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手性是自然界和生命体中普遍存在的现象, 是微观小分子和宏观物质的一种基本属性。在现实生活中，越来越多的药物和材料通过控制手性来提高药物和材料性能。因此手性的研究一直是科学界，尤其是生物医药和光学材料界最热门的课题之一。 化学中小分子手性的研究为两类：发现新手性和控制手性新方法。半个多世纪以来，多位化学家因控制手性方法学的工作被授予诺贝尔化学奖。有趣的是，几乎没有文章报道过关于新手性的发现方面的工作。迄今为止，已经发现的主要分子手性类型有：中心手性、轴手性、螺环手性、刚性面手性（如二茂铁，螺烯手性）和柔性面手性（如折叠手性）。 近两年来，南京大学/美国德州理工大学李桂根团队建立了一种新型手性-向标手性 (Orientational Chirality)：即一个手性中心可以产生三对对映体和六对非对映异构体。该手性特点是有C(sp)-C(sp3)或C(sp2)-C(sp3)轴链接的手性中心和一个远程固定阻断官能团。最近，李桂根与湖南科技大学焦银春教授团队合作设计并合成了一系列新型的向标手性分子。该类设计利用非手性氰基作为远程阻断官能团，同时利用非手性氨基保护基团 (tBuSO2-) 连接在底物上。向标手性的构型完全被碳手性中心控制。通过X-射线衍射分析确定了它们的绝对构型：最稳定的向标手性异构体为NHTs远离氰基, 而不是两个芳香取代基远离氰基。
图 1. 向标手性异构体晶体结构 图 2. 三种可能的向标手性异构体 值得一提的是，向标手性异构体与传统的沿C(sp2)-C(sp3)轴旋转时存在六个能垒的Felkin-Ahn-type 或 Cram-type模型有本质区别。在向标手性模型中，通过旋转操作仅产生三个旋转势垒。向标手性可以使得一个手性中心能够产生出六种异构体，而不是传统意义上的两种异构体。这为手性药物和手性材料的发展提供了更加广阔的空间和可能性。 图 3. 传统的Felkin-Ahn and 向标手性模型 同时，对三种向标手性异构体的相对能量进行了计算。计算结果进一步证实，酰胺保护的氨基远离左轴的异构体，是最稳定的异构体。另外两种向标手性异构体的能量， 分别升高0.5kcal/mol 和2.2 kcal/mol。 图4. 向标手性异构体及其相对能量 综上所述，该项工作发展了新的向标手性，将会在化学、物理学、生物学、农药、制药和医学以及材料科学方面产生广泛的影响。向标手性的潜在应用包括但不限于手性配体/催化剂、新型氨基酸/多肽、用于捕光的纳米材料和生物混合系统、手性传感器、自旋选择性激子输运、光学领域的芯片级光学元件、量子信息及其存储等方面。 论文信息 Design and Asymmetric Control of Orientational Chirality by Using the Combination of C(sp2)-C(sp) Levers and Achiral N-Protecting Group Yu Wang, Ting Xu, Shengzhou Jin, Jia-Yin Wang, Qingkai Yuan, Hao Liu, Yao Tang, Sai Zhang, Wenxin Yan, Yinchun Jiao, Guigen Li Chemistry – A European Journal DOI: 10.1002/chem.202400005
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