Design of peptides: crystal and molecular structure of a 3(10)-helical peptide N-Boc-L-Phe-dehydro-Phe-L-Val-L-Phe-dehydro-Phe-L-Val-OCH3.

Highly specific peptide structures can be designed by inserting dehydro residues into peptide sequences. The peptide N-Boc-L-Phe-dehydro-Phe-L-Val-L-Phe-dehydro-Phe-L-Val- OCH3, synthesized by conventional procedures, crystallizes from methanol-water mixtures at 4 degrees C in the tetragonal space group P4(3) with cell parameters a = b = 13.829 +/- 0.003 A, c = 27.587 +/- 0.008 A, V = 5275.5 +/- 0.2 A3, Z = 4, dm = 1.152 +/- 0.005 g cm-3, dcal = 1.150 +/- 0.005 g cm-3. The overall residual factor R = 0.084 for 2342 reflections, with 2 theta max = 140 degrees using CuK alpha radiation. The backbone torsion angles are theta 1 = -171(1) degrees, omega 0 = 168(1) degrees, phi 1 = 77(2) degrees, psi 1 = 41(2) degrees, omega 1 = 169(1) degrees, phi 2 = -46(2) degrees, psi 2 = -24(2) degrees, omega 2 = 179(1) degrees, phi 3 = -63(2) degrees, psi 3 = 19(2) degrees, omega 3 = 171(1) degrees, phi 4 = -67(2) degrees, psi 4 = -8(1) degrees, omega 4 = 169(1) degrees, phi 5 = -61(1) degrees, psi 5 = -26(1) degrees, omega 5 = 177(1) degrees, phi 6 = -122(1) degrees, psi 6T = 26(2) degrees. The peptide adopts a 3(10)-helical conformation with three intramolecular hydrogen bonds (i + 3-->i) involving carbonyl oxygen atoms of Phe1, dehydro-Phe2, Val3, and the NH groups of Phe4, dehydro-Phe5, and Val6 with distances of 3.01(1), 2.82(1), and 3.09(2) A, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)