Human leukocyte elastase (HLE) is a serine protease stored in and secreted from neutrophils that plays a determinant role in the pathogenesis of several lung diseases. 4-Oxo-beta-lactams, previously reported as acylating agents of porcine pancreatic elastase, were found to be selective and potent inhibitors of HLE. Structure-activity relationship analysis showed that inhibitory activity is very sensitive to the nature of C-3 substituents, with small alkyl substituents such as a gem-diethyl group improving the inhibitory potency when compared to gem-methyl benzyl or ethyl benzyl counterparts. 4-Oxo-beta-lactams containing a heteroarylthiomethyl group on the para position of an N(1)-aryl moiety afforded highly potent and selective inhibition of HLE, even at a very low inhibitor to enzyme ratio, as shown by the k(on) value of 3.24 x 10(6) M(-1) s(-1) for 6f. The corresponding ortho isomers were 40- to 90-fold less potent.

A series of artemisinin-vinyl sulfone hybrid molecules with the potential to act in the parasite food vacuole via endoperoxide activation and falcipain inhibition was synthesized and screened for antiplasmodial activity and falcipain-2 inhibition. All conjugates were active against the Plasmodium falciparum W2 strain in the low nanomolar range and those containing the Leu-hPhe core inhibited falcipain-2 in low micromolar range. Keywordsantimalarial; artemisinin; FP-2; Vinylsulfone Artemisinin, 1, a sesquiterpene lactone isolated from the Artemisia annua Chinese herb, and its analogues (e.g. artemether, 2, arteether, 3, and artesunate, 4) were a major breakthrough in malaria chemotherapy because they produce a very rapid therapeutic response, particularly against multidrug-resistant Plasmodium falciparum malaria. 1,2 Despite the rapid clearance of parasites, the short half-lives of these compounds lead to many late recrudescences after monotherapy. 3 Thus, artemisinin-based combination therapy (ACT) has now been recommended by the World Health Organisation as standard therapy for falciparum malaria. 4 Cysteine proteases from malaria parasites are of particular interest as therapeutic targets due to their role in parasite development. 5 P. falciparum expresses four cysteine proteases from the papain family known as falcipains, of which falcipain-2 (FP-2) 6,7 and falcipain-3 (FP-3) 7,8 are the most relevant as therapeutic targets. Peptidyl vinyl sulfones, e.g. 5, are potent irreversible inhibitors of falcipains, acting as Michael acceptors of the catalytic cysteine residue. 9 Falcipain inhibitors have been shown to inhibit the development of cultured erythrocytic parasites by blocking the hydrolysis of host hemoglobin and to cure mice infected with lethal malaria infections. 10 *Corresponding authors: Phone: +351217946476; Fax: +35 1217946470; fclopes@ff.ul.pt. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptA concern regarding the use of protease inhibitors as antimalarials is that selection of drugresistant mutants will eventually occur. Indeed, parasites resistant to a dipeptidyl vinyl sulfone have been selected in the laboratory, although this resistance was somewhat unstable. 11 Thus, dipeptidyl vinyl sulfones are obvious candidates for combination antimalarial therapy as a strategy to retard the development of resistance. This information prompted us to design artemisinin-vinyl sulfone hybrid molecules with the potential to help prevent multi-drug resistance in P. falci...

In a search for effective compounds against both the blood-and liver-stages of infection by malaria parasites with the ability to block the transmission of the disease to mosquito vectors, a series of hybrid compounds combining either a 1,2,4-trioxane or 1,2,4,5-tetraoxane and 8-aminoquinoline moieties were synthesized and screened for their antimalarial activity. These hybrid compounds showed high potency against both exoerythrocytic and erythrocytic forms of malaria parasites, comparable to representative trioxanebased counterparts. Furthermore, they efficiently blocked the development of the sporogonic cycle in the mosquito vector. The tetraoxane-based hybrid 5, containing an amide linker between the two moieties, effectively cleared a patent blood-stage P. berghei infection in mice after i.p. administration. Overall, these results indicate that peroxide-8-aminoquinoline hybrids are excellent starting points to develop an agent that conveys all the desired antimalarial multistage activities in a single chemical entity and, as such, with the potential to be used in malaria elimination campaigns.

The use of artemisinin or other endoperoxides in combination with other drugs is a strategy to prevent development of resistant strains of Plasmodium parasites. Our previous work demonstrated that hybrid compounds, comprising endoperoxides and vinyl sulfones, were capable of high activity profiles comparable to artemisinin and chloroquine while acting through two distinct mechanisms of action: oxidative stress and falcipain inhibition. In this study, we adapted this approach to a novel class of falcipain inhibitors: peptidomimetic pyrimidine nitriles. Pyrimidine tetraoxane hybrids displayed potent nanomolar activity against three strains of Plasmodium falciparum and falcipain-2, combined with low cytotoxicity. In vivo, a decrease in parasitemia and an increase in survival of mice infected with Plasmodium berghei was observed when compared to control. All tested compounds combined good blood stage activity with significant effects on liver stage parasitemia, a most welcome feature for any new class of antimalarial drug.

The emergence of artemisinin-resistant Plasmodium falciparum malaria in Southeast Asia has reinforced the urgent need to discover novel chemotherapeutic strategies to treat and control malaria. To address this problem, we prepared a set of dual-acting tetraoxane-based hybrid molecules designed to deliver a falcipain-2 (FP-2) inhibitor upon activation by iron(II) in the parasite digestive vacuole. These hybrids are active in the low nanomolar range against chloroquine-sensitive and chloroquine-resistant P. falciparum strains. We also demonstrate that in the presence of FeBr₂ or within infected red blood cells, these molecules fragment to release falcipain inhibitors with nanomolar protease inhibitory activity. Molecular docking studies were performed to better understand the molecular interactions established between the tetraoxane-based hybrids and the cysteine protease binding pocket residues. Our results further indicate that the intrinsic activity of the tetraoxane partner compound can be masked, suggesting that a tetraoxane-based delivery system offers the potential to attenuate the off-target effects of known drugs.

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