Chemical Identity and Properties

3-Bromo-4-chloro-1H-pyrazolo[3,4-d]pyrimidine (Aladdin SKU: B178143) is a bicyclic heterocyclic compound comprising a fused pyrazole and pyrimidine ring system. The molecule carries two distinct halogen substituents: a bromine atom at position 3 and a chlorine atom at position 4. This pattern of halogenation endows the compound with orthogonal reactivity—the C3-bromo is well suited to palladium-catalysed cross-coupling reactions (e.g., Suzuki–Miyaura, Negishi), while the C4-chloro undergoes facile nucleophilic aromatic substitution (SNAr) with primary and secondary amines, thiolates, and alkoxides under mild conditions.

The pyrazolo[3,4-d]pyrimidine core is isosteric with purine and is therefore of significant interest as a pharmacophore in the design of adenosine receptor ligands, cyclin-dependent kinase (CDK) inhibitors, and other kinase-targeting therapeutics. Researchers should verify the exact CAS number, molecular weight, melting point, and purity against the lot-specific Certificate of Analysis (CoA) provided by Aladdin Scientific.

Safety and Handling Requirements

Personal Protective Equipment (PPE): Always wear nitrile gloves, a laboratory coat, and safety glasses when handling this compound. Work in a well-ventilated fume hood to minimise inhalation of dust or vapours.

Hazard Awareness: As a halogenated heterocycle, this compound should be treated as potentially irritating to skin, eyes, and the respiratory tract until full toxicological data are confirmed. Consult the Safety Data Sheet (SDS) provided by Aladdin Scientific before use. Avoid contact with strong bases or reducing agents that could cause uncontrolled dehalogenation.

Waste Disposal: Dispose of all waste, including contaminated gloves, vials, and solvent rinses, in accordance with your institution's chemical waste regulations. Do not pour halogenated organic waste into standard aqueous drains.

First Aid: In case of skin contact, wash thoroughly with soap and water for at least 15 minutes. In case of eye contact, irrigate with copious water and seek medical attention. If inhaled, move to fresh air immediately.

Solubility, Preparation, and Storage

Recommended Solvents: 3-Bromo-4-chloro-1H-pyrazolo[3,4-d]pyrimidine is generally soluble in polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF). Solubility in aqueous media is limited; DMSO stock solutions are typically prepared at 10–50 mM for biological assays. Verify solubility empirically under your specific experimental conditions.

Stock Solution Preparation:

1. Equilibrate the sealed vial to room temperature before opening to prevent moisture condensation on the solid.
2. Weigh the required quantity under inert atmosphere or in a dry glove bag if handling small quantities to minimise moisture exposure.
3. Dissolve in the minimum volume of the chosen solvent (e.g., DMSO) and vortex or sonicate briefly to achieve complete dissolution.
4. Aliquot into single-use volumes to avoid repeated freeze–thaw cycles.

Storage Conditions: Store at 2–8 °C in a tightly sealed container under an inert atmosphere (nitrogen or argon), protected from light and moisture. Check the label and CoA for any lot-specific storage deviations. When stored correctly, the compound is expected to be stable for the period stated on the certificate; verify expiry on CoA.

Synthetic Applications and Reaction Protocols

The orthogonal reactivity of the two halogen atoms makes this compound a particularly powerful two-directional building block in heterocyclic synthesis.

1. Nucleophilic Aromatic Substitution (SNAr) at C4-Cl:
The C4-chloro is highly activated towards SNAr owing to the electron-withdrawing nature of the flanking ring nitrogens. Reaction with primary or secondary amines typically proceeds in polar solvents (e.g., isopropanol, DMF, or THF) at 0 °C to 80 °C, often without the need for a metal catalyst. A mild base (e.g., triethylamine or DIPEA, 1.5–2.0 equivalents) is commonly employed to neutralise the HCl generated.

General SNAr procedure:

1. Charge a round-bottom flask with 3-Bromo-4-chloro-1H-pyrazolo[3,4-d]pyrimidine (1.0 equiv), the desired amine (1.0–1.2 equiv), and a base (1.5 equiv) in DMF or isopropanol (0.1–0.5 M).
2. Stir at 50–80 °C for 2–12 h, monitoring by TLC or LC-MS.
3. Cool to room temperature, dilute with ethyl acetate, wash with water and brine, dry over MgSO4, and concentrate.
4. Purify by column chromatography or recrystallisation.

2. Palladium-Catalysed Cross-Coupling at C3-Br:
After selective SNAr functionalisation of C4, the remaining C3-bromo can be engaged in Suzuki–Miyaura coupling with aryl- or heteroarylboronic acids, Negishi coupling with organozinc reagents, or Buchwald–Hartwig amination. Standard Pd(0)/Pd(II) catalyst systems (e.g., Pd(PPh3)4, Pd(dppf)Cl2, or Pd2(dba)3 with XPhos) and aqueous carbonate or phosphate bases in toluene/ethanol or dioxane/water solvent mixtures are appropriate starting points. Reaction temperatures of 80–100 °C are typical.

3. N1-Alkylation:
The NH tautomer of the pyrazole can be selectively alkylated under basic conditions (K2CO3, Cs2CO3) using alkyl halides in DMF, providing N1-substituted analogues useful for SAR exploration. Monitor regioselectivity carefully, as N2-alkylation can compete.

Quality Control and Troubleshooting

Purity Verification: Upon receipt, verify compound identity and purity using ¹H NMR, ¹³C NMR, and LC-MS or HPLC. The CoA supplied with each lot from Aladdin Scientific provides reference data. Discoloration or caking of the solid may indicate moisture uptake or degradation; in such cases, contact Aladdin Scientific for a replacement.

Common Issues and Remedies:

• Incomplete SNAr reaction: Increase temperature incrementally (up to 100 °C in DMF) or switch to a more nucleophilic amine. Ensure the amine is anhydrous.
• Low cross-coupling yield: Check catalyst loading and ligand-to-palladium ratio. Degas all solvents thoroughly with argon or nitrogen before use. Ensure the boronic acid or organometallic partner is not hydrolysed or oxidised.
• N-alkylation regioselectivity issues: Conduct the reaction at lower temperature and use milder bases. Analyse regioisomers by NOE or X-ray crystallography if ambiguous.
• Decomposition in solution: Avoid prolonged storage in protic solvents. Prepare fresh stock solutions where possible and store aliquots at −20 °C under argon.

Analytical Characterisation Checklist: LC-MS (purity and molecular ion), ¹H NMR (structural confirmation), melting point (comparison with CoA), and elemental analysis or HRMS (for publication-grade characterisation).