Dalhus B, Gorbitz C H
Department of Chemistry, University of Oslo, PO Box 1033, Blindern, N-0315 Oslo, Norway.
Acta Crystallogr B. 2000 Aug;56(Pt 4):720-7. doi: 10.1107/s0108768100002810.
A reinvestigation of the crystal structure of the 1:1 mixture of the two racemates DL-isoleucine and DL-allo-isoleucine, with a detailed analysis of interatomic distances between alternative side-chain positions, reveals a systematic distribution of the four stereoisomers in this crystal. Two different molecular chains exist in the crystal and each such chain accommodates a single diastereomeric pair only (L-isoleucine:D-allo-isoleucine or D-isoleucine:L-allo-isoleucine). The crystal is built up by a stacking of such chains in two dimensions and three different packing modes for the two types of chains are discussed. Crystallization experiments of the two individual racemates in the 1:1 mixture of DL-isoleucine:DL-allo-isoleucine have been undertaken. The structure of the racemate DL-isoleucine is presented. The molecular arrangements in this racemate and the 1:1 DL-isoleucine:DL-allo-isoleucine mixture are closely related. Furthermore, the spontaneous resolution of enantiomers upon crystallization of the other racemate, DL-allo-isoleucine, is rationalized on the basis of the aforementioned analysis of interatomic distances in the 1:1 DL-isoleucine:DL-allo-isoleucine complex. Structural data for a new L-isoleucine: D-allo-isoleucine complex are also given.
对两种外消旋体DL-异亮氨酸和DL-别异亮氨酸1:1混合物的晶体结构进行重新研究，并对替代侧链位置之间的原子间距离进行详细分析，揭示了这四种立体异构体在该晶体中的系统分布。晶体中存在两条不同的分子链，每条这样的链仅容纳一对非对映异构体（L-异亮氨酸:D-别异亮氨酸或D-异亮氨酸:L-别异亮氨酸）。该晶体是由这些链在二维空间中堆积而成的，并讨论了两种类型链的三种不同堆积模式。已对DL-异亮氨酸:DL-别异亮氨酸1:1混合物中两种单独外消旋体进行了结晶实验。给出了外消旋体DL-异亮氨酸的结构。该外消旋体和1:1 DL-异亮氨酸:DL-别异亮氨酸混合物中的分子排列密切相关。此外，根据上述对1:1 DL-异亮氨酸:DL-别异亮氨酸复合物中原子间距离的分析，解释了另一种外消旋体DL-别异亮氨酸结晶时对映体的自发拆分。还给出了一种新的L-异亮氨酸:D-别异亮氨酸复合物的结构数据。
