(S)-Boc-O-Ethyl-Serine: Handling & Usage Protocol

(S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid is a Boc-protected, O-ethylated non-natural serine derivative widely used as a chiral building block in solid-phase and solution-phase peptide synthesis.

Chemical Name

(S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid

SKU

A728215

Compound Class

Boc-protected non-natural amino acid (O-alkyl serine derivative)

Stereochemistry

S-configuration (analogous to L-serine backbone)

Primary Application

Chiral building block for peptide synthesis and medicinal chemistry

Key Functional Groups

Boc-protected amine, carboxylic acid, O-ethyl ether

Compound Overview and Significance

(S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid (Aladdin SKU: A728215) is a non-natural amino acid building block derived from L-serine, in which the hydroxyl side chain has been alkylated with an ethyl group and the α-amino group is protected with a tert-butoxycarbonyl (Boc) group. The free carboxylic acid moiety allows direct coupling to amines or solid supports without additional activation of that terminus.

The Boc protecting group provides robust stability under basic and neutral conditions while remaining selectively removable under mild acidic conditions (e.g., trifluoroacetic acid in DCM or 4 M HCl in dioxane). The O-ethyl modification of the serine side chain imparts resistance to enzymatic degradation and modulates the physicochemical properties of peptides incorporating this residue, making it valuable in the design of protease-resistant peptide analogs and peptidomimetics.

Storage and Safety Handling

Storage: Store the compound in a tightly sealed container under an inert atmosphere (nitrogen or argon) at 2–8 °C or as specified on the product label. Protect from moisture, light, and heat. For long-term storage, consider keeping the material at −20 °C. Always allow the container to equilibrate to room temperature before opening to prevent moisture condensation on the solid.

Personal Protective Equipment (PPE): Wear appropriate PPE including nitrile gloves, a laboratory coat, and safety goggles when handling this compound. Work in a well-ventilated fume hood. Consult the Safety Data Sheet (SDS) prior to use for complete hazard information.

Stability note: The Boc group is sensitive to strong acids, elevated temperatures, and prolonged exposure to protic solvents. Avoid exposure to trifluoroacetic acid (TFA), HCl solutions, or other strong acid media unless intentional Boc deprotection is desired.

Step-by-Step Protocol: Boc Deprotection and Peptide Coupling

The following general protocol describes how to incorporate (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid into a peptide chain using standard solution-phase coupling chemistry. Adapt reaction scales and conditions to your specific synthetic targets.

Materials Required

• (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid (A728215)
• Coupling reagents: e.g., HATU or HBTU (1.0–1.2 equiv), DIPEA or TEA (2.0–3.0 equiv)
• Amine coupling partner or resin-bound amine (for SPPS)
• Anhydrous DMF or DCM as solvent
• TFA/DCM (1:1 v/v) for Boc deprotection
• Inert atmosphere (N₂ or Ar) capability

Procedure

1. Preparation: Dry all glassware and solvents thoroughly. Weigh the Boc-amino acid under an inert atmosphere or in a dry glove bag to minimize moisture exposure.
2. Dissolution: Dissolve the Boc-amino acid (1.0 equiv) in anhydrous DMF or DCM at a concentration of 0.1–0.5 M. Stir gently until complete dissolution is achieved.
3. Activation: Add the coupling reagent (e.g., HATU, 1.1 equiv) followed by DIPEA (2.5 equiv) to the Boc-amino acid solution. Allow pre-activation for 2–5 minutes at room temperature with stirring.
4. Coupling: Add the amine coupling partner (1.0 equiv) to the activated ester solution. Stir at room temperature for 1–4 hours. Monitor reaction progress by TLC or HPLC.
5. Workup: Upon completion, dilute the reaction mixture with ethyl acetate and wash sequentially with saturated NH₄Cl, saturated NaHCO₃, and brine. Dry the organic layer over anhydrous Na₂SO₄, filter, and concentrate under reduced pressure.
6. Boc Deprotection (if required): Dissolve the Boc-protected product in DCM. Add TFA (50% v/v) and stir at room temperature for 30–60 minutes. Monitor by TLC/LCMS. Remove TFA and DCM under reduced pressure; co-evaporate with toluene (×2) to remove residual TFA. The free amine salt may be used directly or neutralized before further steps.
7. Purification: Purify the product by column chromatography (silica gel, suitable eluent system) or preparative HPLC as appropriate.

