Thiazinoquinones as New Promising Multistage Schistosomicidal Compounds Impacting Schistosoma mansoni and Egg Viability

Schistosomiasis is the most significant neglected tropical parasitic disease caused by helminths in terms of morbidity and mortality caused by helminths. In this work, we present the antischistosomal activity against Schistosoma mansoni of a rationally selected small set of thiazinoquinone derivatives, some of which were previously found to be active against Plasmodium falciparum and others synthesized ad hoc. The effects on larvae, juvenile, and adult parasite viability as well as on egg production and development were investigated, resulting in the identification of new multistage antischistosomal hit compounds. The most promising compounds 6, 8, 13, and 14 with a LC₅₀ value on schistosomula from ∼5 to ∼15 μM also induced complete death of juvenile (28 days old) and adult worm pairs (7 weeks old) and a detrimental effect on egg production and development in vitro. Structure-activity relationships (SARs) were analyzed by means of computational studies leading to the hypothesis of a redox-based mechanism of action with a one-electron reduction bioactivation step and the subsequent formation of a toxic semiquinone species, similarly to what was previously observed for the antiplasmodial activity. Our results also evidenced that the selective toxicity against mammalian cells or parasites as well as specific developmental stages of a parasite can be addressed by varying the nature of the introduced substituents.

Syntheses of benzophenone-xanthone hybrid polyketides and their antibacterial activities

Muchimangins are benzophenone-xanthone hybrid polyketides produced by Securidaca longepedunculata. However, their biological activities have not been fully investigated, since they are minor constituents in this plant. To evaluate the possibility of muchimangins as antibacterial agent candidates, five muchimangin analogs were synthesized from 2,4,5-trimethoxydiphenyl methanol and the corresponding xanthones, by utilizing p-toluenesulfonic acid monohydrate for the Brønsted acid-catalysis. The antibacterial assays against Gram-positive bacteria, Staphylococcus aureus and Bacillus subtilis, and Gram-negative bacteria, Klebsiella pneumoniae and Escherichia coli, revealed that the muchimangin analogs (±)-1,3,6,8-tetrahydroxy-4-(phenyl-(2',4',5'-trimethoxyphenyl)methyl)-xanthone (1), (±)-1,3,6-trihydroxy-4-(phenyl-(2',4',5'-trimethoxyphenyl)methyl)-xanthone (2), and (±)-1,3-dihydroxy-4-(phenyl-(2',4',5'-trimethoxyphenyl)methyl)-xanthone (3) showed significant activities against S. aureus, with MIC values of 10.0, 10.0, and 25.0μM, respectively. Analogs (±)-1 and (±)-2 also exhibited antibacterial activities against B. subtilis, with MIC values of 50.0 and 12.5μM, respectively. Furthermore, (+)-3 enhanced the antibacterial activity against S. aureus, with a MIC value of 10μM.

Angiotensin II pseudopeptides containing 1,3,5-trisubstituted benzene scaffolds with high AT2 receptor affinity

Two 1,3,5-trisubstituted aromatic scaffolds intended to serve as gamma-turn mimetics have been synthesized and incorporated in five pseudopeptide analogues of angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe), replacing Val-Tyr-Ile, Val-Tyr, or Tyr-Ile. All the tested compounds exhibited nanomolar affinity for the AT2 receptor with the best compound (3) having a K(i) of 1.85 nM. Four pseudopeptides were AT2 selective, while one (5) also exhibited good affinity for the AT1 receptor (K(i) = 30.3 nM). This pseudopeptide exerted full agonistic activity in an AT2 receptor induced neurite outgrowth assay but displayed no agonistic effect in an AT1 receptor functional assay. Molecular modeling, using the program DISCOtech, showed that the high-affinity ligands could interact similarly with the AT2 receptor as other ligands with high affinity for this receptor. A tentative agonist model is proposed for AT2 receptor activation by angiotensin II analogues. We conclude that the 1,3,5-trisubstituted benzene rings can be conveniently prepared and are suitable as gamma-turn mimics.