Two diastereoisomers of cyclo(Pro-Tyr) have been synthesized simultaneously. The crystal structures and conformations of both cyclo($\smallL}$-Pro-$\smallL}$-Tyr) and a racemic mixture of cyclo($\smallD}$-Pro-$\smallL}$-Tyr) and cyclo($\smallL}$-Pro-$\smallD}$-Tyr), abbreviated as rac-cyclo($\smallD}$-Pro-$\smallL}$-Tyr/$\smallL}$-Pro-$\smallD}$-Tyr), have been determined by a single-crystal X-ray diffraction study at low temperature. The crystals of rac-cyclo($\smallD}$-Pro-$\smallL}$-Tyr/$\smallL}$-Pro-$\smallD}$-Tyr) belong to orthorhombic space group $Pna2_1$ with a = 10.755 (1), b = 12.699 (1), c = 9.600 (1) $\AA}$ and Z = 4. The tyrosine side chain is folded towards the diketopiperazine (DKP) ring. The DKP ring adopts a twist boat conformation with pseudo symmetry $C_2v}$. The pyrrolidine ring has an envelope conformation with the N5, C4, C7 and C8 atoms in a plane. The crystal of rac-cyclo($\smallD}$-Pro-$\smallL}$-Tyr/$\smallL}$-Pro-$\smallD}$-Tyr) is stabilized by hydrogen bonds between amide N2-H2 and carbonyl oxygen O2 in the neighbor. The hydroxyl group of tyrosine residue is also hydrogen bonded to the oxygen of the carbonyl group of the DKP ring in the next molecule. The spectroscopic properties of both isomers are also described.
我们同时合成了环(Pro-Tyr)的两种非对映异构体。环(
$\smallL}$- Pro-
$\smallL}$-Tyr)和环(
$\smallD}$-Pro-
$\smallL}$-Tyr)的外消旋混合物、简称 rac-cyclo(
$\smallD}$-Pro-
$\smallL}$-Tyr/
$\smallL}$-Pro-
$\smallD}$-Tyr),是在低温下通过单晶 X 射线衍射研究确定的。rac-cyclo(
$\smallD}$-Pro-
$\smallL}$-Tyr/
$\smallL}$-Pro-
$\smallD}$-Tyr) 晶体属于正交空间群
$Pna2_1$ ,a = 10.755 (1),b = 12.699 (1),c = 9.600 (1)
$\AA}$,Z = 4。
酪氨酸侧链向二酮
哌嗪(DKP)环折叠。DKP 环采用假对称性
$C_2v}$的扭曲船形构象。
吡咯烷环具有包络构象,N5、C4、C7 和 C8 原子在一个平面上。rac-cyclo(
$\smallD}$-Pro-
$\smallL}$-Tyr/
$\smallL}$-Pro-
$\smallD}$-Tyr)的晶体通过邻位的酰胺 N2-H2 和羰基氧 O2 之间的氢键而稳定。
酪氨酸残基的羟基也与下一个分子中 DKP 环的羰基氧氢键结合。此外,还介绍了这两种异构体的光谱特性。