Cinchona alkaloid derivatives as Brønsted base catalysts have attracted considerable attention in the field of asymmetric catalysis. However, their potential application as chiral solvating agents has not been described. In this research, we investigated the use of the Cinchona alkaloid dimer, namely, (DHQ)₂PHAL, as a chiral solvating agent for discerning various mandelic acid derivatives through ¹H NMR spectroscopy. The addition of catalytic amounts of DMAP facilitated this process. Our experimental results demonstrate that dimeric (DHQ)₂PHAL exhibits remarkable chiral discrimination properties regarding the diagnostic split protons of ¹H NMR signals (including 24 examples, up to 0.321 ppm). Furthermore, it serves as an excellent chiral discriminating agent and provides good resolution for racemic chiral phosphoric acid as determined by ³¹P NMR spectroscopy. The quality of enantiodifferentiation has also been evaluated by means of the parameter “resolution (R_s)”. Significantly, this class of CSAs based on (alkaloid)₂linker systems with an azaaromatic linker can be directly employed, which is commercially available in an enantiopure form at very low cost and exhibits promising potential in determining the enantiopurity of α-hydroxy acids by chemoselective and biocatalytic reactions.

中文翻译：

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使用金鸡纳生物碱二聚体作为手性溶剂对羧酸进行对映特异性分析


金鸡纳生物碱衍生物作为布朗斯台德碱催化剂在不对称催化领域引起了广泛关注。然而，它们作为手性溶剂化剂的潜在应用尚未被描述。在本研究中，我们研究了金鸡纳生物碱二聚体，即 (DHQ) ₂ PHAL 作为手性溶剂化剂，通过 ¹ H NMR 光谱辨别各种扁桃酸衍生物。添加催化量的 DMAP 促进了这一过程。我们的实验结果表明，二聚体 (DHQ) ₂ PHAL 在 ¹ H NMR 信号（包括 24 个示例，高达 0.321 ppm）的诊断分裂质子方面表现出显着的手性辨别特性。此外，它还可以作为优异的手性鉴别剂，并为通过 ³¹ P NMR 光谱测定的外消旋手性磷酸提供良好的分辨率。对映体分化的质量也通过参数“分辨率(R _s )”进行了评估。值得注意的是，这类基于（生物碱） ₂ 连接体系统和氮杂芳香族连接体的CSA可以直接使用，它可以以对映体纯形式以非常低的成本在商业上获得，并且在测定对映体纯度方面表现出良好的潜力。通过化学选择性和生物催化反应生成α-羟基酸。