We use cookies to improve your experience. By continuing to browse this site, you accept our cookie policy.×

Azapeptides and their therapeutic potential

    Caroline Proulx

    Département de Chimie, Université de Montréal, CP 6128, Succursale Centre Ville, Montréal, Québec, H3C3J7, Canada

    ,
    David Sabatino

    Département de Chimie, Université de Montréal, CP 6128, Succursale Centre Ville, Montréal, Québec, H3C3J7, Canada

    Department of Chemistry and Biochemistry, Seton Hall University, 400 South Orange Avenue, South Orange, NJ 07079, USA

    ,
    Robert Hopewell

    Département de Chimie, Université de Montréal, CP 6128, Succursale Centre Ville, Montréal, Québec, H3C3J7, Canada

    ,
    Jochen Spiegel

    Département de Chimie, Université de Montréal, CP 6128, Succursale Centre Ville, Montréal, Québec, H3C3J7, Canada

    Institute for Advanced Study Technische Universität München, Department Chemie, Lichtenbergstrasse 4, 85747 Garching, Germany

    ,
    Yésica García Ramos

    Département de Chimie, Université de Montréal, CP 6128, Succursale Centre Ville, Montréal, Québec, H3C3J7, Canada

    &
    Published Online:https://doi.org/10.4155/fmc.11.74

    Azapeptides are peptide analogs in which one or more of the amino residues is replaced by a semicarbazide. This substitution of a nitrogen for the α-carbon center results in conformational restrictions, which bend the peptide about the aza-amino acid residue away from a linear geometry. The resulting azapeptide turn conformations have been observed by x-ray crystallography and spectroscopy, as well as predicted based on computational models. In biologically active peptide analogs, the aza-substitution has led to enhanced activity and selectivity as well as improved properties, such as prolonged duration of action and metabolic stability. In light of these characteristics, azapeptides have found important uses as receptor ligands, enzyme inhibitors, drugs, pro-drugs, probes and imaging agents. Recent improvements in synthetic methods for their procurement have ushered in a new era of azapeptide chemistry. This review aims to provide a historical look at the development of azapeptide science along with a focus on recent developments and perspectives on the future of this useful tool for medicinal chemistry.

    Papers of special note have been highlighted as: ▪ of interest ▪▪ of considerable interest

