D-Cyclopropylalanine: Properties, Synthesis & Research Uses

D-Cyclopropylalanine is a non-natural, conformationally constrained D-amino acid bearing a cyclopropyl side chain, valued in peptide chemistry, peptidomimetic design, and medicinal chemistry as a stereochemically defined building block.

Chemical Name

D-2-Amino-3-cyclopropylpropanoic acid

Stereochemistry

D-configuration (R) at the alpha carbon

CAS Number

No confirmed CAS listed in source material — see review flag

Side Chain Feature

Cyclopropylmethyl group; ring strain confers conformational rigidity

Key Application

Peptidomimetic and medicinal chemistry building block

Solubility

Generally soluble in water and dilute aqueous acid; specific solubility data needs verification

Chemical Structure and Stereochemistry

D-Cyclopropylalanine is a non-proteinogenic amino acid in which the side chain of alanine is extended by a cyclopropylmethyl group, yielding a three-membered carbocyclic ring appended to the beta carbon. The D-configuration denotes that the alpha-amino group adopts the (R) absolute configuration at the chiral centre, making it the enantiomer of the corresponding L-amino acid.

The cyclopropyl ring is distinguished by its inherent ring strain and unique orbital characteristics. The Walsh orbitals of cyclopropane provide partial pi-character to C–C bonds, which influences electronic interactions with adjacent functional groups and can modulate the pKa, conformation, and metabolic stability of molecules incorporating this moiety.

As a result, D-Cyclopropylalanine offers two layers of structural control: (1) the defined D-stereocenter dictates backbone geometry in peptide sequences, and (2) the cyclopropyl ring constrains rotational freedom of the side chain, reducing conformational entropy and potentially improving binding selectivity.

Synthetic Routes and Availability

Non-natural D-amino acids such as D-Cyclopropylalanine are typically accessed via asymmetric synthesis or by resolution of racemic mixtures. Common synthetic strategies include chiral phase-transfer catalysis, enzymatic resolution using D-selective aminoacylases, and asymmetric hydrogenation of prochiral dehydroamino acid precursors bearing the cyclopropylmethyl substituent.

An alternative route proceeds through the Strecker synthesis applied to cyclopropaneacetaldehyde, followed by stereochemical resolution to isolate the desired D-enantiomer. Diastereoselective alkylation of chiral glycine equivalents (e.g., Schöllkopf bis-lactim ethers or Seebach oxazolidinones) with cyclopropylmethyl electrophiles represents another robust laboratory approach, with subsequent hydrolysis and epimerization control to yield the D-series product.

For research laboratories, procurement of high-purity D-Cyclopropylalanine from specialist reagent suppliers such as Aladdin Scientific (SKU: C117163) is the most practical option, ensuring defined stereochemical purity and batch-to-batch consistency required for reproducible biological assays.

Applications in Peptide Chemistry and Drug Discovery

D-Cyclopropylalanine serves as a versatile building block in the design of peptidomimetics and biologically active peptides. Incorporation of D-amino acids into peptide sequences is a well-established strategy to resist proteolytic degradation by endogenous L-amino acid-specific proteases, thereby extending the in vivo half-life of therapeutic peptide candidates.

The cyclopropyl side chain adds an additional dimension of utility. Its conformational rigidity can pre-organise peptide backbones into specific secondary structural elements such as beta-turns and helical motifs, which is exploited in the design of receptor-selective ligands, enzyme inhibitors, and antimicrobial peptides. The cyclopropyl group also exhibits favourable metabolic properties, as it is less susceptible to cytochrome P450-mediated oxidative metabolism compared to open-chain alkyl analogues.

In medicinal chemistry, D-Cyclopropylalanine residues may be used to perform stereochemical probes of receptor binding sites, helping to map enantioselective pharmacophore requirements. The compound is also employed as a precursor for the synthesis of more complex cyclopropane-containing natural product analogues and as a handle for further side-chain functionalisation in diversity-oriented synthesis programmes.

