Development of Novel Benzodiazepine-Based Peptidomimetics as Inhibitors of Rhodesain from Trypanosoma brucei rhodesiense

Starting from the reversible rhodesain inhibitors 1 a–c, which have Ki values towards the target protease in the low-micromolar range, we have designed a series of peptidomimetics, 2 a–g, that contain a benzodiazepine scaffold as a β-turn mimetic; they are characterized by a specific peptide sequence for the inhibition of rhodesain. Considering that irreversible inhibition is strongly desirable in the case of a parasitic target, a vinyl ester moiety acting as Michael-acceptor was introduced as the warhead; this portion was functionalized in order to evaluate the size of corresponding enzyme pocket that could accommodate this substituent. With this investigation, we identified an irreversible rhodesain inhibitor (i. e., 2 g) with a k2nd value of 90 000 M⁻¹ min⁻¹ that showed antitrypanosomal activity in the low-micromolar range (EC₅₀=1.25 μM), this may be considered a promising lead compound in the drug-discovery process for treating human African trypanosomiasis (HAT).