    Bibliography

    • Gray CJ, Quibell M, Baggett N, Hammerle T. Incorporation of azaglutamine residues into peptides synthesised by the ultra-high load solid (gel)-phase technique. Int. J. Peptide Protein Res.40(5),351–362 (1992).
    • Liley M, Johnson T. Solid phase synthesis of azapeptides utilising reversible amide bond protection to prevent hydantoin formation. Tetrahedron Lett.41(20),3983–3985 (2000).
    • Ahn IA, Woong Kim S, Ro S. Solid phase synthesis of azapeptides using an automatic synthesizer. Mol. Divers.4(1),23–24(1998).
    • Verhelst SHL, Witte MD, Arastu-Kapur S, Fonovic M, Bogyo M. Novel aza peptide inhibitors and active-site probes of papain-family cysteine proteases. Chem. Bio. Chem.7(6),943–950 (2006).
    • Melendez RE, Lubell WD. Aza-amino acid scan for rapid identification of secondary structure based on the application of N-Boc-aza1-dipeptides in peptide synthesis. J. Am. Chem. Soc.126(21),6759–6764 (2004).▪ Strategy developed for aza amino acid scanning.
    • Nowick JS, Powell NA, Nguyen TM, Noronha G. An improved method for the synthesis of enantiomerically pure amino acid ester isocyanates. J. Org. Chem.57(26),7364–7366 (1992).
    • André F, Marraud M, Tsouloufis T, Tzartos SJ, Boussard G. Triphosgene: an efficient carbonylating agent for liquid and solid-phase aza-peptide synthesis. Application to the synthesis of two aza-analogues of the AChR MIR decapeptide. J. Pept. Sci.3(6),429–441 (1997).
    • Frochot C, Vanderesse R, Driou A, Linden G, Marraud M, Thong Cung M. A solid-phase synthesis of three aza-, iminoaza- and reduced aza-peptides from the same precursor. Lett. Pept. Sci.4(4),219–225 (1997).
    • Bourguet CB, Proulx C, Klocek S, Sabatino D, Lubell WD. Solution-phase submonomer diversification of aza-dipeptide building blocks and their application in aza-peptide and aza-DKP synthesis. J. Pept. Sci.16(6),284–296 (2010).
    • 10  Sabatino D, Proulx C, Klocek S et al. Exploring side-chain diversity by submonomer solid-phase aza-peptide synthesis. Org. Lett.11(16),3650–3653 (2009).▪▪ Introduction to the submonomer azapeptide synthesis approach.
    • 11  Gibson C, Goodman SL, Hahn D, Holzemann G, Kessler H. Novel solid-phase synthesis of azapeptides and azapeptoides via FMOC-strategy and its application in the synthesis of RGD-mimetics. J. Org. Chem.64(20),7388–7394 (1999).
    • 12  Sulyok GAG, Gibson C, Goodman, SL, Hölzemann G, Wiesner M, Kessler H. Solid-phase synthesis of a nonpeptide RGD mimetic library: new selective avb3 integrin antagonists. J. Med. Chem.44(12),1938–1950 (2001).
    • 13  Malachowski WP, Tie C, Wang K, Broadrup RL. The synthesis of azapeptidomimetic β-lactam molecules as potential protease inhibitors. J. Org. Chem.67(25),8962–8969 (2002).
    • 14  Boeglin D, Lubell WD. Aza-amino acid scanning of secondary structure suited for solid-phase peptide synthesis with fmoc chemistry and aza-amino acids with heteroatomic side chains. J. Comb. Chem.7(6),864–878 (2005)
    • 15  Boeglin D, Xiang Z, Sorenson NB, Wood MS, Haskell-Luevano C, Lubell WD. Aza-scanning of the Potent melanocortin receptor agonist Ac-His-D-Phe-Arg-Trp-NH2. Chem. Biol. Drug Des.67(4),275–283 (2006).
    • 16  Freeman NS, Hurevich M, Gilon C. Synthesis of N´-substituted Ddz-protected hydrazines and their application in solid phase synthesis of aza-peptides. Tetrahedron65(8),1737–1745 (2009).
    • 17  Han H, Janda KD. Azatides: solution and liquid phase syntheses of a new peptidomimetic. J. Am. Chem. Soc.118(11),2539–2544 (1996).
    • 18  Han H, Yoon J, Janda KD. Investigations of azapeptides as mimetics of Leu-enkephalin. Bioorg. Med. Chem. Lett.8(1),117–120 (1998).
    • 19  Hansen TK. Synthesis of azapeptides from hindered amines leading to novel growth hormone secretagogues. Tetrahedron Lett.40(51),9119–9120 (1999).
    • 20  Randolph JT, Zhang X, Huang PP et al. Synthesis, antiviral activity, and conformational studies of a P3 aza-peptide analog of a potent macrocyclic tripeptide HCV protease inhibitor. Bioorg. Med. Chem. Lett.18(8),2745–2750 (2008).
