Ouabain API is a naturally occurring cardenolide cardiac glycoside obtained historically from Strophanthus gratus and related plants of the Apocynaceae family. It is also known as ouabaine, g-strophanthin, gamma-strophanthin, strophantine and acocantherine. PubChem identifies anhydrous Ouabain with CAS No. 630-60-4, molecular formula C29H44O12, and molecular weight 584.7 g/mol.
A major point for API identification is that Ouabain is frequently supplied as Ouabain Octahydrate. The octahydrate has CAS No. 11018-89-6, molecular formula C29H60O20, and molecular weight 728.8 g/mol. Therefore, the anhydrous and octahydrate forms should not be assigned the same molecular weight or CAS number in CMS data.
PubChem describes Ouabain as a cardioactive glycoside consisting of rhamnose and ouabagenin and identifies inhibition of the Na⁺/K⁺-transporting ATPase as a principal biological activity.
Ouabain is a structurally complex steroidal glycoside containing a cardenolide nucleus linked to a sugar moiety. The anhydrous compound has 29 carbon atoms, 44 hydrogen atoms and 12 oxygen atoms. PubChem reports an exact mass of 584.28327683 Da, XLogP3 of −1.7, 8 hydrogen-bond donors, 12 hydrogen-bond acceptors, and topological polar surface area of 207 Ų.
The octahydrate contains eight molecules of water of crystallization and consequently has the formula C29H60O20 and molecular weight 728.8 g/mol. PubChem reports an exact mass of 728.36779430 Da, 16 hydrogen-bond donors, 20 hydrogen-bond acceptors, 4 rotatable bonds, and topological polar surface area of 215 Ų for the octahydrate representation.
Ouabain is a potent inhibitor of the Na⁺/K⁺-ATPase membrane pump. Binding to this transporter interferes with active sodium and potassium transport across the cell membrane and can alter intracellular sodium and calcium concentrations. Its cardiotonic activity historically led to its use in cardiac medicine, while its ability to inhibit Na⁺/K⁺-ATPase has made it a widely used research compound in cell biology and pharmacology.
Research applications include:
For commercial and laboratory API documentation, Ouabain Octahydrate deserves separate treatment. Thermo Scientific/Fisher Scientific lists the octahydrate as CAS 11018-89-6, formula C29H44O12·8H2O, molecular weight 728.78 g/mol, white material, and a melting point of 260°C. A cited Thermo specification lists minimum 95% HPLC assay and specific rotation of −33.00° at 20°C, c = 1, H2O, on dry substance.
Another Thermo Scientific specification for Ouabain octahydrate reports ≥94.0% UV/Vis assay and 14.5–22.0% loss on drying, demonstrating why a particular commercial specification should be identified rather than treating every research-grade specification as a universal API standard.
Ouabain octahydrate is generally described as a white to off-white/pale yellow powder or crystalline material. Thermo/Fisher data report an authentic infrared spectrum and a melting point of 260.0°C. The same specification gives 95% minimum HPLC assay and specific rotation of −33.00° under the stated conditions.
For API quality-control purposes, analytical characterization can include HPLC/UV assay, IR identification, specific rotation, water/loss-on-drying determination and impurity profiling. However, publicly available sources do not establish one universally applicable numerical pharmaceutical release specification for every Ouabain API form. Accordingly, values below are clearly separated between verified chemical data and published commercial/reference specifications.
A pharmaceutical or research-grade Ouabain API dossier may include:
For CMS purposes, the hydrate state must always be stated because Ouabain anhydrous and Ouabain octahydrate have substantially different molecular weights and different CAS identifiers.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | ≤ 0.5% |
| Total Impurities | ≤ 1.5% |
| Water Content | NMT 0.5% |