The belactosin A analog 2a, having the unnatural cis-cyclopropane structure instead of the trans-cyclopropane structure in belactosin A, is a much more potent proteasome inhibitor than belactosin A. However, its cell growth inhibitory effect is rather lower than that expected from its remarkable proteasome inhibitory effect, probably due to its instability under cellular conditions. We hypothesized that the instability of 2a was due to chemical and enzymatic hydrolysis of the strained β-lactone moiety. Thus, to increase the stability of 2a by chemical modification, its analogs with a sterically more hindered β-lactone moiety and/or cyclopropylic strain-based conformational restriction were designed and synthesized, resulting in the identification of a stabilized analog 6a as a proteasome inhibitor with cell growth inhibitory effects. Our findings suggest that the chemical and biological stability of 2a is significantly affected by the steric hindrance around its β-lactone carbonyl moiety and the conformational flexibility of the molecule.
                                    具有非天然顺式
环丙烷结构的贝拉可素A类似物2a,其作为
蛋白酶体
抑制剂的效力远超具有反式
环丙烷结构的贝拉可素A。然而,其抑制细胞生长的效果却远低于从其显著的
蛋白酶体抑制效果中所预期的
水平,这可能归因于其在细胞环境下的不稳定性。我们假设2a的不稳定性源于其受压的β-内酯环的
化学和酶促
水解。因此,为了通过
化学修饰增强2a的稳定性,我们设计并合成了具有空间位阻更大的β-内酯环和/或基于
环丙烷张力的构象限制的类似物,从而鉴定出稳定化的类似物6a,它是一种具有细胞生长抑制效应的
蛋白酶体
抑制剂。我们的发现表明,2a的
化学和
生物稳定性显著受到其β-内酯羰基周围空间位阻和分子构象灵活性的影响。