Tarnowska M, Oldziej S, Liwo A, Kania P, Kasprzykowski F, Grzonka Z
Department of Chemistry, University of Gdańsk, Poland.
Eur Biophys J. 1992;21(3):217-22. doi: 10.1007/BF00196766.
Diazomethyl ketones are one of the most effective irreversible inhibitors of cysteine proteinases and are therefore very important in drug design. In the present study a mechanism of inactivation is proposed based on the results of model MNDO calculations of the possible pathways. It was found that the mercaptide nucleophile, on approaching the carbonyl carbon as in the catalytic reaction path, binds to the inner diazo nitrogen. The intermediate thus formed can rearrange giving a stable product, beta-thioketone, and molecular nitrogen, with a considerable energy gain. The energy barrier to this process is equal to 36.9 kcal/mol, and corresponds to a pyramidal transition state with the vertex at the methylene carbon and the base formed by the carbonyl, thiol, and diazo groups. The energy barrier can be lowered on deprotonation of the intermediate. Based on the results obtained it was concluded that good irreversible inhibitors of cysteine proteases must fulfil two structural requirements: i) the dimensions and charge distribution must be similar to those of the peptide bond and ii) a second electrophilic center must be present in the neighbourhood of the carbonyl carbon. These are requirements which are satisfied by other strong cysteine proteinase inhibitors: beta-chloroketones and beta-ketooxiranes.
重氮甲基酮是半胱氨酸蛋白酶最有效的不可逆抑制剂之一，因此在药物设计中非常重要。在本研究中，基于对可能途径的模型MNDO计算结果，提出了一种失活机制。研究发现，硫醇盐亲核试剂在催化反应路径中接近羰基碳时，会与内部重氮氮结合。由此形成的中间体可以重排，生成稳定产物β-硫酮和分子氮，并伴有相当大的能量增益。该过程的能垒等于36.9千卡/摩尔，对应于一个锥形过渡态，其顶点位于亚甲基碳上，底面由羰基、硫醇和重氮基团形成。中间体去质子化后，能垒会降低。根据所得结果得出结论，良好的半胱氨酸蛋白酶不可逆抑制剂必须满足两个结构要求：i）尺寸和电荷分布必须与肽键相似；ii）羰基碳附近必须存在第二个亲电中心。其他强半胱氨酸蛋白酶抑制剂：β-氯酮和β-酮环氧乙烷也满足这些要求。
