NMR conformational analysis in solution of a potent class of cysteine proteases inhibitors
作者:Archimede Rotondo、Roberta Ettari、Silvana Grasso、Maria Zappalà
DOI:10.1007/s11224-015-0597-5
日期:2015.8
Conformational analysis of a potent class of cysteine protease inhibitors is thoroughly studied by NMR, in both, polar and apolar solvents to get a better insight over the known biological activity and migration through biological media. These molecules are composed by a benzodiazepine (BDZ) scaffold connected to a bromo-isoxazoline (IOX) ring through an alkyl spacer (AS) with up to four-carbon atoms. Data, supported by theoretical calculations at DFT level, reveal that both BDZ and IOX keep a pretty rigid and asymmetric conformation, so that four diastereo-atropisomers (two mirror-image couples) are generated. The relative stiffness of these substrates, maintained also in different solvents, is confirmed by: (a) remarkable separation of diastereotopic protons; (b) specific “through the space contacts” (NOESY); and (c) very good fitting of the coupling constants evaluations. The prototypic compound with the longer AS shows two main conformations and a certain dynamic freedom around the AS torsional angles close to IOX; according to our data, the AS length is not fundamental for the functional BDZ and IOX fitting into the macromolecular complex; however, it does play a crucial role to cross the parasite cell membranes.
我们通过核磁共振对一类强效半胱氨酸蛋白酶抑制剂在极性和非极性溶剂中的构象分析进行了深入研究,以便更好地了解其已知的生物活性以及在生物介质中的迁移情况。这些分子由一个苯并二氮杂卓(BDZ)支架和一个溴异噁唑啉(IOX)环组成,并通过一个最多有四个碳原子的烷基间隔物(AS)连接起来。在 DFT 水平的理论计算支持下,数据显示 BDZ 和 IOX 都保持着相当刚性和不对称的构象,因此产生了四种非对映异构体(两个镜像对偶)。这些底物的相对刚性在不同溶剂中也保持不变,这一点通过以下方面得到了证实:(a) 非对映质子的显著分离;(b) 特定的 "空间接触"(NOESY);(c) 偶联常数评估的良好拟合。具有较长 AS 的原型化合物显示出两种主要构象,并且在靠近 IOX 的 AS 扭角周围具有一定的动态自由度;根据我们的数据,AS 长度对于功能性 BDZ 和 IOX 与大分子复合物的配合并不重要;但是,它对于穿过寄生虫细胞膜确实起着至关重要的作用。