    • 21  André F, Boussard G, Bayeul D, Didierjean C, Aubry A, Marraud M. Aza-peptides II. X-ray structures of aza-alanine and aza-asparagine-containing peptides. J. Pept. Res.49(6),556–562 (1997).
    • 22  Zega A, Mlinsek G, Sepic P et al. Design and structure–activity relationship of thrombin inhibitors with an azaphenylalanine scaffold: potency and selectivity enhancements via P2 optimization. Bioorg. Med. Chem.9(10),2745–2756 (2001).
    • 23  Bailey MD, Halmos T, Goudreau N, Lescop E, Llinàs-Brunet M. Novel azapeptide inhibitors of hepatitis C virus serine protease. J. Med. Chem.47(15),3788–3799 (2004).
    • 24  Wieczerzak E, Drabik P, Łankiewicz L et al. Azapeptides structurally based upon inhibitory sites of cystatins as potent and selective inhibitors of cysteine proteases. J. Med. Chem.45(19),4202–4211(2002).
    • 25  Mhidia R, Melnyk O. Selective cleavage of an azaGly peptide bond by copper(II). Long-range effect of histidine residue. J. Pept. Sci.16(3),141–147(2010).
    • 26  Boeglin D, Hamdan FF, Melendez RE et al. Calcitonin gene-related peptide analogues with aza and indolizidinone amino acid residues reveal conformational requirements for antagonist activity at the human calcitonin gene-related peptide 1 receptor. J. Med. Chem.50(6),1401–1408(2007).
    • 27  Proulx C, Lubell WD. Solid-phase synthesis of aza-proline analogs of GHRP-6. Peptides: Breaking Away. Proceedings of the 21st American Peptide Symposium. Lebl M (Ed.). Prompt Scientific Publishing, San Diego, CA, USA 56–57 (2009).
    • 28  Semple JE, Rowley DC, Brunck TK, Ripka WC. Synthesis and biological activity of P2-P4 azapeptidomimetic P1-argininal and P1-ketoargininamide derivatives: a novel class of serine protease inhibitors. Bioorg. Med. Chem. Lett.7(3),315–320 (1997).
    • 29  Zouikri M, Vicherat A, Aubry A, Marraud M, Boussard G. Azaproline as a β-turn-inducer residue opposed to proline. J. Pept. Res.52(1),19–26(1998).
    • 30  de los Santos JM, Lopez Y, Aparicio D, Palacios F. A convenient synthesis of substituted pyrazolidines and azaproline derivatives through highly regio- and diastereoselective reduction of 2-pyrazolines. J. Org. Chem.73(2),550–557 (2007).
    • 31  Mish MR, Guerra FM, Carreira EM. Asymmetric dipolar cycloadditions of Me3SiCHN2. Synthesis of a novel class of amino acids: azaprolines. J. Am. Chem. Soc.119(35),8379–8380 (1997).
    • 32  O’Donnell MJ, Zhou C, Scott WL. Solid-phase unnatural peptide synthesis (UPS). J. Am. Chem. Soc.118(25),6070–6071 (1996).
    • 33  Bourguet CB, Sabatino D, Lubell WD. Benzophenone semicarbazone protection strategy for synthesis of aza-glycine containing aza-peptides. Pept. Sci.90(6),824–831(2008).
    • 34  Proulx C, Lubell WD. Aza-1,2,3-triazole-3-alanine synthesis via copper-catalyzed 1,3-dipolar cycloaddition on aza-progargylglycine. J. Org. Chem.75(15),5385–5387(2010).
    • 35  Proulx C, Lubell WD. Copper-catalyzed N-arylation of semicarbazones for the synthesis of aza-arylglycine-containing aza-peptides. Org. Lett.12(13),2916–2919 (2010).
    • 36  Gante J, Neunhoeffer H, Schmidt A. Peptide analog systems. 9. Synthesis of 1,2,4-triazines. 16. bridged azapeptides, a class of novel 1,4,5,6-tetrahydro-1,2,4-triazin-3(2H)ones. J. Org. Chem.59(21),6487–6489 (1994).
    • 37  Dyker H, Scherkenbeck J, Gondol D, Goehrt A, Harder A. Azadepsipeptides: synthesis and evaluation of a novel class of peptidomimetics. J. Org. Chem.66(11),3760–3766 (2001).
    • 38  Thormann M, Hofmann HJ. Conformational properties of azapeptides. J. Mol. Struct. (Theochem).469(1–3),63–76 (1999).
    • 39  Jeffrey GA. The structures of some small molecules. Ab initio molecular orbital calculations versus low temperature neutron diffraction crystal structure analyses. J. Mol. Struct. (Theochem).108(1–2),1–15 (1984).
    • 40  Ramondo F, Bencivenni L. Molecular conformation of isolated and hydrogen bonded N,N´-diformohydrazide: an ab initio study. J. Chem. Soc. Perkin Trans. 2.9,1797–1804 (1995).
