作者:Yael Gozin、Donald Hilvert
DOI:10.1002/hlca.200290015
日期:2002.12
normal electron-demand Diels–Alder reactions between NEM and unsubstituted thiophene dioxide or 2,3,4,5-tetramethylthiophene dioxide, which are much smaller or nearly isosteric with TCTD, respectively, are not detectably accelerated. These results show that the electronic properties of the 1E9 active site are optimized to a remarkable degree for the inverse electron-demand Diels–Alder reaction for which
一系列取代的噻吩二氧化物的测试作为用于抗体1E9,其用一个hexachloronorbornene衍生物引起二烯基片,通常催化逆电子需求狄尔斯-阿尔德-2,3,4,5- tetrachlorothiophene氧化钛(TCTD)和之间的反应N-乙基马来酰亚胺(NEM)。先前的结构和计算研究表明,该系统的催化效率部分源于非极性活性位点与该反应的过渡态之间的紧密结合。然而,用Br原子代替半抗原中的所有Cl原子不会导致亲和力的损失(K d= 0.1nM),表明在结合口袋内的残基中具有显着的构象柔韧性。与该观察结果一致,尽管2,3,4,5-四溴噻吩二氧化物比TCTD大得多,但却是抗体的良好底物(k cat = 1.8 min -1,K NEM = 14μM)。相比之下,在NEM和未取代的噻吩二氧化物或2,3,4,5-四甲基噻吩二氧化物之间的正常电子需求Diels-Alder反应,分别与TCTD相比