4‑Benzoylamino-3-hydroxybutyric Acid, Historically First “Anomalous Racemate”: Reinvestigation

Chiral 4-benzoylamino-3-hydroxybutyric acid (1) was recognized in 1930 as the first example of “anomalous racemates” (correct to say, anomalous conglomerates), that is, specific addition compounds formed by different enantiomers in unequal ratio. Through the comparative (racemic against homochiral samples) inspection of the IR spectra, single crystal X-ray diffraction, PXRD analysis, and solubility data we have found that this substance forms normal racemic compound in the solid state, and must be excluded from the very short list of anomalous conglomerates. At the same time homo-1 is dissolved in 25 times better than rac-1, and this feature belongs to another interesting and rare type, namely, “anticonglomerates”. Some of the reasons for this behavior are discussed.

手性4-苯甲酰氨基-3-羟基丁酸(1)于1930年被认定为"异常外消旋体"（准确而言应为异常聚集体）的首个实例，即由不同对映体以不等比例形成的特定加合物。研究团队通过对比外消旋样品与同手性样品的红外（IR）光谱、单晶X射线衍射、粉末X射线衍射（PXRD）分析结果及溶解度数据，发现该物质在固态下仅能形成普通外消旋化合物，因此应将其从极短的异常聚集体候选名录中剔除。与此同时，同手性形式的该化合物（homo-1）的溶解度是外消旋形式（rac-1）的25倍，这一特性属于另一种罕见且极具研究价值的类型，即"反聚集体"。本文还对引发该现象的部分原因进行了探讨。