    • 41  Reynolds CH, Hormann E. Theoretical study of the structure and rotational flexibility of diacylhydrazines: implications for the structure of nonsteroidal ecdysone agonist and azapeptides. J. Am. Chem. Soc.118(39),9395–9401 (1996).
    • 42  Chakravorty S, Reynolds CH. Improved AMBER torsional parameters for the N-N rotational barrier in diacylhydrazines. J. Mol. Graphics Mod.17,315–324 (1999).
    • 43  Bryantsev VS, Firman TK, Hay BP. Conformational analysis and rotational barriers of alkyl- and phenyl-substituted urea derivatives. J. Phys. Chem. A.109(5),832–842 (2005).
    • 44  Semetey V, Hemmerlin C, Didierjean C et al. Unexpected stability of the urea cis-trans isomer in urea-containing model pseudopeptides. Org. Lett.3(24),3843–3846 (2001).
    • 45  Bishop GJ, Price BJ, Sutherland IO. Torsional barriers in N,N´-diacylhydrazines. J. Chem. Soc. Chem. Commun.14,672–674 (1967).
    • 46  Fletcher JR, Sutherland IO. Conformational changes in tetra-alkylhydrazines. J. Chem. Soc. Chem. Commun.13,706–708 (1969).
    • 47  Lee HJ, Lee MH, Choi YS, Park HM, Lee KB. NBO approach to evaluate origin of rotational barrier of diformylhydrazine. J. Mol. Struct. (Theochem).631(1–3),101–110 (2003).
    • 48  Lee HJ, Lee KB, Ahn IA, Ro S, Choi KH, Choi YS. Role of azaamino acid residue in β-turn formation and stability in designed peptide. J. Pept. Res.56(1),35–46 (2000).
    • 49  Ro S, Yoon CJ. Conformational preference of acetyl-azaalanine-N-methyl amide. Z. Phys. Chem.214(12),1699–1706 (2000).
    • 50  Lee HJ, Choi KH, Ahn IA et al. The β-turn preferential solution conformation of a tetrapeptide containing an azaamino acid residue. J. Mol. Struct.569(1–3),43–54 (2001).
    • 51  Lee HJ, Song JW, Choi, YS, Park HM, Lee KB. A theoretical study of conformational properties of N-methyl azapeptide derivatives. J. Am. Chem. Soc.124(40),11881–11893 (2002).
    • 52  Lee HJ, Jung HJ, Kim JH, Park HM, Lee KB. Conformational preference of azaglycine-containing dipeptides studied by PCM and IPCM methods. Chem. Phys.294(2),201–210 (2003).
    • 53  Lee HJ, Park HM, Lee KB. The β-turn scaffold of tripeptide containing an azaphenylalanine residue. Biophys. Chem.125(1),117–126 (2007).
    • 54  Richardson JS. The anatomy and taxonomy of protein structure. Adv. Protein Chem.34,167–339 (1981).
    • 55  Hutchinson EG, Thornton JM. A revised set of potentials for β-turn formation in proteins. Protein Sci.3,2207–2216 (1994).
    • 56  Zhang WJ, Berglund A, Kao JL, Couty JP, Gershengorn MC, Marshall GR. Impact of azaproline on amide cis-trans isomerism: conformational analyses and NMR studies of model peptides including TRH analogues. J. Am. Chem. Soc.125(5),1221–1235 (2003).
    • 57  Che Y, Marshall GR. Impact of azaproline on peptide conformation. J. Org. Chem.69(26),9030–9042 (2004).
    • 58  André F, Vicherat A, Boussard G, Aubry A, Marraud M. Aza-peptides. III. Experimental structural analysis of aza-alanine and aza-asparagine-containing peptides. J. Pept. Res.50(5),372–381 (1997).
    • 59  Lecoq A, Boussard G, Marraud M, Aubry A. Crystal state conformation of three azapeptides containing the azaproline residue, a β-turn regulator. Biopolymers33(7),1051–1059 (1993).
    • 60  Marraud M, Aubry A. Crystal structures of peptides and modified peptides. Pept. Sci.40(1),45–83 (1996).▪ Review containing x-ray analyses of azapeptides.
    • 61  Benatalah Z, Aubry A, Boussard G, Marraud M. Evidence for a β-turn in an azadipeptide sequence. Synthesis and crystal structure of ButCO-Pro-AzaAla-NHPri. Int. J. Pept. Protein. Res.38(6),603–605 (1991).
    • 62  Gante J, Krug M, Lauterbach G, Weitzel R, Hiller W. Synthesis and properties of the first all-aza analogue of a biologically active peptide. J. Pept. Sci.1(3),201–206 (1995).
    • 63  Hemmerlin C, Cung MT, Boussard G. Synthesis and conformational preferences in solution and crystalline states of an aza-tripeptide. Tetrahedron Lett.42(30),5009–5012 (2001).
