Handling & Use Guide: (S)-Boc-3-Bromophenyl-β-Alanine

(S)-3-(3-Bromophenyl)-3-((tert-butoxycarbonyl)amino)propanoic acid is a Boc-protected, enantiopure β-amino acid building block featuring a meta-bromine handle on the phenyl ring, making it a versatile intermediate for asymmetric peptide assembly, fragment coupling, and further palladium-catalyzed cross-coupling reactions in pharmaceutical and medicinal chemistry research.

Chemical Name

(S)-3-(3-Bromophenyl)-3-((tert-butoxycarbonyl)amino)propanoic acid

SKU

A710042

Compound Class

Boc-protected chiral β-amino acid

Key Functional Groups

Boc-protected amine, free carboxylic acid, aryl bromide

Sterochemistry

(S)-configuration at the β-carbon

Primary Application

Peptide synthesis building block; pharmaceutical intermediate; cross-coupling substrate

Recommended Storage

Cool, dry, well-ventilated area; protect from moisture and light; store sealed

Chemical Identity and Structure

(S)-3-(3-Bromophenyl)-3-((tert-butoxycarbonyl)amino)propanoic acid (Aladdin SKU A710042) is an enantiopure β³-amino acid derivative in which the amino group is protected as a tert-butoxycarbonyl (Boc) carbamate. The compound carries three synthetically useful features in a single scaffold: (1) a free carboxylic acid at the β-position available for coupling or activation; (2) a Boc-protected primary amine at the α-carbon that can be selectively deprotected under mild acidic conditions; and (3) a meta-bromo substituent on the phenyl ring that serves as a handle for palladium- or copper-catalyzed cross-coupling reactions such as Suzuki–Miyaura, Buchwald–Hartwig, or Sonogashira couplings.

The (S)-stereochemistry at the β-carbon is critical for applications in asymmetric synthesis and the preparation of biologically active peptide mimetics. Researchers should verify the enantiomeric excess (ee) via chiral HPLC or optical rotation measurement upon receipt and record the result in their laboratory notebook for traceability.

Storage and Stability Guidelines

Storage conditions: Store the compound in a tightly sealed container in a cool (2–8 °C is recommended for long-term stock solutions; room temperature is acceptable for sealed solid material in the short term), dry, and well-ventilated area, protected from moisture and direct light. Moisture can promote hydrolysis of the Boc carbamate and the carboxylic acid functionality over extended periods.

Stability considerations: The Boc group is stable under neutral and basic aqueous conditions but is labile to strong acids (e.g., trifluoroacetic acid, hydrochloric acid in dioxane) and prolonged exposure to high temperatures. The aryl bromide is stable under standard storage conditions but may undergo slow oxidation or degradation if the compound is stored improperly. Avoid exposure to strong bases, which may epimerize the β-stereocentre or hydrolyse the Boc group.

Container management: Upon opening, purge the container with inert gas (nitrogen or argon), reseal immediately, and return to appropriate storage. Prepare stock solutions in dry organic solvents (e.g., anhydrous DMF, DMSO, or DCM) and store aliquots at −20 °C to maximise shelf life.

Laboratory Handling and Safety Precautions

Personal protective equipment (PPE): Always wear appropriate PPE when handling this compound, including nitrile gloves, safety glasses or goggles, and a laboratory coat. Work in a well-ventilated fume hood, especially when weighing powder or preparing concentrated solutions, to minimise inhalation of fine particulates.

Skin and eye contact: Avoid direct contact with skin and eyes. In the event of skin contact, wash the affected area thoroughly with soap and water. In the event of eye contact, irrigate immediately with copious amounts of water for at least 15 minutes and seek medical attention.

Waste disposal: Dispose of waste material in accordance with local, regional, and national regulations for organohalide-containing chemical waste. Do not pour solutions containing aryl bromides down the drain. Collect in appropriately labelled solvent-waste containers and arrange for licensed chemical waste disposal.

Spill management: For small solid spills, carefully collect the material with a damp cloth or absorbent paper and transfer to a labelled waste container. Avoid generating dust. For solution spills, absorb with an inert material (e.g., vermiculite or dry sand), collect, and dispose as chemical waste.

Synthetic Applications and Reaction Protocols

As a peptide coupling partner: The free carboxylic acid can be activated using standard peptide coupling reagents such as HATU, HBTU, DIC/HOBt, or EDC/HOBt in the presence of a non-nucleophilic base (e.g., DIPEA or NMM) in anhydrous DMF or DCM. The Boc group is orthogonal to Fmoc-based SPPS side-chain protection strategies, enabling selective deprotection sequences. Typical coupling reactions are performed at 0 °C to room temperature with reaction times of 2–16 hours depending on the amine coupling partner.

Boc deprotection: Remove the Boc protecting group by treatment with 20–50% trifluoroacetic acid (TFA) in dichloromethane (DCM) at room temperature for 30–60 minutes, or with 4 M HCl in 1,4-dioxane. After deprotection, remove volatiles under reduced pressure and neutralise the resulting TFA or HCl salt with base before the next synthetic step. Monitor reaction progress by TLC or LC-MS.

