The cyclic amino acid proline (Pro, P) represents unique features in terms of its conformational properties. This is even more true for cis-4-aminoprolines (cis-4-Amp): the amino group and the carboxylic acid are in proximity and possess a clamped stereochemistry, as they are attached to the circular, strained pyrrolidine system. The result is an intramolecular hydrogen bond which can exert a strong influence on the tertiary structure of the final peptide, stabilizing beta- and gamma-turns, respectively.

Two possibilities for hydrogen bond formation in cis-4-aminoproline.

Thus, cis 4-Amp can be used to induce both beta- and gamma-turns, depending on the positioning of the intramolecular hydrogen bond between the amino- and the carboxyl group. The gamma-turns play a role in initiating the formation of beta-sheets during protein folding. Beta- and gamma turns are also recognized as important sites for posttranslational modifications, particularly for phosphorylation and glycosylation. Moreover, replacing a native proline with 4-Amp can lead to significantly improved water solubility, due to the added polar amino group. Another fascinating application of 4-Amps involves building cyclic peptides around it and utilizing the amino group at position 4 as an anchor, i.e., by connecting it to a scaffold or carrier molecule.

The unique steric and stereoelectronic characteristics of amino and ammonium groups can be harnessed to create pH-responsive probes: For instance, in (2S,4S)-4-Amp, the configuration shifts from exo (chair) in alkaline conditions to endo (boat) in acidic pH. This change is supported by the formation of a transannular hydrogen bond when the primary amino group is protonated and generates a remarkable feature which enables the regulation of pH-dependent denaturation in peptides and peptide assemblies, such as collagens. A possible application of this effect is the controlled release of payloads like medications or effector molecules.

To introduce 4-Amp by solid-phase peptide synthesis, the amino groups require orthogonal protection, e.g. Boc and Fmoc. At Iris Biotech, various suitable derivatives are available (see related products).

Two examples for orthogonally protected amino-groups in 4-Amp.

Abbreviations: Fmoc = Fluorenylmethyloxycarbonyl; Boc = t-Butyloxycarbonyl; Alloc = Allyloxycarbonyl; Poc = Propargyloxycarbonyl.

→  You’re looking for a different Aminoproline not listed in our catalog? Get in contact for a custom synthesis! 

→ More Proline- and Pseudoproline molecules are summarized in our (Pseudo-)Prolines Flyer.

References:

N-α-benzoyl-cis-4-amino-L-proline: A γ-turn mimetic; T. P. Curran, N. M. Chandler, R. J. Kennedy, M. T. Keaney; Tetrahedron Letters 1996; 37: 1933-1936. https://doi.org/10.1016/0040-4039(96)00307-3

Total Synthesis and Antifungal Evaluation of Cyclic Aminohexapeptides; L. L. Klein, L. Li, H.-J. Chen, C. B. Curty, D. A. DeGoey, D. J. Grampovnik, C. L. Leone, S. A. Thomas, C. M. Yeung, K. W. Funk, V. Kishore, E. O. Lundell, D. Wodka, J. A. Meulbroek, J. D. Alder, A. M. Nilius, P. A. Lartey, J. J. Plattner; Bioorganic & Medicinal Chemistry 2000; 8: 1677-1696. https://doi.org/10.1016/S0968-0896(00)00097-3

The cis-4-Amino-L-proline Residue as a Scaffold for the Synthesis of Cyclic and Linear Endomorphin-2 Analogues; A. Mollica, F. Pinnen, A. Stefanucci, F. Feliciani, C. Campestre, L. Mannina, A. P. Sobolev, G. Lucente, P. Davis, J. Lai, S.-W. Ma, F. Porreca, V. J. Hruby; J. Med. Chem. 2012; 55: 3027-3035. https://doi.org/10.1021/jm201402v

cis-4-Amino-l-proline Residue as a Scaffold for the Synthesis of Cyclic and Linear Endomorphin-2 Analogues: Part 2; A. Mollica, F. Pinnen, A. Stefanucci, L. Mannina, A. P. Sobolev, G. Lucente, P. Davis, J. Lai, S.-W. Ma, F. Porreca, V. J. Hruby; J. Med. Chem. 2012; 55: 8477–8482. https://doi.org/10.1021/jm300947s

pH-Responsive Aminoproline-Containing Collagen Triple Helices; J. Egli, C. Siebler, B. Maryasin, R. S. Erdmann, C. Bergande, C. Ochsenfeld, H. Wennemers; Chemistry 2017; 23: 7938-44. https://doi.org/10.1002/chem.201701134

Application of (4R)-aminoproline in peptide engineering: conformational bias and pH-responsiveness revisited; V. Kubyshkin; New J Chem. 2022; 46: 9587-9594. https://doi.org/10.1039/D2NJ00305H

New 4-Aminoproline-Based Small Molecule Cyclopeptidomimetics as Potential Modulators of α4β1 Integrin; A. Sartori, K. Bugatti, E. Portioli, M. Baiula, I. Casamassima, A. Bruno, F. Bianchini, C. Curti, F. Zanardi, L. Battistini; Molecules 2021; 26: 6066-6087. https://doi.org/10.3390/molecules26196066