    • 64  André F, Marraud M, Boussard G. Synthesis and structure of azasx-pro-containing aza-peptides. Tetrahedron Lett.37(2),183–186 (1996).
    • 65  Bac A, Rivoal K, Cung M et al. Conformational disturbance induced by AzPro/Pro substitution in peptides. Lett. Pept. Sci.4(4),251–258 (1997).
    • 66  Kelly SM, Jess TC, Price NC. How to study proteins by circular dichroism. Biochim. Biophys. Acta Proteins Proteomics1751(2),119–139 (2005).
    • 67  Bush CA, Sarkar SK, Kopple KD. Circular dichroism of β turns in peptides and proteins. Biochemistry17(23),4951–4954 (1978).
    • 68  Gante J. Azapeptides. Synthesis6,405–413 (1989).▪ Early review on azapeptides.
    • 69  Hess H-J, Moreland WT, Laubach GD. N-[2-isopropyl-3-(L-aspartyl-L-arginyl)-carbazoyl]-L- tyrosyl-L-valyl-L-histidyl-L-prolyl-L-phenylalanine, an isostere of bovine angiotensin II. J. Am. Chem. Soc.85(24),4040–4041 (1963).
    • 70  Bolla M, Collette L, Blank L et al. Long-term results with immediate androgen suppression and external irradiation in patients with locally advanced prostate cancer (an EORTC study): a phase III randomised trial. The Lancet360(9327),103–108(2002).
    • 71  Zega A, Urleb U. Azapeptides. Acta Chim. Slov.49,640–662 (2002).
    • 72  Zega A. Azapeptides as pharmacological agents. Curr. Med. Chem.12,589–597 (2005).
    • 73  Hart M, Beeson C. Utility of azapeptides as major histocompatibility complex class II protein ligands for T-cell activation. J. Med. Chem.44(22),3700–3709 (2001).
    • 74  Andurkar SV, Béguin C, Stables JP, Kohn H. Synthesis and structural studies of aza analogues of functionalized amino acids: new anticonvulsant agents. J. Med. Chem.44(9),1475–1478 (2001).
    • 75  Wipf P, Li W, Adeyeye CM, Rusnak JM, Lazo JS. Synthesis of chemoreversible prodrugs of ara-C with variable time-release profiles. Biological evaluation of their apoptotic activity. Bioorg. Med. Chem.4(10),1585–1596 (1996).
    • 76  Weber D, Berger C, Eickelmann P, Antel J, Kessler H. Design of selective peptidomimetic agonists for the human orphan receptor BRS-3. J. Med. Chem.46(10),1918–1930 (2003).
    • 77  Perona JJ, Craik CS. Structural basis for substrate specificity in the serine proteases. Protein Sci.4(3),337–360 (1995).
    • 78  Otto HH, Schirmeister T. Cysteine proteases and their inhibitors. Chem. Rev.97(1),133–172 (1997).
    • 79  Kwong AD, Kim JL, Rao G, Lipovsek D, Raybuck SA. Hepatitis C virus NS3/4A protease. Antiviral Res.40(1–2),1–18 (1998).
    • 80  Lundblad RL, Bradshaw RA, Gabriel D, Ortel TL, Lawson J, Mann KG. A review of the therapeutic uses of thrombin. Thromb. Haemost.91(5),851–860 (2004).
    • 81  Sajid M, McKerrow JH. Cysteine proteases of parasitic organisms. Mol. Biochem. Parasit.120(1),1–21 (2002).
    • 82  Barrett A, Rawlings ND. Evolutionary lines of peptidases. Biol. Chem.382(5),727–733 (2001).
    • 83  Joyce JA, Baruch A, Chehade J et al. Cathespin cysteine proteases are effectors of invasive growth and angiogenesis during multistage tumorigenesis. Cancer Cell5(5),443–453 (2004).
    • 84  Iwata Y, Mort JS, Tateishi H, Lee ER. Macrophage cathespin L, a factor in the erosion of subchondral bone in rheumatoid arthritis. Arthritis Rheum.40(3),499–509 (1997).
    • 85  Lacaille F, Kaleta J, Bromme D. Human and parasitic papain-like cysteine proteases: their role in the physiology and pathology and recent developments in inhibitor design. Chem. Rev.102(12),4459–4488 (2002).
    • 86  Denault JB, Salvesen GS. Caspases: keys in the ignition of cell death. Chem. Rev.102(12),4489–4500 (2002).
    • 87  Bilsland J, Harper S. Caspases and neuroprotection. Curr. Opin. Investig. Drugs3(12),1745–1752 (2002).
    • 88  Smalley JW, Birss AJ, Kay HM, McKee AS, Marsh PD. The distribution of trypsin-like enzyme activity in cultures of a virulent and an avirulent strain of Bacteroides gingivalis W50. Oral Microbiol. Immunol.4(3),178–181 (1989).
