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Table 1. Racemization during SPPS of model peptides (% LDL isomers)ReagentH-Gly-Xxx-Phe-NH 2Z-Ile-Xxx-Pro-OHAsp Leu Ser Tyr Cys(Trt) HisBOP 0.71 0.11 0.32 0.22 5.1 1.1COMU 0.80 0.12 0.34 0.27 1.5 14.9COMU 1/2B 0.66 0.13 0.34 0.20 - -HATU 0.62 0.09 0.25 0.22 2.9 0.7HBTU 0.44 0.23 0.35 0.17 4.4 2.0HCTU 0.51 0.10 0.37 0.25 6.5 2.8PyBOP 0.42 0.11 0.53 0.20 5.0 1.3Pyclock 0.51 0.17 0.25 0.27 7.5 4.1DIC/Cl-HOBt 0.72 0.15 0.06 0.19 0.6 0.7DIC/HOAt 0.44 0.14 0.21 0.19 - -DIC/HOBt 0.40 0.08 0.07 0.22 0.6 2.3DIC/OXYMA 0.70 0.09 0.06 0.16 0.1 2.2equivalent in COMU mediated coupling did not reduce significantly racemization asreported earlier [8]. Use of traditional activating reagents such as DIC in combination withracemization suppressants especially Oxyma Pure as HOBt replacement are goodalternatives to minimize epimerization of amino acids including cysteine and histidineresidues during activation in solid phase peptide synthesis. This strategy can be a universalactivation protocol during automated peptide synthesis for most amino acids.References1. Goodman, M. Synthesis of Peptides and Peptidomimetics. Houben-Weyl, Methods of OrganicChemistry, Vol. E22, Thieme, Stuttgart-New York, 2002.2. Fenza, A., Rovero, P. Lett. Pept. Sci. 9, 125 (2002).3. El-Fahan, A., Subiros-Funosas, R., Albericio, F., J. Pept. Sci. Suppl. 14, 57 (2008).4. El-Fahan, A., Albericio, F. Chem. J. Pept. Sci. 16, 6 (2009).5. Moreno, J.A., Bayo-Puxan, N., Tulla-Puche, J., Luxemburg, Y., Philosof-Oppenheimer, R., Shvo,Y., Evenson, A., Albericio, F. poster presentation, 29 th European Peptide Symposium, Gdansk,Poland, 2006.6. Itoh, M. Bull Chem. Soc. Japan 46, 2219 (1973).7. Izdebski, J. Pol. J. Chem. 53, 1049 (1979).8. El-Fahan, A., Subiros-Funosas, R., Prohens, R., Albericio, F. Chem. Eur. J. 15, 9404 (2009).193