Criteria The CF 3 -group has to be attached rigidly to the peptide backbone.

1. MRE 30 PGLa-wt 25 15 20 16 17 15 18 10 5 0 -5 -10 -15 180 190 200 210 220 230 240 250 260 λ (nm) Synthesis of novel CF3-substituted α-amino acids as 19F-NMR labels P. K. Mykhailiuka, S. Afoninb, N. Gvozdovskaa, P. Wadhwanib, M. Berditschc, M. Ieronimoc, S. L. Grageb, A. S. Ulrichb,c, I. V. Komarova aKyiv National Taras Shevchenko University, Kyiv, Ukraine bInstitute of Biological Interfaces, Forschungszentrum Karlsruhe, Karlsruhe, Germany cInstitute of Organic Chemistry, University of Karlsruhe, Karlsruhe, Germany Contact: pashamk@gmx.de previously used 19F-NMR labels our ``new`` 19F-NMR labels Introduction CF3-substituted α-amino acids (CF3-AA) are highly useful as 19F-NMR labels. They are especiallyinformative in solid-state NMR studies of peptides in biomembranes. To be a ``good`` label the CF3-AA should meet several criteria. CF3(4/5)-Pro F3-Ala • Criteria • The CF3-grouphas to be attached rigidly to the peptide backbone. • The CF3-AA should be compatible with standard solid phase peptide synthesis (SPPS) protocols, react rapidly and without racemization. • 3. To replace a natural amino acid, the CF3-AA must not perturb the characteristics of the peptide (polarity, conformation, function). CF3-Phg CF3-Bpg F3-Aib CF3(3/4)-Pro Synthetic schemes Criterion 1: rigid structure (X-ray analysis) Criterion 2: successful peptide synthesis (RP-HPLC) Criterion 3: unperturbed peptide (CD, biological function) The antimicrobial α-helical peptide PGLa was used to test the incorporation of the „old“ CF3-Phg and the „new“ CF3-Bpg label. A single CF3-Bpg label was substituted in four different positions of the α-helical peptide PGLa: GMASKAGAI9A10GKI13A14KVALKAL-NH2 Circular dichroism showed that a single CF3-Bpg label does not perturb the conformation of the peptide. L-(CF3-Phg) racemizes during peptide synthesis. 2 diastereomers of 13-(CF3-Phg)-PGLa (containing D- and L-CF3-Phg) are formed. HPLC of 13-(CF3-Phg)-PGLa 9-(CF3Bpg)-PGLa RT (min) 10-(CF3Bpg)-PGLa 13-(CF3Bpg)-PGLa 14-(CF3Bpg)-PGLa wild type-PGLa HPLC of 13-(CF3-Bpg)-PGLa L-(CF3-Bpg) does not racemize during solid phase Fmoc peptide synthesis. The antimicrobial function of the four labelled analogues of PGLa was tested, and all minimal inhibitory concentrations were found to be identical to the wild type peptide RT (min) Conclusions References 1. Ulrich A. et al, Prog. NMR Spectr.2005, 46, 1-21. Several novel conformationally restricted CF3-labelled α-amino acids have been synthesized. These amino acids were designed as 19F-NMR labels for solid state NMR studies of membrane-bound peptides. CF3-Bpg has been demonstrated to fulfil all criteria for optimal use as a 19F-NMR. The application of the new CF3-Pro analogues as 19F-NMR labels is currently under investigation. 2. Glaser R. et al,Biophysical Journal2005, 88, 3392-3397. 3. Mykhailiuk, P. K.et al,Angew. Chem. Int. Ed. 2006, 45, 5659-5661. 4. Afonin, S.et al,J.Pept.Sci.2007, in print. 5. Mykhailiuk, P.K.et al,Angew. Chem. Int. Ed. 2007, submitted.