The application of peptides as therapeutic agents has significantly increased over the last years bolstered by improvements in peptide manufacturing. However, their inherent susceptibility to proteolytic degradation leading to rapid elimination in vivo has traditionally impeded their broader use.

It is reported that the incorporation of beta, beta amino acid analogues at the P1’ position, directly C-terminal of the enzyme cleavage site, rendering peptides highly resistant to serine protease degradation without significantly impacting their biological activity or secondary structure, as shown by circular dichroism and receptor activation in comparison to their “original” counterparts. This includes stability towards dipeptidyl peptidase IV (DPP IV), dipeptidyl peptidase 8 (DPP 8), fibroblast activation protein alpha (FAP alpha), alpha-lytic protease (alpha LP), trypsin, and chymotrypsin.

Comparative hydrolysis studies of hexapeptides carrying either the natural amino acid residues Leu or Ile at the P1’ position or the beta, beta dimethylated derivative showed that already after 30 min, more than 70% of AP(Leu)SWS and AP(Ile)SWS were hydrolyzed whereas the modified sequence was completely resistant to DPP IV-mediated cleavage during that time.

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Besides its improvements for proteolytic stability, the presented building block (FAA5040) can easily be modified via its side chain double bond. Alkenes can undergo a variety of reactions, which can be classified according to their reaction mechanism. Alkenes can act as nucleophiles resulting in the formation of a carbocation upon attacking an electrophile, e.g. as given in the addition of H-Br to an alkene. Reactions can also proceed via a three-membered ring intermediate. This intermediate is then attacked at the most substituted carbon by a nucleophilic backside attack leading to inverted stereochemistry. Reactions in this category include the addition of halogens, oxymercuration, or the opening of epoxides. The concerted syn pathway includes hydroboration, hydrogenation, epoxidation, dihydroxylation, cyclopropanation, dichlorocyclopropanation.

Another highly important reaction in organic chemistry is the olefin metathesis which was elucidated by Yves Chauvin, Robert H. Grubbs, and Richard R. Schrock and awarded the 2005 Nobel Prize in Chemistry. This reaction allows the scission and reconnection of alkene fragments under the formation of a new carbon-carbon bond via metal catalysis. One known example is the Grubbs catalyst, named after its inventor, a ruthenion(II) carbenoid complex.  Types of olefin metathesis processes includes e.g. cross metathesis, ring-opening metathesis and ring-closing metathesis.

This selection represents the huge variety of possibilities to modify alkene bonds.

References:

A General Method for Making Peptide Therapeutics Resistant to Serine Protease Degradation: Application to Dipeptidyl Peptidase IV Substrates; K. R. Heard, W. Wu, Y. Li, P. Zhao, I. Woznica, J. H. Lai, M. Beinborn, D. G. Sanford, M. T. Dimare, A. K. Chiluwal, D. E. Peters, D. Whicher, J. L. Sudmeier, W. W. Bachovchin; J. Med. Chem. 2013; 56(21): 8339-8351. https://doi.org/10.1021/jm400423p.

Synthesis and Biological Activity of Analogues of the Antimicrotubule Agent N,beta,beta-Trimethyl-L-phenylalanyl-N1-[(1S,2E)-3-carboxy-1-isopropylbut-2-enyl]-N1,3-dimethyl-L-valinamide (HTI-286); A. Zask, G. Birnberg, K. Cheung, J. Kaplan, C. Niu, E. Norton, R. Suayan, A. Yamashita, D. Cole, Z. Tang, G. Krishnamurthy, R. Williamson, G. Khafizova, S. Musto, R. Hernandez, T. Annable, X. Yang, C. Discafani, C. Beyer, L. M. Greenberger, F. Loganzo, S. Ayral-Kaloustian; J. Med. Chem. 2004; 47: 4774-4786. https://doi.org/10.1021/jm040056u.

Total synthesis of the large non-ribosomal peptide polytheonamide B; M. Inoue, N. Shinohara, S. Tanabe, T. Takahashi, K. Okura, H. Itoh, Y. Mizoguchi, M. Iida, N. Lee; S. Matsuoka; Nat. Chem. 2010; 2: 280-285. https://doi.org/10.1038/nchem.554.