Diversity-oriented synthesis yields novel multistage antimalarial inhibitors.

Antimalarial drugs have thus far been chiefly derived from two sources-natural products and synthetic drug-like compounds. Here we investigate whether antimalarial agents with novel mechanisms of action could be discovered using a diverse collection of synthetic compounds that have three-dimensional features reminiscent of natural products and are underrepresented in typical screening collections. We report the identification of such compounds with both previously reported and undescribed mechanisms of action, including a series of bicyclic azetidines that inhibit a new antimalarial target, phenylalanyl-tRNA synthetase. These molecules are curative in mice at a single, low dose and show activity against all parasite life stages in multiple in vivo efficacy models. Our findings identify bicyclic azetidines with the potential to both cure and prevent transmission of the disease as well as protect at-risk populations with a single oral dose, highlighting the strength of diversity-oriented synthesis in revealing promising therapeutic targets.

Structural basis of malaria parasite phenylalanine tRNA-synthetase inhibition by bicyclic azetidines.

The inhibition of Plasmodium cytosolic phenylalanine tRNA-synthetase (cFRS) by a novel series of bicyclic azetidines has shown the potential to prevent malaria transmission, provide prophylaxis, and offer single-dose cure in animal models of malaria. To date, however, the molecular basis of Plasmodium cFRS inhibition by bicyclic azetidines has remained unknown. Here, we present structural and biochemical evidence that bicyclic azetidines are competitive inhibitors of L-Phe, one of three substrates required for the cFRS-catalyzed aminoacylation reaction that underpins protein synthesis in the parasite. Critically, our co-crystal structure of a PvcFRS-BRD1389 complex shows that the bicyclic azetidine ligand binds to two distinct sub-sites within the PvcFRS catalytic site. The ligand occupies the L-Phe site along with an auxiliary cavity and traverses past the ATP binding site. Given that BRD1389 recognition residues are conserved amongst apicomplexan FRSs, this work lays a structural framework for the development of drugs against both Plasmodium and related apicomplexans.

Total synthesis of plukenetione A.

We describe an alkylative dearomatization/acid-mediated adamantane annulation sequence that allows facile access to type A polyprenylated acylphloroglucinol natural products including plukenetione A. Introduction of the 2-methyl-1-propenyl moiety was achieved via stereodivergent S(N)2 and S(N)1 cyclizations of allylic alcohol substrates.

Safety, tolerability, pharmacokinetics, and antimalarial efficacy of a novel Plasmodium falciparum ATP4 inhibitor SJ733: a first-in-human and induced blood-stage malaria phase 1a/b trial.