Cross-coupling reactions via the aryl bromide: The meta-aryl bromide is an excellent substrate for Pd(0)- or Pd(II)-catalysed cross-coupling. Suzuki–Miyaura couplings with arylboronic acids, Buchwald–Hartwig aminations, and carbonylation reactions can be performed to introduce structural diversity. Protect the carboxylic acid as a methyl or ethyl ester prior to cross-coupling if required by the catalyst system. Standard Suzuki conditions (e.g., Pd(PPh₃)₄ or Pd(dppf)Cl₂, K₂CO₃, DMF/water, 80–100 °C) are applicable; optimise base, solvent, and temperature to preserve the Boc group and stereocentre.

Important note: Always perform a small-scale test reaction before committing large quantities of material to confirm reaction conditions are compatible with the Boc group and the (S)-stereocentre stability under the chosen conditions.

Quality Control and Troubleshooting

Purity verification: Upon receipt, verify compound purity by HPLC (reverse-phase C18 column, UV detection at 210 nm or 254 nm) and confirm identity by ¹H NMR and high-resolution mass spectrometry (HRMS). Check the certificate of analysis (CoA) provided by Aladdin Scientific for reported purity, optical rotation, and any spectral data.

Enantiomeric integrity: Confirm the (S)-configuration and enantiomeric excess (ee) by chiral HPLC or by comparing the optical rotation [α]D with literature values. Any significant deviation may indicate partial racemisation during shipping or storage.

Common issues and solutions:

• Low coupling yields: May result from incomplete activation of the carboxylic acid. Ensure reagents are dry and anhydrous, increase equivalents of coupling reagent, or switch to a more reactive activating agent (e.g., HATU instead of HBTU).
• Racemisation during coupling: Use milder bases (e.g., 2,6-lutidine or collidine instead of DIPEA at elevated temperature), lower the reaction temperature, or add racemisation suppressants such as HOAt.
• Incomplete Boc deprotection: Extend TFA treatment time or increase TFA concentration. Ensure DCM is dry. Alternatively, switch to HCl/dioxane (4 M) for more reliable deprotection.
• Poor cross-coupling conversion: Check catalyst loading and ligand. Degas solvents thoroughly to remove oxygen, which can poison palladium catalysts. Consider protecting the carboxylic acid before the cross-coupling step.

Frequently asked questions

What solvents are recommended for dissolving (S)-3-(3-Bromophenyl)-3-((tert-butoxycarbonyl)amino)propanoic acid?

This compound is generally soluble in polar aprotic solvents such as DMF and DMSO, as well as in chlorinated solvents such as DCM and CHCl₃. It has limited solubility in non-polar solvents such as hexane or diethyl ether. For stock solutions intended for long-term storage, anhydrous DMF or DMSO is recommended; aliquots should be stored at −20 °C under inert atmosphere to prevent moisture ingress and Boc hydrolysis.

How should the Boc protecting group be removed without compromising the (S)-stereocentre?

Boc deprotection is typically performed with 20–50% TFA in DCM or 4 M HCl in 1,4-dioxane at room temperature for 30–60 minutes. These mild acidic conditions cleave the Boc group via a carbocation mechanism without epimerising the β-stereocentre. Avoid strong acids at elevated temperatures, prolonged reaction times, or strongly basic conditions, as these can promote racemisation. Confirm enantiomeric integrity of the product by chiral HPLC after deprotection.

Can the aryl bromide of this compound be used directly in Suzuki–Miyaura cross-coupling reactions?

Yes, the meta-aryl bromide is well-suited for Suzuki–Miyaura and other palladium-catalysed cross-coupling reactions. Standard conditions using Pd(PPh₃)₄ or Pd(dppf)Cl₂ as catalyst, K₂CO₃ as base, and DMF/water as solvent at 80–100 °C are typically effective. It is advisable to protect the carboxylic acid as an ester and to optimise conditions to ensure the Boc group and stereocentre remain intact, since prolonged high-temperature exposure may affect them. Always conduct a small-scale optimisation experiment first.

What analytical methods are recommended to confirm the identity and purity of this compound?

Identity should be confirmed by ¹H NMR (characteristic peaks for the Boc tert-butyl group at ~1.4 ppm, aromatic protons, and NH), ¹³C NMR, and HRMS. Purity is best assessed by reverse-phase HPLC with UV detection. Enantiomeric purity should be verified by chiral HPLC or optical rotation measurement. The CoA provided with the product from Aladdin Scientific should be consulted as a reference.

References

1. Cardillo, G.; Orena, M. Asymmetric synthesis of β-amino acids. Tetrahedron 1990, 46, 2263–2282. [General reference on β-amino acid synthesis — specific applicability to this compound needs verification]
2. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. [General reference for Suzuki–Miyaura coupling applicable to aryl bromide substrates] doi:10.1021/cr00039a007
3. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.; Wiley-Interscience: New York, 2007. [Standard reference for Boc protection and deprotection conditions]

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