IDRA-21 (7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide) is a first-generation ampakine, a benzothiadiazine derivative and a congener of aniracetam. It is a positive allosteric modulator (PAM) of AMPA receptors, developed as a cognitive enhancer and widely used as a benchmark compound in research on AMPA-mediated synaptic plasticity.
Mechanism of Action
AMPA receptors are ionotropic glutamate receptors (GluA1–GluA4 subunits) responsible for fast excitatory synaptic transmission. After glutamate binds, the AMPA receptor rapidly desensitizes — temporarily ceasing to respond even in the presence of agonist. IDRA-21, an analog of cyclothiazide, binds to the receptor and inhibits this desensitization: the receptor stays open longer and the excitatory post-synaptic current (EPSC) is prolonged in its decay time. The result is enhanced excitatory synaptic transmission and facilitated long-term potentiation (LTP), the cellular correlate of learning and memory. IDRA-21 does not activate the receptor on its own — it is a modulator, not an agonist. Unlike cyclothiazide, it crosses the blood-brain barrier far more readily and is orally active.
Ampakine Class and Comparison to Aniracetam
Both IDRA-21 and aniracetam attenuate AMPA receptor desensitization, but IDRA-21 is 10–30× more potent at reversing cognitive deficits induced by alprazolam or scopolamine. IDRA-21 is regarded as the historical AMPA-PAM benchmark from which later, more potent ampakines (CX-516, CX-717, TAK-653) were developed. A key advantage: at cognition-enhancing doses IDRA-21 is virtually devoid of the neurotoxicity and convulsant liability seen with direct AMPA agonists.
Primate Studies
Thompson et al. (PNAS, 1995) showed that in patas monkeys, IDRA-21 (3 or 5.6 mg/kg p.o.) and aniracetam (30 mg/kg p.o.) — having no effect on behavior when given alone — significantly attenuated the learning deficit induced by alprazolam in a complex behavioral task. In separate work in rhesus monkeys on a delayed matching-to-sample (DMTS) task, IDRA-21 improved accuracy in aged animals by roughly 18%, supporting the hypothesis of using AMPA modulators to enhance cognition.
Cognitive Effects
In rodents, IDRA-21 improves spatial memory and learning, enhances hippocampal LTP, and facilitates glutamatergic transmission via GluA1/GluA2. It is orally active; in preclinical work cognitive effects were seen across a 0.15–10 mg/kg dose range. Effects appear not only in models of drug-impaired memory but also in normal animals.
Physicochemical Properties
Molecular weight: 232.69 g/mol. PubChem CID: 3688. Appearance: white to off-white crystalline powder. IUPAC: 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (S,S-dioxide). Soluble in DMSO (≥250 mg/mL, ultrasonication needed); poorly soluble in water.
Storage
The powder is stable at room temperature in a dry, dark place and tolerates ordinary shipping without refrigeration. For long-term storage (months–years), −20°C in an airtight container protected from moisture and light is optimal. DMSO solutions should be aliquoted and stored at −20°C.
BIOLABCHEMICALS