BACKGROUND: (+)-SJ000557733 (SJ733) is a novel, orally bioavailable inhibitor of Plasmodium falciparum ATP4. In this first-in-human and induced blood-stage malaria phase 1a/b trial, we investigated the safety, tolerability, pharmacokinetics, and antimalarial activity of SJ733 in humans. METHODS: The phase 1a was a single-centre, dose-escalation, first-in-human study of SJ733 allowing modifications to dose increments and dose-cohort size on the basis of safety and pharmacokinetic results. The phase 1a took place at St Jude Children's Research Hospital and at the University of Tennessee Clinical Research Center (Memphis, TN, USA). Enrolment in more than one non-consecutive dose cohort was allowed with at least 14 days required between doses. Participants were fasted in seven dose cohorts and fed in one 600 mg dose cohort. Single ascending doses of SJ733 (75, 150, 300, 600, 900, or 1200 mg) were administered to participants, who were followed up for 14 days after SJ733 dosing. Phase 1a primary endpoints were safety, tolerability, and pharmacokinetics of SJ733, and identification of an SJ733 dose to test in the induced blood-stage malaria model. The phase 1b was a single-centre, open-label, volunteer infection study using the induced blood-stage malaria model in which fasted participants were intravenously infected with blood-stage P falciparum and subsequently treated with a single dose of SJ733. Phase 1b took place at Q-Pharm (Herston, QLD, Australia) and was initiated only after phase 1a showed that exposure exceeding the threshold minimum exposure could be safely achieved in humans. Participants were inoculated on day 0 with P falciparum-infected human erythrocytes (around 2800 parasites in the 150 mg dose cohort and around 2300 parasites in the 600 mg dose cohort), and parasitaemia was monitored before malaria inoculation, after inoculation, immediately before SJ733 dosing, and then post-dose. Participants were treated with SJ733 within 24 h of reaching 5000 parasites per mL or at a clinical score higher than 6. Phase 1b primary endpoints were calculation of a parasite reduction ratio (PRR48) and parasite clearance half-life, and safety and tolerability of SJ733 (incidence, severity, and drug-relatedness of adverse events). In both phases of the trial, SJ733 hydrochloride salt was formulated as a powder blend in capsules containing 75 mg or 300 mg for oral administration. Healthy men and women (of non-childbearing potential) aged 18-55 years were eligible for both studies. Both studies are registered with ClinicalTrials.gov (NCT02661373 for the phase 1a and NCT02867059 for the phase 1b). FINDINGS: In the phase 1a, 23 healthy participants were enrolled and received one to three non-consecutive doses of SJ733 between March 14 and Dec 7, 2016. SJ733 was safe and well tolerated at all doses and in fasted and fed conditions. 119 adverse events were recorded: 54 (45%) were unrelated, 63 (53%) unlikely to be related, and two (2%) possibly related to SJ733. In the phase 1b, 17 malaria-naive, healthy participants were enrolled. Seven participants in the 150 mg dose cohort were inoculated and dosed with SJ733. Eight participants in the 600 mg dose cohort were inoculated, but two participants could not be dosed with SJ733. Two additional participants were subsequently inoculated and dosed with SJ733. SJ733 exposure increased proportional to the dose through to the 600 mg dose, then was saturable at higher doses. Fasted participants receiving 600 mg exceeded the target area under the concentration curve extrapolated to infinity (AUC0-∞) of 13 000 µg × h/L (median AUC0-∞ 24 283 [IQR 16 135-31 311] µg × h/L, median terminal half-life 17·4 h [IQR 16·1-24·0], and median timepoint at which peak plasma concentration is reached 1·0 h [0·6-1·3]), and this dose was tested in the phase 1b. All 15 participants dosed with SJ733 had at least one adverse event. Of the 172 adverse events recorded, 128 (74%) were mild. The only adverse event attributed to SJ733 was mild bilateral foot paraesthesia that lasted 3·75 h and resolved spontaneously. The most common adverse events were related to malaria. Based on parasite clearance half-life, the derived log10PRR48 and corresponding parasite clearance half-lives were 2·2 (95% CI 2·0-2·5) and 6·47 h (95% CI 5·88-7·18) for 150 mg, and 4·1 (3·7-4·4) and 3·56 h (3·29-3·88) for 600 mg. INTERPRETATION: The favourable pharmacokinetic, tolerability, and safety profile of SJ733, and rapid antiparasitic effect support its development as a fast-acting component of combination antimalarial therapy. FUNDING: Global Health Innovative Technology Fund, Medicines for Malaria Venture, and the American Lebanese Syrian Associated Charities.

Rhodium(I)-catalyzed allenic carbocyclization reaction affording delta- and epsilon-lactams.

This letter extends the scope of the rhodium(I)-catalyzed allenic Alder-ene carbocyclization reaction to the preparation of delta- and epsilon-lactams from amides. A variety of allenic propiolamides were cycloisomerized to give a number of unsaturated delta-lactams. In addition, allenic propargylamides give good yields of the corresponding epsilon-lactams. Formation of lactams possessing these ring sizes has rarely been accomplished via transition-metal-catalyzed carbon-carbon bond forming strategies. Thus, this approach provides an alternative strategy for synthesizing these substructures. [reaction: see text].

Allenes and transition metals: a diverging approach to heterocycles.

[reaction: see text] An alkynyl allene has been converted to heterocycles possessing an alpha-alkylidene cyclopentenone, a 4-alkylidene cyclopentenone, or a cross-conjugated triene. Thus, a common intermediate has been converted to three structurally unique compounds by changing only the reaction conditions and, therefore, controlling various reaction pathways.

Rhodium(I)-catalyzed ene-allene carbocyclization strategy for the formation of azepines and oxepines.

[reaction: see text] A novel strategy for the preparation of seven-membered heterocyclic compounds has been realized. Treatment of ene-allene 1 with a catalytic quantity of rhodium biscarbonyl chloride dimer affords the cyclization product 2 in moderate to high yields. The scope and limitations of this new method are currently under investigation, and the results obtained to date are discussed within.

