Voxelotor is a synthetic small-molecule pharmaceutical active ingredient that was developed as a hemoglobin S polymerization inhibitor for sickle cell disease. It acts directly on hemoglobin and was designed to increase hemoglobin's affinity for oxygen, thereby reducing hemoglobin S polymerization under deoxygenated conditions.
Voxelotor is also known by its development code GBT440. The chemical name of voxelotor is 2-hydroxy-6-((2-(1-isopropyl-1H-pyrazol-5-yl)pyridin-3-yl)methoxy)benzaldehyde. Its molecular formula is C₁₉H₁₉N₃O₃ and its molecular weight is 337.4 g/mol.
Voxelotor is a non-salt small molecule and exists as a crystalline free-base drug substance. FDA describes the drug substance as a white-to-yellow-to-beige compound in crystalline Form II. It is reported to be non-hygroscopic and highly soluble in common organic solvents such as acetone and toluene, while being insoluble in water.
The CAS Number associated with voxelotor is 1446321-46-5. The FDA UNII is 3ZO554A4Q8. Voxelotor has no defined stereocenters, according to current PubChem structural information.
Voxelotor was developed as a hemoglobin S polymerization inhibitor. It binds reversibly to hemoglobin and increases hemoglobin's oxygen affinity. This mechanism reduces the polymerization of deoxygenated hemoglobin S, a central molecular process involved in the sickling of red blood cells.
By modifying hemoglobin oxygen affinity, voxelotor was developed to address hemolysis and anemia associated with sickle cell disease. FDA's original approval was based on improvement in hemoglobin response and other hematologic parameters.
Voxelotor is a crystalline solid with a reported Form II polymorph. The drug substance is non-hygroscopic and has limited aqueous solubility. FDA reports that voxelotor is insoluble in water, with an approximate water solubility of 0.03 mg/mL. It is highly soluble in organic solvents including acetone and toluene.
Current chemical databases report an experimental melting-point value around 80–82°C, although this should be treated as a literature/reference physical property rather than a validated pharmaceutical release specification.
Voxelotor is a chemically synthesized small-molecule API. Manufacturing requires control of starting materials, intermediates, reaction conditions, purification and crystallization to consistently obtain the required crystalline drug substance.
The physical form is an important characteristic because voxelotor is reported in a defined crystalline Form II. Appropriate solid-state characterization can therefore be used during API development and manufacturing to confirm the required physical form.
Voxelotor API can be characterized using chromatographic and spectroscopic techniques. HPLC can be used for assay and related-substance testing, while infrared spectroscopy and other analytical techniques can support identity confirmation.
Additional analytical controls can include residual solvents, water content, elemental impurities, particle-size distribution and solid-state characterization. The applicable release criteria should be established according to the validated API specification.
Voxelotor was developed for the treatment of sickle cell disease. FDA initially granted accelerated approval in 2019 for adults and pediatric patients 12 years and older, followed by an accelerated approval in 2021 for patients 4 to 11 years of age.
However, the regulatory status must be clearly distinguished from historical approval. In September 2024, FDA announced that Oxbryta was being voluntarily withdrawn from the market because postmarketing data indicated increased vaso-occlusive crises and more deaths in voxelotor-treated groups compared with placebo in certain studies.
Important quality attributes for Voxelotor API include chemical identity, assay, related substances, crystalline form, residual solvents, water content, particle size and elemental impurities.
Because the drug substance is a crystalline small molecule, control of polymorphic form can be important for maintaining consistent pharmaceutical material characteristics. Analytical procedures should be appropriately validated for their intended use.
Voxelotor API can be considered as a specialized pharmaceutical research and development material for organizations working with hemoglobin-targeted compounds, analytical development and pharmaceutical manufacturing research.
Swapnroop Drugs & Pharmaceuticals provides pharmaceutical API solutions for research, development and manufacturing requirements. Voxelotor can be evaluated according to the customer's required technical specification, analytical requirements and applicable regulatory framework.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 1.0% |
| Residue on Ignition | NMT 0.20% |
| Heavy Metals | NMT 20 ppm |
| Individual Impurity | NMT 0.50% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 1.0% |
| Melting Point | 80–82°C |