Handling, Storage, and Quality Considerations

D-Cyclopropylalanine should be handled following standard laboratory safety protocols for amino acid reagents. Personal protective equipment including gloves, safety glasses, and a lab coat is recommended to avoid skin and eye contact with the solid or any derived solutions.

For storage, the compound should be kept in a tightly sealed container under cool, dry conditions, away from moisture, strong oxidising agents, and direct light. Refrigerated storage (2–8 °C) is typically recommended for long-term preservation of enantiopurity and chemical integrity; specific storage recommendations from the supplier certificate of analysis should always be followed.

Quality parameters critical for research use include: enantiomeric excess (ee), which should be verified by chiral HPLC or polarimetry; chemical purity assessed by NMR and HPLC; and identity confirmation via mass spectrometry. Researchers should request a certificate of analysis (CoA) confirming these parameters before use in sensitive biological or pharmaceutical assays. Aladdin Scientific provides product-specific quality documentation with each batch (SKU: C117163).

Frequently asked questions

What distinguishes D-Cyclopropylalanine from L-Cyclopropylalanine in biological applications?

D-Cyclopropylalanine carries the (R) configuration at the alpha carbon, the mirror image of the natural L-(S) form. In biological systems, this D-configuration makes the residue resistant to most proteolytic enzymes that are evolved to cleave L-peptide bonds, which is exploited to improve the metabolic stability of peptide therapeutics. Additionally, the two enantiomers often display different or even opposite receptor binding profiles, making D-Cyclopropylalanine a valuable stereochemical probe.

How should D-Cyclopropylalanine be dissolved for use in peptide coupling reactions?

D-Cyclopropylalanine is generally soluble in water and dilute aqueous acid (e.g., 0.1 M HCl); for organic synthesis applications, dissolution in DMF or DMSO may be used depending on the coupling protocol. Before use in solid-phase peptide synthesis, the amino acid typically requires Fmoc or Boc N-protection, and researchers should consult the relevant protection/deprotection protocols. Specific solubility data should be verified against the product CoA.

What analytical methods are recommended to verify the enantiomeric purity of D-Cyclopropylalanine?

Chiral high-performance liquid chromatography (HPLC) using an enantioselective stationary phase is the most reliable method for determining enantiomeric excess (ee) of D-Cyclopropylalanine. Polarimetry (optical rotation measurement) provides a rapid complementary check: the D-enantiomer will exhibit an optical rotation opposite in sign to the L-enantiomer. Nuclear magnetic resonance (NMR) spectroscopy with a chiral shift reagent can also be used. Researchers should request the supplier's CoA for reported ee values.

Can D-Cyclopropylalanine be used in Fmoc-based solid-phase peptide synthesis (SPPS)?

Yes, D-Cyclopropylalanine can be incorporated into peptides via Fmoc-based SPPS once the alpha-amino group is protected with the Fmoc group and any reactive functionalities are appropriately side-chain protected. The free amino acid (SKU: C117163) serves as the starting material for preparation of the Fmoc-protected derivative. Coupling efficiency should be monitored using Kaiser or chloranil tests, as sterically hindered or beta-branched residues may require extended coupling times or double-coupling protocols.

References

1. Voet D, Voet JG. Biochemistry, 4th ed. Wiley; 2011. (General amino acid stereochemistry and D-amino acids in biology.)
2. Gentilucci L, De Marco R, Cerisoli L. Chemical modifications designed to improve peptide stability: incorporation of non-natural amino acids, pseudo-peptide bonds, and cyclization. Curr Pharm Des. 2010;16(28):3185–3203. doi:10.2174/138161210793292555
3. Brackmann F, de Meijere A. Natural occurrence, syntheses, and applications of cyclopropyl-group-containing alpha-amino acids. Chem Rev. 2007;107(11):4493–4537. doi:10.1021/cr050917b
4. Nair RV, Baravkar SB, Ingole TS, Sanjayan GJ. Synthetic analogues of cyclopropane-containing natural products. Chem Commun. 2014;50:6526–6542.

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