Development of Novel Peptide-Based Michael Acceptors Targeting Rhodesain and Falcipain‑2 for the Treatment of Neglected Tropical Diseases (NTDs)

This paper describes the development of a class of peptide-based inhibitors as novel antitrypanosomal and antimalarial agents. The inhibitors are based on a characteristic peptide sequence for the inhibition of the cysteine proteases rhodesain of Trypanosoma brucei rhodesiense and falcipain-2 of Plasmodium falciparum. We exploited the reactivity of novel unsaturated electrophilic functions such as vinyl-sulfones, -ketones, -esters, and -nitriles. The Michael acceptors inhibited both rhodesain and falcipain-2, at nanomolar and micromolar levels, respectively. In particular, the vinyl ketone 3b has emerged as a potent rhodesain inhibitor (k2nd = 67 × 106 M–1 min–1), endowed with a picomolar binding affinity (Ki = 38 pM), coupled with a single-digit micromolar activity against Trypanosoma brucei brucei (EC50 = 2.97 μM), thus being considered as a novel lead compound for the discovery of novel effective antitrypanosomal agents.本研究阐述了一类基于肽段的抑制剂的开发过程，这类抑制剂可作为新型抗锥虫与抗疟药物。该类抑制剂以特征性肽序列为基础，可靶向抑制罗得西亚锥虫（Trypanosoma brucei rhodesiense）的半胱氨酸蛋白酶罗得西亚蛋白酶（rhodesain），以及恶性疟原虫（Plasmodium falciparum）的镰状疟原虫半胱氨酸蛋白酶2（falcipain-2）。本研究利用了新型不饱和亲电官能团的反应活性，例如乙烯基砜、乙烯基酮、乙烯基酯及乙烯基腈。这类迈克尔受体（Michael acceptors）对罗得西亚蛋白酶与镰状疟原虫半胱氨酸蛋白酶2均具有抑制活性，其抑制活性分别处于纳摩尔与微摩尔级别。尤为值得关注的是，乙烯基酮3b已被证实为一款强效的罗得西亚蛋白酶抑制剂，其二级速率常数（k2nd）可达67×10⁶ M⁻¹·min⁻¹，结合亲和力处于皮摩尔级别（抑制常数Ki=38 pM），同时对布氏锥虫布氏亚种（Trypanosoma brucei brucei）展现出个位数微摩尔级的抗虫活性（半数效应浓度EC50=2.97 μM），因此可被视为开发新型高效抗锥虫药物的潜在先导化合物。