Quality Control and Analytical Characterization

After synthesis or prior to use, confirm the identity and purity of (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid using the following analytical techniques:

• TLC: Use silica gel plates with a suitable solvent system (e.g., hexane/ethyl acetate or DCM/MeOH). Visualize with UV (254 nm) and/or ninhydrin staining (after Boc removal).
• HPLC: Reversed-phase C18 column; monitor at 210–220 nm (amide/carboxylate absorption). Target purity ≥95% for synthetic applications.
• NMR: ¹H and ¹³C NMR in CDCl₃ or DMSO-d₆ to confirm structural integrity, stereochemistry, and absence of racemization. The Boc group typically appears as a singlet near δ 1.4 ppm (¹H NMR, 9H).
• Mass Spectrometry: ESI-MS or APCI-MS to confirm molecular ion [M+H]⁺ or [M+Na]⁺. Verify the expected molecular weight consistent with the molecular formula.
• Optical Rotation: Measure specific optical rotation to confirm S-configuration retention; compare against literature or certificate of analysis values.

Troubleshooting and Common Issues

The following table addresses common challenges encountered when working with (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid:

• Low coupling yield: Ensure coupling reagents are fresh and anhydrous. Increase equivalents of coupling reagent (up to 1.5 equiv) or extend reaction time. Check for moisture contamination in solvents.
• Racemization during coupling: Use milder base (DIPEA preferred over NaH or DBU). Employ HOAt or HOBt as additive to suppress racemization. Keep reaction temperatures at 0 °C to room temperature.
• Incomplete Boc deprotection: Increase TFA concentration or extend deprotection time. Ensure sufficient scavengers (e.g., triisopropylsilane, water) are present if needed for acid-sensitive protecting groups elsewhere in the molecule.
• Compound aggregation or poor solubility: Try alternative solvents such as DMSO, DMF, or NMP. Gentle warming (30–40 °C) may assist dissolution; avoid temperatures that could cause decomposition.
• Unexpected side products: Monitor reactions closely by TLC/HPLC. Reduce activation time if over-activation or OBt-ester formation is suspected. Ensure amine component is free of salts before coupling.

Frequently asked questions

What solvent is recommended for dissolving (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid?

Anhydrous DMF or DCM are the most commonly used solvents for this Boc-protected amino acid in coupling reactions. For analytical purposes, DMSO-d₆ or CDCl₃ are suitable NMR solvents. Avoid protic solvents such as water or alcohols in reactions where the Boc group or active esters must be preserved.

How should the Boc group be removed from this compound?

The Boc group is typically removed using trifluoroacetic acid (TFA) in DCM (20–50% v/v) at room temperature for 30–60 minutes, or using 4 M HCl in dioxane. After deprotection, remove acid under reduced pressure and co-evaporate with toluene to eliminate residual TFA. The resulting free amine is typically obtained as its TFA or HCl salt.

How does the O-ethyl modification on the serine side chain affect reactivity?

The O-ethyl ether on the side chain replaces the free hydroxyl group of serine, eliminating the risk of O-acylation side reactions during peptide coupling. This modification simplifies the synthetic strategy by removing the need for side-chain hydroxyl protection, while also conferring increased metabolic stability to the resultant peptide or peptidomimetic product.

Is this compound suitable for solid-phase peptide synthesis (SPPS)?

Yes, (S)-2-((tert-Butoxycarbonyl)amino)-3-ethoxypropanoic acid is compatible with Boc-based SPPS strategies. The free carboxylic acid can be activated and coupled to resin-bound amines using standard coupling reagents (e.g., HATU, HBTU). Because the side chain is already O-ethylated and requires no orthogonal protection, it integrates efficiently into automated or manual SPPS workflows.

What are the recommended storage conditions and shelf life for A728215?

Store A728215 in a tightly sealed container under an inert atmosphere at 2–8 °C, protected from moisture and light. For extended storage, −20 °C is recommended. Always consult the certificate of analysis (CoA) provided with the product for the specific expiry date and storage instructions, as actual shelf life depends on storage conditions.

References

1. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.; Wiley-Interscience: Hoboken, NJ, 2007. (General reference for Boc protecting group chemistry.)
2. Bodanszky, M.; Bodanszky, A. The Practice of Peptide Synthesis, 2nd ed.; Springer: Berlin, 1994. (General reference for peptide coupling methods.)
3. Albericio, F. Developments in peptide and amide synthesis. Curr. Opin. Chem. Biol. 2004, 8, 211–221. (Review of modern coupling reagents relevant to amino acid activation.) doi:10.1016/j.cbpa.2004.02.003

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