Zanubrutinib is a selective, orally active Bruton’s tyrosine kinase (BTK) inhibitor used as a pharmaceutical active ingredient in targeted oncology therapies. It is also known by its development code BGB-3111 and is marketed under the brand name Brukinsa. Zanubrutinib belongs to the second-generation BTK inhibitor class and is designed to selectively inhibit BTK, an important signaling protein involved in the development and survival of B cells.
Zanubrutinib is a synthetic small-molecule pharmaceutical API with the molecular formula C27H29N5O3 and molecular weight of approximately 471.5 g/mol. Its correct CAS Number is 1691249-45-2, and its FDA UNII is AG9MHG098Z. The API is the S-enantiomer of zanubrutinib and contains a defined chiral center.
The chemical structure contains a pyrazolo[1,5-a]pyrimidine core, a phenoxyphenyl group, a piperidine ring and an acryloyl functionality. Its structural design provides strong and selective interaction with the BTK enzyme.
The chemical name of Zanubrutinib is (7S)-2-(4-phenoxyphenyl)-7-(1-prop-2-enoylpiperidin-4-yl)-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-3-carboxamide. PubChem reports an exact mass of approximately 471.2270 Da, with a calculated topological polar surface area of approximately 102 Ų.
Zanubrutinib is a relatively lipophilic compound with a calculated XLogP3-AA value of approximately 3.5. It has two hydrogen-bond donors and five hydrogen-bond acceptors.
Zanubrutinib works by inhibiting Bruton’s tyrosine kinase, an enzyme that plays a central role in B-cell receptor signaling.
BTK participates in signaling pathways that regulate B-cell development, activation, proliferation and survival. By binding to and inhibiting BTK, Zanubrutinib suppresses signaling pathways that contribute to malignant B-cell proliferation and survival.
Zanubrutinib is designed to form a covalent interaction with BTK, producing sustained inhibition of the target enzyme. This pharmacological mechanism makes it particularly relevant to B-cell malignancies.
Zanubrutinib was developed as a highly selective BTK inhibitor with the objective of minimizing activity against other kinases. Its selectivity profile is an important characteristic distinguishing it from earlier BTK inhibitors.
The API is therefore relevant to pharmaceutical development involving targeted therapies for B-cell malignancies and other hematological oncology applications.
FDA describes Zanubrutinib drug substance as a white to off-white, slightly hygroscopic solid. It is manufactured as a single polymorphic form, identified in the regulatory assessment as Form A. FDA also characterizes it as a BCS Class II compound with poor aqueous solubility and high permeability.
Published pharmaceutical-development information reports an endothermic melting event with an initial temperature around 139°C, a peak around 144°C, and an API melting point around 145°C. Another analytical reference source reports a melting range of 146.8–148.8°C. These values can vary with analytical method, solid form and sample preparation.
Zanubrutinib has low aqueous solubility and is classified as a BCS Class II compound. FDA describes the drug substance as practically insoluble in water while being freely soluble in organic solvents including methanol, acetone, DMSO and THF.
The low aqueous solubility and high permeability of Zanubrutinib are important pharmaceutical-development characteristics because they influence dissolution, formulation performance and oral bioavailability.
Zanubrutinib is manufactured as a chemically synthesized small-molecule API. The manufacturing process involves controlled chemical synthesis, purification and isolation of the desired S-enantiomer.
FDA's quality assessment describes the drug substance as a single chiral molecule and confirms that manufacturing controls include controls for regulatory starting materials, critical process parameters, in-process controls and impurity fate and purge.
Control of stereochemical purity is particularly important because Zanubrutinib is supplied as a defined single enantiomer rather than a racemic mixture.
Quality control of Zanubrutinib includes identity, assay, related substances, stereochemical purity, residual solvents, water/moisture, elemental impurities and physical characteristics.
FDA states that the analytical methods supporting the drug-substance specification were evaluated for parameters including specificity, linearity, range, precision, accuracy, ruggedness, robustness and solution stability.
Current analytical reference material is reported at >99.0% HPLC purity, while another current commercial API listing reports 99.0% HPLC assay. These values demonstrate the availability of high-purity Zanubrutinib material but should not be represented as an official USP/BP release limit.
Related substances are an important part of Zanubrutinib API quality control. The FDA assessment confirms that impurity controls and impurity fate/purge studies were included in the regulatory CMC package.
Because Zanubrutinib contains a reactive acryloyl group and multiple synthetic intermediates can arise during manufacture, chromatographic control of process-related and degradation-related impurities is important.
Public regulatory documents do not disclose all numerical acceptance limits for individual Zanubrutinib impurities. Therefore, specific impurity limits should be taken from the applicable validated API specification or DMF rather than invented for a public product page.
Zanubrutinib is a single-enantiomer API. The correct pharmaceutical substance is the S-isomer with CAS 1691249-45-2. The corresponding R-isomer is separately identified with CAS 1691249-44-1, while the racemic material has CAS 1633350-06-7.
For pharmaceutical manufacturing, stereochemical identity and enantiomeric purity are therefore important quality attributes.
Zanubrutinib is used in targeted treatment of several B-cell malignancies. Current U.S. labeling identifies indications including mantle cell lymphoma, Waldenström's macroglobulinemia, marginal zone lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma and certain follicular lymphoma settings.
FDA records show that Zanubrutinib continues to have active U.S. regulatory status, with the most recent U.S. labeling record dated June 15, 2026.
Zanubrutinib is relevant to pharmaceutical formulation development, analytical research, generic-development programs and commercial API sourcing. Its BCS Class II characteristics make dissolution and formulation performance particularly important during dosage-form development.
The API is generally handled as a crystalline solid and requires appropriate control of particle characteristics, moisture exposure, polymorphic form and chemical purity.
Zanubrutinib is described as slightly hygroscopic. Appropriate protection from moisture, excessive heat and strong light is therefore recommended during storage and handling.
Research/reference sources recommend dry storage and, depending on the material and supplier, controlled refrigerated or frozen conditions. Commercial pharmaceutical API storage should ultimately follow the validated stability data and manufacturer's approved specification.
Zanubrutinib is an oncology-focused small-molecule API with established regulatory use and well-defined chemical identity. Pharmaceutical-grade material requires appropriate controls for assay, related substances, stereochemical purity, residual solvents, water content and physical characteristics.
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| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | NLT 99.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.1% |
| Heavy Metals | NMT 20 ppm |
| Individual Impurity | NMT 0.10% |
| Total Impurities | NMT 1.0% |
| Melting Point | 145–149°C |