Overview and Chemical Properties

cis-3-Aminocyclobutanecarboxylic acid hydrochloride (Aladdin SKU: C194854) is a conformationally restricted β-amino acid in which an amino group and a carboxylic acid group are positioned in a cis relationship across a four-membered carbocyclic ring. The hydrochloride salt form enhances the compound's stability during long-term storage and improves handling characteristics compared with the free base.

The cyclobutane ring introduces geometric rigidity, fixing the relative orientation of the two functional groups. This constraint is highly valuable in drug discovery, where control over three-dimensional molecular geometry can improve target selectivity and metabolic stability relative to flexible acyclic analogues. As a β-amino acid building block, it does not bear an α-carbon between the amino and carboxyl groups in the conventional sense but instead incorporates both functionalities on the cyclobutane scaffold, enabling access to novel peptidomimetic architectures.

Materials and Safety Precautions

Required materials:

• cis-3-Aminocyclobutanecarboxylic acid hydrochloride (C194854)
• Appropriate solvent: ultrapure water, methanol, or dimethyl sulfoxide (DMSO) depending on downstream application
• Analytical balance (0.1 mg readability)
• Volumetric glassware or calibrated micropipettes
• Inert atmosphere supply (nitrogen or argon) if the reaction medium requires exclusion of moisture
• Personal protective equipment (PPE): laboratory coat, chemical-resistant gloves, safety goggles

Safety precautions:

• As a hydrochloride salt, the compound is mildly acidic in aqueous solution; avoid contact with eyes, skin, and mucous membranes.
• Handle in a well-ventilated area or fume hood.
• Consult the Safety Data Sheet (SDS) for complete hazard information before use.
• Dispose of waste in accordance with local chemical waste regulations.

Step-by-Step Protocol: Solution Preparation and Coupling Reaction

Step 1 – Equilibrate the compound to room temperature. Remove the vial of C194854 from cold storage (2–8 °C) and allow it to equilibrate to ambient temperature (approximately 20–25 °C) for 15–20 minutes before opening. This minimises condensation-induced degradation of the hygroscopic salt.

Step 2 – Weigh the compound. Tare an appropriate vessel on an analytical balance. Quickly transfer the desired mass of cis-3-Aminocyclobutanecarboxylic acid hydrochloride and reseal the stock vial under inert gas if possible. Record the exact mass.

Step 3 – Prepare the stock solution. For aqueous applications, dissolve the compound in ultrapure water to the desired concentration. Vortex or stir gently until fully dissolved. For organic synthesis, dissolve in anhydrous DMF, DMSO, or another compatible polar aprotic solvent. Filter through a 0.22 µm syringe filter if solution clarity is required.

Step 4 – Neutralise the hydrochloride (if required). When the free-base form of the amine is needed for coupling reactions, add an equivalent of a mild base such as triethylamine (Et₃N) or N,N-diisopropylethylamine (DIPEA) to the reaction mixture to liberate the free amine in situ. Ensure stoichiometric accuracy to avoid excess base.

Step 5 – Execute the coupling or synthetic step. Introduce standard coupling reagents (e.g., HATU, EDC/NHS, or DIC/HOBt) according to your validated synthetic protocol. The cis-constrained amine and carboxylic acid can both participate in amide bond formation; ensure correct protecting-group strategy to achieve selective functionalization.

Step 6 – Work-up and purification. After reaction completion (monitor by TLC or LC-MS), perform standard aqueous work-up or direct purification by reverse-phase HPLC or column chromatography as appropriate to your target molecule.

Applications in Medicinal and Synthetic Chemistry

cis-3-Aminocyclobutanecarboxylic acid hydrochloride is a versatile scaffold utilised across multiple research disciplines:

• Peptidomimetic design: The rigid cis geometry mimics turn structures found in bioactive peptides, enabling the design of metabolically stable peptide surrogates with defined conformational preferences.
• Drug discovery building blocks: The compound serves as an intermediate for the synthesis of kinase inhibitors, protease inhibitors, and GPCR modulators where a constrained amine or acid handle is required.
• Heterocyclic chemistry: The primary amine and carboxylic acid functions can be elaborated into lactams, oxazolines, or other ring-fused systems, providing rapid access to complex molecular architectures.
• Structure–activity relationship (SAR) studies: Comparison of cis versus trans diastereomers allows researchers to dissect the contribution of stereochemical orientation to biological activity.

Troubleshooting and Storage Recommendations

Common issues and resolutions:

• Poor solubility in organic solvents: The hydrochloride salt has limited solubility in non-polar or mildly polar organic solvents. Switch to DMSO or DMF, or neutralise with base prior to dissolution in organic media.
• Incomplete coupling reaction: Ensure the free-base amine is liberated by adequate base addition. Verify reagent stoichiometry and reaction time. Consider switching to a more activated coupling reagent.
• Degradation or discoloration of stored material: This typically indicates moisture ingress. Store rigorously sealed under inert gas at 2–8 °C. Discard and replace material that shows visible discoloration.

Storage and stability:

• Store at 2–8 °C in a tightly closed, moisture-proof container.
• Protect from light and heat.
• Prepare fresh solutions where possible; if stock solutions must be stored, aliquot into single-use volumes and freeze at −20 °C under inert atmosphere.
• Always re-equilibrate to room temperature before opening to avoid moisture condensation on the cold solid.