1. Pyridyl-alanine as a Hydrophilic, Aromatic Element in Peptide Structural Optimization
Piotr A Mroz, Diego Perez-Tilve, Fa Liu, Vasily Gelfanov, Richard D DiMarchi, John P Mayer J Med Chem. 2016 Sep 8;59(17):8061-7. doi: 10.1021/acs.jmedchem.6b00840. Epub 2016 Aug 25.
Glucagon (Gcg) 1 serves a seminal physiological role in buffering against hypoglycemia, but its poor biophysical properties severely complicate its medicinal use. We report a series of novel glucagon analogues of enhanced aqueous solubility and stability at neutral pH, anchored by Gcg[Aib16]. Incorporation of 3- and 4-pyridyl-alanine (3-Pal and 4-Pal) enhanced aqueous solubility of glucagon while maintaining biological properties. Relative to native hormone, analogue 9 (Gcg[3-Pal6,10,13, Aib16]) demonstrated superior biophysical character, better suitability for medicinal purposes, and comparable pharmacology against insulin-induced hypoglycemia in rats and pigs. Our data indicate that Pal is a versatile surrogate to natural aromatic amino acids and can be employed as an alternative or supplement with isoelectric adjustment to refine the biophysical character of peptide drug candidates.
2. The behavior of substrate analogues and secondary deuterium isotope effects in the phenylalanine ammonia-lyase reaction
A Gloge, B Langer, L Poppe, J Rétey Arch Biochem Biophys. 1998 Nov 1;359(1):1-7. doi: 10.1006/abbi.1998.0860.
Metacresol and glycine can be thought as a dissection of metatyrosine, which is an excellent substrate of phenylalanine ammonia-lyase (PAL) (B. Schuster and J. Rétey, PNAS 92, 8433, 1995). Whereas metacresol was a very weak inhibitor and glycine was inert, simultaneous addition of both compounds led to synergistic inhibition of PAL. [2H5]Phenylalanine as a substrate showed a kinetic deuterium isotope effect of 9% (kH/k2H = 1.09 +/- 0.01) while its Km value was identical to that of the unlabeled substrate. The following substrate analogues were synthesized and assayed with PAL: cyclooctatetraenyl (COT)-d,l)-alanine as well as 2-pyridyl-, 3-pyridyl-, and 4-pyridyl-(l)-alanines. While COT-(d,l)-alanine turned out to be a rather reluctant substrate, all three isomers of pyridyl-(l)-alanines were converted with a comparable or even higher Vmax than l-phenylalanine into the corresponding pyridyl acrylic acids. Their Km values were, however, an order of magnitude higher than that of the natural substrate. These results are discussed in terms of the novel mechanism which implies an electrophilic attack of the prosthetic dehydroalanine at the aromatic ring. The heats of formation of the putative sigma complexes of the electrophilic substitution at the pyridine ring have been calculated using semiempirical force-field methods. The results show the feasibility of the proposed mechanism also with the substrate analogues.
3. Biocompatible Macrocyclization between Cysteine and 2-Cyanopyridine Generates Stable Peptide Inhibitors
Christoph Nitsche, Hideki Onagi, Jun-Ping Quek, Gottfried Otting, Dahai Luo, Thomas Huber Org Lett. 2019 Jun 21;21(12):4709-4712. doi: 10.1021/acs.orglett.9b01545. Epub 2019 Jun 12.
Peptides featuring an N-terminal cysteine residue and the unnatural amino acid 3-(2-cyano-4-pyridyl)alanine (Cpa) cyclize spontaneously in aqueous solution at neutral pH. Cpa is readily available and easily introduced into peptides using standard solid-phase peptide synthesis. The reaction is orthogonal to all proteinogenic amino acids, including cysteine residues that are not at the N-terminus. A substrate peptide of the Zika virus NS2B-NS3 protease cyclized in this way produced an inhibitor of high affinity and proteolytic stability.
