4-Borono-D-Phenylalanine: Properties, Uses & BNCT Role

4-Borono-D-phenylalanine is the D-enantiomer of the boronic acid-substituted phenylalanine derivative widely studied as a boron-10 carrier and mechanistic probe in boron neutron capture therapy (BNCT) research.

Chemical Name

4-Borono-D-phenylalanine

Enantiomer

D-configuration (R) at the alpha-carbon

Key Functional Groups

Boronic acid (–B(OH)₂), amino (–NH₂), carboxylic acid (–COOH)

Primary Research Application

Boron neutron capture therapy (BNCT) mechanistic studies and enantiomeric control experiments

Boron Isotope Relevance

Contains natural boron; ¹⁰B-enriched analogue used therapeutically

Relationship to L-BPA

D-enantiomer counterpart of L-BPA (L-boronophenylalanine), used as stereochemical control

Chemical Structure and Properties

4-Borono-D-phenylalanine (D-BPA) is a synthetic amino acid bearing a boronic acid group at the para position of the phenylalanine phenyl ring. Its molecular formula is C₉H₁₂BNO₄, with a molecular weight of approximately 225.01 g/mol. The compound possesses three ionizable functional groups: an alpha-amino group, an alpha-carboxylic acid group, and the arylboronic acid moiety, which can exist in equilibrium between the trigonal planar boronic acid form and the tetrahedral boronate anion depending on pH.

The D-configuration at the alpha-carbon distinguishes D-BPA from its clinically investigated counterpart, L-boronophenylalanine (L-BPA). This stereochemical difference has significant consequences for biological transport and receptor recognition. Boronic acids are known to form reversible covalent bonds with cis-diol-containing molecules such as sugars and certain biological substrates, a property relevant to the study of boron delivery in cellular systems.

Role in Boron Neutron Capture Therapy Research

Boron neutron capture therapy (BNCT) is a binary radiotherapy modality that relies on the nuclear reaction between boron-10 (¹⁰B) and thermal or epithermal neutrons to generate high-linear-energy-transfer (LET) particles—specifically an alpha particle (⁴He) and a lithium-7 (⁷Li) recoil nucleus—that deposit lethal energy within targeted cells. Selective accumulation of ¹⁰B in tumor cells is therefore critical to therapeutic efficacy.

L-BPA is the primary phenylalanine-based boron carrier investigated in BNCT clinical research, exploiting the preferential uptake of phenylalanine analogues by tumor cells via amino acid transport systems, notably the L-type amino acid transporter (LAT1). D-BPA serves as an important stereospecific control reagent in laboratory studies: because biological amino acid transporters are predominantly stereoselective for L-amino acids, D-BPA exhibits substantially reduced cellular uptake compared to L-BPA, allowing researchers to dissect transporter-mediated versus passive or non-specific uptake of BPA in cell culture and animal models.

Laboratory Applications and Experimental Design

In mechanistic cell biology and radiobiology laboratories, D-BPA is primarily employed as a negative or stereochemical control paired with L-BPA uptake assays. By comparing intracellular boron concentrations or downstream effects of L-BPA versus D-BPA treatment under identical conditions, investigators can confirm that observed transport phenomena are stereospecific and transporter-dependent rather than attributable to passive diffusion or non-specific membrane interactions.

D-BPA is also used in competitive inhibition studies to probe the substrate specificity and kinetics of amino acid transporters, and in studies examining the physicochemical behavior of boronic acids at physiological pH. Its well-defined stereochemistry makes it suitable for validating analytical methods—such as inductively coupled plasma mass spectrometry (ICP-MS) or prompt gamma activation analysis (PGAA)—used to quantify boron content in biological samples. Researchers should note that working solutions of boronic acids may require careful pH adjustment to ensure solubility and stability.

Handling, Storage, and Safety Considerations

4-Borono-D-phenylalanine should be handled in accordance with standard laboratory safety practices for synthetic amino acid derivatives. The compound should be stored in a cool, dry environment away from moisture and strong oxidizing agents. Boronic acids can slowly oxidize under ambient conditions; therefore, containers should be tightly sealed and, where possible, stored under inert atmosphere or with desiccant to preserve purity.

Researchers should consult the product-specific Safety Data Sheet (SDS) provided by Aladdin Scientific before use. Personal protective equipment including laboratory coat, gloves, and safety eyewear is recommended during weighing and solution preparation. Waste disposal should comply with local institutional and regulatory requirements for chemical waste. As with all fine research chemicals, documentation of lot number and purity certificate data is recommended for experimental reproducibility and regulatory compliance.

Frequently asked questions

What is the difference between D-BPA and L-BPA in BNCT research?

L-BPA (L-boronophenylalanine) is the biologically active enantiomer preferentially transported into tumor cells via stereoselective amino acid transporters such as LAT1, and is the form investigated in clinical BNCT protocols. D-BPA is the enantiomeric counterpart that exhibits substantially reduced transporter-mediated uptake due to the stereoselectivity of these carriers, making it an ideal negative control to confirm that L-BPA uptake is transporter-dependent and stereospecific.

How should 4-Borono-D-phenylalanine be dissolved for cell-based assays?

4-Borono-D-phenylalanine is typically dissolved in aqueous buffers or cell culture media at physiological or near-physiological pH. Solubility may be limited at neutral pH; gentle warming or addition of dilute base (e.g., sodium hydroxide solution) can improve dissolution. Researchers should verify pH after dissolution and filter-sterilize solutions before cell culture use. Specific solubility data should be confirmed from the product certificate of analysis.

Can D-BPA be used to validate boron quantification methods?

Yes, D-BPA with known purity and defined molecular weight serves as a convenient boron-containing reference standard for method validation of analytical techniques such as ICP-MS or PGAA, which are commonly used to measure boron concentrations in biological and tissue samples. Its well-characterized structure ensures reliable preparation of calibration standards when used alongside a certificate of analysis.

What storage conditions are recommended for 4-Borono-D-phenylalanine?

The compound should be stored in a tightly sealed container in a cool, dry location away from moisture, light, and strong oxidizing agents. Storage with a desiccant and, where practical, under inert gas is advisable to minimize oxidation of the boronic acid group. Always refer to the Aladdin Scientific product label and SDS for lot-specific storage recommendations.

References

1. Hawthorne, M. F. The Role of Chemistry in the Development of Boron Neutron Capture Therapy of Cancer. Angewandte Chemie International Edition, 1993.
2. Barth, R. F.; Coderre, J. A.; Vicente, M. G. H.; Blue, T. E. Boron Neutron Capture Therapy of Cancer: Current Status and Future Prospects. Clinical Cancer Research, 2005.
3. Nakamura, H.; Kawamura, M.; Nakai, K.; Yamamoto, T.; Matsumura, A. Tumor Selective Accumulation of Boron by L-BPA and Its Enantiomeric Control Studies Using D-BPA. (General reference; specific citation details require verification.)

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