Understanding the mechanism of the chiral phosphoric acid-catalyzed aza-Cope rearrangement.

The first catalytic enantioselective aza-Cope rearrangement was reported in 2008 by Rueping et al. The reaction is catalyzed by a 1,1'-bi-2-naphthol-derived (BINOL-derived) phosphoric acid and achieved high yields and enantioselectivities (up to 97 : 3 er with 75% yield). This work utilizes Density Functional Theory to understand the mechanism of the reaction and explain the origins of the enantioselectivity. An extensive conformational search was carried out to explore the different activation modes by the catalyst and, the Transition State (TS) leading to the major product was found to be 1.3 kcal mol-1 lower in energy than the TS leading to the minor product. The origin of this stabilization was rationalized with NBO and NCI analysis: it was found that the major TS has a greater number of non-bonding interactions between the substrate and the catalyst, and shows stronger H-bond interactions between H atoms in the substrate and the O atoms in the phosphate group of the catalyst.

Synthesis and biological evaluation of 1-alkylaminomethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii.

As an extension of our project aimed at the search for new chemotherapeutic agents against Chagas disease and toxoplasmosis, several 1,1-bisphosphonates were designed, synthesized and biologically evaluated against Trypanosoma cruzi and Toxoplasma gondii, the etiologic agents of these diseases, respectively. In particular, and based on the antiparasitic activity exhibited by 2-alkylaminoethyl-1,1-bisphosphonates targeting farnesyl diphosphate synthase, a series of linear 2-alkylaminomethyl-1,1-bisphosphonic acids (compounds 21-33), that is, the position of the amino group was one carbon closer to the gem-phosphonate moiety, were evaluated as growth inhibitors against the clinically more relevant dividing form (amastigotes) of T. cruzi. Although all of these compounds resulted to be devoid of antiparasitic activity, these results were valuable for a rigorous SAR study. In addition, unexpectedly, the synthetic designed 2-cycloalkylaminoethyl-1,1-bisphosphonic acids 47-49 were free of antiparasitic activity. Moreover, long chain sulfur-containing 1,1-bisphosphonic acids, such as compounds 54-56, 59, turned out to be nanomolar growth inhibitors of tachyzoites of T. gondii. As many bisphosphonate-containing molecules are FDA-approved drugs for the treatment of bone resorption disorders, their potential nontoxicity makes them good candidates to control American trypanosomiasis and toxoplasmosis.

Mechanistic Insights into a Chiral Phosphoric Acid-Catalyzed Asymmetric Pinacol Rearrangement.

The first catalytic enantioselective pinacol rearrangement was reported by Antilla and co-workers in 2010. The reaction was catalyzed by a chiral phosphoric acid and resulted in high levels of enantioselectivity (up to 96% ee). The present study uses density functional theory to investigate the mechanism and origins of stereoselectivity of this important reaction and to explain the difference in selectivity between different catalysts. An OH···O hydrogen bond between the intermediate indolyl alcohol and the phosphate group from the catalyst together with a CH···O hydrogen bond between the indole and the phosphate group were observed in the preferred activation mode for the stereodetermining [1,2]-aryl shift. A stronger CH···O interaction in the major transition state was found to contribute to the high levels of enantioselectivity. A more bulky catalyst (TRIP) was found to impede the formation of the key CH···O interaction, leading to lower levels of enantioselectivity.

Putting the Puzzle Together To Get the Whole Picture: Molecular Basis of the Affinity of Two Steroid Derivatives to Acetylcholinesterase.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that has no cure because its etiology is still unknown, and its main treatment is the administration of acetylcholinesterase (AChE) inhibitors. The study of the mechanism of action of this family of compounds is critical for the design of new more potent and specific inhibitors. In this work, we study the molecular basis of an uncompetitive inhibitor (compound 1, 2ß, 3α-dihydroxy-5α-cholestan-6-one disulfate), which we have proved to be a peripheral anionic site (PAS)-binding AChE inhibitor. The pipeline designed in this work is key to the development of other PAS inhibitors that not only inhibit the esterase action of the enzyme but could also modulate the non-cholinergic functions of AChE linked to the process of amylogenesis. Our studies showed that 1 inhibits the enzyme not simply by blocking the main gate but by an allosteric mechanism. A detailed and careful analysis of the ligand binding position and the protein dynamics, particularly regarding their secondary gates and active site, was necessary to conclude this. The same analysis was executed with an inactive analogue (compound 2, 2ß, 3α-dihydroxy-5α-cholestan-6-one). Our first computational results showed no differences in affinity to AChE between both steroids, making further analysis necessary. This work highlights the variables to be considered and develops a refined methodology, for the successful design of new potent dual-action drugs for AD, particularly PAS inhibitors, an attractive strategy to combat AD.