    • 89  Liu C, Sun CZ, Huang HN, Janda K, Edgington T. Overexpression of legumain in tumors is significant for invasion/metastasis and a candidate enzymatic target for prodrug therapy. Cancer Res.63(11),2957–2964 (2003).
    • 90  Mitchell WM, Harrington WF. Clostripain. Methods Enzymol.19,635–642 (1970).
    • 91  Dutta AS, Giles M. Polypeptides. Part XIV. A comparative study of the stability towards enzymes of model tripeptides containing α-aza-amino acids, L-amino acids, and D-amino acids. J. Chem. Soc., Perkin Trans. 1244–248 (1976).
    • 92  Dutta AS, Giles M, Williams J. Inhibitors of porcine pancreatic elastase. peptides incorporating α-aza-amino acid residues in the P1 position. J. Chem. Soc. Perkin Trans. 11655–1663 (1986).
    • 93  Zhang R, Durkin JP, Windsor WT. Azapeptides as inhibitors of the hepatitis C virus NS3 protease. Bioorg. Med. Chem. Lett.12(7),1005–1008 (2002).
    • 94  Powers JC, Boone R, Carroll DL et al. Reaction of azapeptides with human leukocyte elastase and porcine pancreatic elastase J. Biol. Chem.259(7),4288–4294 (1984).
    • 95  Magrath J, Abeles RH. Cysteine protease inhibition by azapeptide esters J. Med. Chem.35(23),4279–4283 (1992).
    • 96  Xing R, Hanzlik RP. Azapeptides as inhibitors and active site titrants for cysteine proteinases. J. Med. Chem.41(8),1344–1351(1998).
    • 97  Asgian JL, James KE, Li ZZ et al. Aza-peptide epoxides: a new class of inhibitors selective for clan CD cysteine proteases J. Med. Chem.45(23),4958–4960 (2002).
    • 98  Frizler M, Stirnberg M, Sisay MT, Gütschow M. Development of nitrile-based peptidic inhibitors of cystein cathepsins. Curr. Top. Med. Chem.10,294–322 (2010).
    • 99  Löser R, Frizler M, Schilling K, Gütschow M. Azadipeptide nitriles : highly potent and proteolytically stable inhibitors of papain-like cysteine proteases. Angew. Chem. Int. Ed.47,4331–4334 (2008).
    • 100  Frizler M, Lohr F, Furtmann N, Kläs J, Gütschow M. Structural optimization of azadipeptide nitriles strongly increases association rates and allows the development of selective cathepsin inhibitors. J. Med. Chem.54(1),396–400 (2011).
    • 101  James KE, Asgian JL, Li ZZ et al. Design, synthesis, and evaluation of aza-peptide epoxides as selective and potent inhibitors of caspases-1, -3, -6, and -8 J. Med. Chem.47(6),1553–1574 (2004).
    • 102  Ovat A, Muindi F, Fagan C et al. Aza-peptidyl Michael acceptors and epoxide inhibitors- potent and selective inhibitors of Schistosoma mansoni and Ixodes ricinus legumains (asparaginyl endopeptidases) J. Med. Chem.52(22),7192–7210 (2009).
    • 103  Ekici OD, Li ZZ, Campbell AJ et al. Design, synthesis and evaluation of aza-peptide Michael acceptors as selective and potent inhibitors of caspases-2, -3, -6, -7, -8, -9 and -10. J. Med. Chem.49(19),5728–5749 (2004).
    • 104  Sexton KB, Kato D, Berger AB, Fonovic M, Verhelst SHL, Bogyo M. Specificity of aza-peptide electrophile activity-based probes of caspases. Cell Death Diff.14(4),727–732 (2007).▪ Application of azapeptide inhibitors as probes.
    • 105  Ekici OD, Gotz MG, James KE et al. Aza-peptide Michael acceptors: a new class of inhibitors specific for caspases and other clan CD cysteine proteseas. J. Med. Chem.47(8),1889–1892 (2004).
    • 106  Gotz MG, James KE, Hansell E et al. Aza-peptidyl Michael acceptors. a new class of potent and selective inhibitors of asparaginyl endopeptidases (legumains) from evolutionary diverse pathogens. J. Med. Chem.51(9),2816–2832 (2008).
    • 107  Ganesan R, Jelakovic S, Campbell AJ et al. Exploring the S4 and S1 prime subsite specificities in caspase-3 with aza-peptide epoxide inhibitors. Biochemistry45(30),9059–9067 (2006).
    • 108  Kato D, Verhelst SHL, Sexton KB, Bogyo M. A general solid-phase method for the preparation of diverse aza-peptide probes against cysteine proteases. Org. Lett.7(25),5649–5652 (2005).
    • 109  Lee J, Bogyo M. Development of near-infrared fluorophore (NIRF)-labeled activity-based probes for in vivo imaging of legumain. Chem. Biol.5(2),233–243 (2010).