improves cognitive measures in rat, cynomolgus macaque, and rhesus macaque
- 4.The selective positive allosteric M1 muscarinic receptor modulator PQCA attenuates learning and memory deficits in the Tg2576 Alzheimer's disease mouse model
- 5.Discovery of a selective allosteric M1 receptor modulator with suitable development properties based on a quinolizidinone carboxylic acid scaffold
5 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
Can I buy PQCA as a nootropic?
No. It is a preclinical research compound with no human exposure, no established dose and no legitimate consumer supply; anything sold under the name should be treated as an unidentified substance.
How is an M1 PAM different from a drug like donepezil?
Donepezil raises acetylcholine everywhere by blocking its breakdown, which reaches every muscarinic and nicotinic subtype including the ones in the gut and heart. A PAM does not activate anything by itself; it makes the M1 subtype respond more strongly to whatever acetylcholine is already present, so the effect is confined to where and when M1 is actually being used.
Did PQCA reach human trials?
The published record on PQCA covers rats, mice, cynomolgus macaques and rhesus macaques, and that is where it stops. The animal work was built to justify testing the M1 PAM idea in patients, not to carry this particular molecule forward.
Why does the name return chemistry papers instead of pharmacology?
Because the abbreviation is not unique. Coordination chemists use the same letters for a pyridine-quinoline carboxylic acid ligand. Searching for the full quinolizinone carboxylic acid name, or for the synonym MSD-M1PAM, gets to the muscarinic literature faster.
Adverse effects
- No human exposure and no human safety data
- Cholinergic tolerability was scored only as salivation and feces output
- Seizure and cardiovascular screening not reported
- Never advanced past preclinical work