Karle I L
Int J Pept Protein Res. 1986 Oct;28(4):420-7. doi: 10.1111/j.1399-3011.1986.tb03274.x.
All the peptide bonds in cyclic(Gly-L-Pro-D-Phe-Gly-L-Ala) are in the trans conformation; however, the peptide bond C'5-N1 is twisted by 19 degrees from planarity (omega 5 = -161 degrees). A Type II beta-turn encompasses the L-Pro-D-Phe residues. Carbonyl oxygens O2, O4 and O5 are directed to the same side of the average plane through the backbone ring and they form hydrogen bonds with N3, N5 and N1, respectively, in adjacent molecules in a stacked column where the adjacent molecules are related by one translational unit. The conformation of the backbone is different from that established in other molecules with the DLDDL chirality sequence. The P21 cell contains two molecules of C21H26N5O5 with a = 4.836(2) A, b = 18.346(8) A, c = 12.464(5) A and beta = 100.05(4) degrees. The R factor for 1382 data with [F0[ greater than 1 sigma is 7.0%.
环（甘氨酸 - 脯氨酸 - D - 苯丙氨酸 - 甘氨酸 - L - 丙氨酸）中的所有肽键均处于反式构象；然而，肽键C'5 - N1相对于平面扭转了19度（ω5 = -161度）。一个II型β-转角包含L - 脯氨酸 - D - 苯丙氨酸残基。羰基氧O2、O4和O5通过主链环指向平均平面的同一侧，并且它们分别与堆叠柱中相邻分子中的N3、N5和N1形成氢键，相邻分子通过一个平移单元相关联。主链的构象与具有DLDDL手性序列的其他分子中确立的构象不同。P21晶胞包含两个C21H26N5O5分子，a = 4.836(2) Å，b = 18.346(8) Å，c = 12.464(5) Å，β = 100.05(4)度。对于1382个[F0]大于1σ的数据，R因子为7.0%。