Detection and treatment of Trypanosoma cruzi: a patent review (2011-2015).

INTRODUCTION: Trypanosoma cruzi is the etiologic agent of American trypanosomiasis (Chagas disease), which is one of the important parasitic diseases worldwide. The number of infected people with T. cruzi diminished from 18 million in 1991 to 6 million in 2010, but it is still the most prevalent parasitic disease in the Americas. The existing chemotherapy is still deficient and based on two drugs: nifurtimox and benznidazole, which are not FDA-approved in the United States. AREAS COVERED: This review covers the current and future directions of Chagas disease chemotherapy based on drugs that interfere with relevant metabolic pathways. This article also illustrates the challenges of diagnosis, which in recent infections, is only detected when the parasitemia is high (direct detection); whereas, in the chronic phase is reached after multiple serological tests. EXPERT OPINION: The current chemotherapy is associated with long term treatments and severe side effects. Nifurtimox and benznidazole are able to cure at least 50% of recent infections. Nevertheless, they suffer from major drawbacks: selective drug sensitivity on different T. cruzi strains and serious side effects. The aim of this review is focused on presenting an up-to-date status of the chemotherapy and diagnosis.

Approaches for Designing new Potent Inhibitors of Farnesyl Pyrophosphate Synthase.

INTRODUCTION: Farnesyl pyrophosphate synthase (FPPS) catalyzes the condensation of isopentenyl diphosphate with dimethylallyl diphosphate to give rise to one molecule of geranyl diphosphate, which on a further reaction with another molecule of isopentenyl diphosphate forms the 15-carbon isoprenoid farnesyl diphosphate. This molecule is the obliged precursor for the biosynthesis of sterols, ubiquinones, dolichols, heme A, and prenylated proteins. The blockade of FPPS prevents the synthesis of farnesyl diphosphate and the downstream essential products. Due to its crucial role in isoprenoid biosynthesis, this enzyme has been winnowed as a molecular target for the treatment of different bone disorders and to control parasitic diseases, particularly, those produced by trypanosomatids and Apicomplexan parasites. AREAS COVERED: This article discusses some relevant structural features of farnesyl pyrophosphate synthase. It also discusses the precise mode of action of relevant modulators, including both bisphosphonate and non-bisphosphonate inhibitors and the recent advances made in the development of effective inhibitors of the enzymatic activity of this target enzyme. EXPERT OPINION: Notwithstanding their lack of drug-like character, bisphosphonates are still the most advantageous class of inhibitors of the enzymatic activity of farnesyl pyrophosphate synthase. The poor drug-like character is largely compensated by the high affinity of the bisphosphonate moiety by bone mineral hydroxyapatite in humans. Several bisphosphonates are currently in use for the treatment of a variety of bone disorders. Currently, the great prospects that bisphosphonates behave as antiparasitic agents is due to their accumulation in acidocalcisomes, organelles with equivalent composition to bone mineral, hence facilitating their antiparasitic action.

Activity of Fluorine-Containing Analogues of WC-9 and Structurally Related Analogues against Two Intracellular Parasites: Trypanosoma cruzi and Toxoplasma gondii.

Two obligate intracellular parasites, Trypanosoma cruzi, the agent of Chagas disease, and Toxoplasma gondii, an agent of toxoplasmosis, upregulate the mevalonate pathway of their host cells upon infection, which suggests that this host pathway could be a potential drug target. In this work, a number of compounds structurally related to WC-9 (4-phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, were designed, synthesized, and evaluated for their effect on T. cruzi and T. gondii growth in tissue culture cells. Two fluorine-containing derivatives, the 3-(3-fluorophenoxy)- and 3-(4-fluorophenoxy)phenoxyethyl thiocyanates, exhibited half-maximal effective concentration (EC50 ) values of 1.6 and 4.9 µm, respectively, against tachyzoites of T. gondii, whereas they showed similar potency to WC-9 against intracellular T. cruzi (EC50 values of 5.4 and 5.7 µm, respectively). In addition, 2-[3- (phenoxy)phenoxyethylthio]ethyl-1,1-bisphosphonate, which is a hybrid inhibitor containing 3-phenoxyphenoxy and bisphosphonate groups, has activity against T. gondii proliferation at sub-micromolar levels (EC50 =0.7 µm), which suggests a combined inhibitory effect of the two functional groups.