Manganese(III)-mediated transformations of phloroglucinols: a formal oxidative [4 + 2] cycloaddition leading to bicyclo[2.2.2]octadiones.

Manganese(III)-mediated oxidative transformations of dearomatized phloroglucinol (1,3,5-trihydroxybenzene) derivatives are reported. A number of cyclization modes have been observed, including polycyclization to afford bicyclo[2.2.2]octadiones via a formal oxidative radical [4 + 2] cycloaddition.

Structurally unique inhibitors of human mitogen-activated protein kinase phosphatase-1 identified in a pyrrole carboxamide library.

Mitogen-activated protein kinase phosphatase 1 (MKP-1) is a tyrosine phosphatase superfamily member that dephosphorylates and inactivates cardinal mitogen-activated protein kinase (MAPK) substrates, such as p38, c-Jun NH(2)-terminal kinase, and extracellular signal-regulated kinase. Although these MAPK substrates regulate many essential cellular processes associated with human diseases, few pharmacological inhibitors have been described. The lack of readily available selective MKP-1 inhibitors has severely limited interrogation of its biological role and was one rationale for using a recently described tricyclic pyrrole-2-carboxamide library in our screening efforts. In this report we demonstrate the pharmacological richness of the pyrrole carboxamide library by the finding that 10 of 172 members inhibited human MKP-1. Two of the pyrrole carboxamides, PSI2106 and MDF2085, were especially notable in vitro inhibitors of recombinant human MKP-1 enzyme activity with IC(50) values of 8.0 +/- 0.9 and 8.3 +/- 0.8 microM, respectively. Both showed some selectivity for MKP-1 over the closely related phosphatases MKP-3, Cdc25B, VHR, and PTP1B. Computational examination of the surface properties near the catalytic site revealed that the phosphatases studied differ significantly in their electrostatic potential at the substrate binding site. The compounds inhibited MKP-1 reversibly but displayed mixed kinetics. Phosphatase inhibition was retained in the presence of physiologically relevant concentrations of glutathione. Molecular docking studies suggested that PSI2106 may interact with His(229) and Phe(299) on MKP-1. These results reveal the power of using a small focused library for identifying pharmacological probes.

Solution-phase synthesis of a tricyclic pyrrole-2-carboxamide discovery library applying a stetter-Paal-Knorr reaction sequence.

The solution-phase synthesis of a discovery library of 178 tricyclic pyrrole-2-carboxamides was accomplished in nine steps and seven purifications starting with three benzoyl-protected amino acid methyl esters. Further diversity was introduced by two glyoxaldehydes and 41 primary amines. The combination of Pauson-Khand, Stetter, and microwave-assisted Paal-Knorr reactions was applied as a key sequence. The discovery library was designed with the help of QikProp 2.1, and physicochemical data are presented for all pyrroles. Library members were synthesized and purified in parallel and analyzed by LC/MS. Selected compounds were fully characterized.

Heterocyclic alpha-alkylidene cyclopentenones obtained via a Pauson-Khand reaction of amino acid derived allenynes. A scope and limitation study directed toward the preparation of a tricyclic pyrrole library.

The synthesis of a novel class of tricyclic pyrroles has been accomplished by using a Pauson-Khand/Stetter/Paal-Knorr reaction sequence. Full details of the Pauson-Khand reaction of amino acid tethered allenynes 4a-e and 9a-d are disclosed. The study of this reaction led to the discovery of an unprecedented substituent effect on the diastereoselectivity of the Mo(CO)6 mediated allenic Pauson-Khand reaction. It was found that amino acid tethered allenynes with aromatic side chains afford alpha-alkylidene cyclopentenones with the opposite diastereoselectivity compared to those with aliphatic side chains. This effect has been attributed to complexation of the metal mediator to the aromatic ring in the substrate. Furthermore, an isomerization of one of the diastereomers of the alpha-alkylidene cyclopentenones was encountered, leading to eventual decomposition. The stable diastereomers were found to react well in the Stetter reaction leading to 1,4-diketones that were converted to pyrroles. The observation that the first generation of 2-alkyl-substituted pyrroles was unstable led to a second generation of 2-carboxamide pyrroles with sufficient stability for biological tests which are in progress.