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Fig. 1. CD spectrum of oxytocin (OT).Fig. 2. UV spectrum of tocinamide I2 (OT6I2)and tocinamide I2(OT6I2).Hydrogenolysis (Pd/C) [3,4], various bases [1,2], AlCl 3 /Toluene [5], catalytic amount ofDBU/C8SH [6], MeONa/mercaptoacetic acid [7], elevated temperature (130 o C) [8] andresin bound piperazine and other resin supported scavenging agents were tested. DBF athigher concentration polymerizes and if not fully scavenged, reacts reversibly with theamino groups on the peptide chain producing secondary peptide-amines. Tert-butylaminehas the properties convenient for Fmoc deprotection. It is a strong base (pK a 10.7), and itsreactivity towards amide formation is limited due to its bulky chain. Boiling point of TBAis 46 o C and therefore it can be evaporated very easily.TBA solutions (30% in DCM, THF, dioxan, DMF, ACN), or neat TBA were used forFmoc deprotection in solution synthesis. Peptides having free amino group can be usuallyprecipitated by ether, heptane, or petroleum ether from the reaction mixture. For theimprovement of solubility in these solvents, DBF should be scavenged by C18-SH to forman adduct which can be then easily extracted. Unpleasant odor of C18-SH is wellacceptable in comparison to other commonly used thiols.Circular dichroism of the diiodinated compound OT6I2 (measured on Jasco J-815spectrometer in neutral buffer (PBS 10mM pH = 7, quartz cell 0.1cm) shows the intensenegative band at 190-210 nm and the smaller positive band at 220-250 nm, both nearlyidentical to CD spectra of oxytocin (see Figure 1). Finding these bands red shifted by about10 nm for OT6I2 as compared to OT conforms to the effect of iodinated tyrosine aromaticring. The band due to iodinated tyrosine nucleus is also discernible in absorption spectrumat ~310 nm (range 280-350 nm, measured on Jasco J-815 spectrometer in neutral buffer(PBS 10mM pH = 7, quartz cell 1cm). A similarity between CD spectra of the complete OTnonapeptide and just the ring part with the modified tyrosine indicates that a conformationof both cyclic parts remains similar and the C-terminal tripeptide of oxytocin has only aminor effect on its spectral properties.AcknowledgmentsThe investigation was supported by MSM 0021620806 G.A. Czech. Acad. Sci. KAN 200520703 and200100801 and by Grant Z4 055 0506.References1. Fields, G.B. Methods in Molecular Biology 35, Peptide Synthesis Protocols, (Pennington M.W.,Dunn, B.M., Eds.), Humana Press (1994).2. Takahashi, D., patent application number 20100184952 USPC Class 530333.3. Carpino, L.A., Han, G.Y. J. Org. Chem. 37, 3404-3409 (1972).4. Maegawa, T., Fujiwara, Y., Ikawa, T., Hisashi, H., Mongushi, Y., Sajiki, H. Amino Acids 36, 493-499 (2009).5. Leggio, A., Liguori, A., Napoli, A., Siciliano, C., Sindona, G. Eur. J. Org. Chem. 573-575 (2000).6. Sheppeck, J.E., Kar, H., Hong, H. Tetrahedron Letters 41, 5329-5333 (2000).7. De Marco, R., et al. Amino Acids DOI 10.1007/s00726-009-0267-2.8. Hoeck, S., Marti, R., Riedl, R., Simeunovic, M. Chimia 64, 200-202 (2010).55