Improving Data and Prediction Quality of High-Throughput Perovskite Synthesis with Model Fusion.

Combinatorial fusion analysis (CFA) is an approach for combining multiple scoring systems using the rank-score characteristic function and cognitive diversity measure. One example is to combine diverse machine learning models to achieve better prediction quality. In this work, we apply CFA to the synthesis of metal halide perovskites containing organic ammonium cations via inverse temperature crystallization. Using a data set generated by high-throughput experimentation, four individual models (support vector machines, random forests, weighted logistic classifier, and gradient boosted trees) were developed. We characterize each of these scoring systems and explore 66 possible combinations of the models. When measured by the precision on predicting crystal formation, the majority of the combination models improves the individual model results. The best combination models outperform the best individual models by 3.9 percentage points in precision. In addition to improving prediction quality, we demonstrate how the fusion models can be used to identify mislabeled input data and address issues of data quality. In particular, we identify example cases where all single models and all fusion models do not give the correct prediction. Experimental replication of these syntheses reveals that these compositions are sensitive to modest temperature variations across the different locations of the heating element that can hinder or enhance the crystallization process. In summary, we demonstrate that model fusion using CFA can not only identify a previously unconsidered influence on reaction outcome but also be used as a form of quality control for high-throughput experimentation.

Synthetic ozonide drug candidate OZ439 offers new hope for a single-dose cure of uncomplicated malaria.

Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate designed to provide a single-dose oral cure in humans. OZ439 has successfully completed Phase I clinical trials, where it was shown to be safe at doses up to 1,600 mg and is currently undergoing Phase IIa trials in malaria patients. Herein, we describe the discovery of OZ439 and the exceptional antimalarial and pharmacokinetic properties that led to its selection as a clinical drug development candidate. In vitro, OZ439 is fast-acting against all asexual erythrocytic Plasmodium falciparum stages with IC(50) values comparable to those for the clinically used artemisinin derivatives. Unlike all other synthetic peroxides and semisynthetic artemisinin derivatives, OZ439 completely cures Plasmodium berghei-infected mice with a single oral dose of 20 mg/kg and exhibits prophylactic activity superior to that of the benchmark chemoprophylactic agent, mefloquine. Compared with other peroxide-containing antimalarial agents, such as the artemisinin derivatives and the first-generation ozonide OZ277, OZ439 exhibits a substantial increase in the pharmacokinetic half-life and blood concentration versus time profile in three preclinical species. The outstanding efficacy and prolonged blood concentrations of OZ439 are the result of a design strategy that stabilizes the intrinsically unstable pharmacophoric peroxide bond, thereby reducing clearance yet maintaining the necessary Fe(II)-reactivity to elicit parasite death.

The comparative antimalarial properties of weak base and neutral synthetic ozonides.

Thirty-three N-acyl 1,2,4-dispiro trioxolanes (secondary ozonides) were synthesized. For these ozonides, weak base functional groups were not required for high antimalarial potency against Plasmodium falciparum in vitro, but were necessary for high antimalarial efficacy in Plasmodium berghei-infected mice. A wide range of LogP/D(pH)(7.4) values were tolerated, although more lipophilic ozonides tended to be less metabolically stable.

Identification of an antimalarial synthetic trioxolane drug development candidate.

The discovery of artemisinin more than 30 years ago provided a completely new antimalarial structural prototype; that is, a molecule with a pharmacophoric peroxide bond in a unique 1,2,4-trioxane heterocycle. Available evidence suggests that artemisinin and related peroxidic antimalarial drugs exert their parasiticidal activity subsequent to reductive activation by haem, released as a result of haemoglobin digestion by the malaria-causing parasite. This irreversible redox reaction produces carbon-centred free radicals, leading to alkylation of haem and proteins (enzymes), one of which--the sarcoplasmic-endoplasmic reticulum ATPase PfATP6 (ref. 7)--may be critical to parasite survival. Notably, there is no evidence of drug resistance to any member of the artemisinin family of drugs. The chemotherapy of malaria has benefited greatly from the semi-synthetic artemisinins artemether and artesunate as they rapidly reduce parasite burden, have good therapeutic indices and provide for successful treatment outcomes. However, as a drug class, the artemisinins suffer from chemical (semi-synthetic availability, purity and cost), biopharmaceutical (poor bioavailability and limiting pharmacokinetics) and treatment (non-compliance with long treatment regimens and recrudescence) issues that limit their therapeutic potential. Here we describe how a synthetic peroxide antimalarial drug development candidate was identified in a collaborative drug discovery project.

Structure-Activity Relationship of the Antimalarial Ozonide Artefenomel (OZ439).

Building on insights gained from the discovery of the antimalarial ozonide arterolane (OZ277), we now describe the structure-activity relationship (SAR) of the antimalarial ozonide artefenomel (OZ439). Primary and secondary amino ozonides had higher metabolic stabilities than tertiary amino ozonides, consistent with their higher pKa and lower log D7.4 values. For primary amino ozonides, addition of polar functional groups decreased in vivo antimalarial efficacy. For secondary amino ozonides, additional functional groups had variable effects on metabolic stability and efficacy, but the most effective members of this series also had the highest log D7.4 values. For tertiary amino ozonides, addition of polar functional groups with H-bond donors increased metabolic stability but decreased in vivo antimalarial efficacy. Primary and tertiary amino ozonides with cycloalkyl and heterocycle substructures were superior to their acyclic counterparts. The high curative efficacy of these ozonides was most often associated with high and prolonged plasma exposure, but exposure on its own did not explain the presence or absence of either curative efficacy or in vivo toxicity.

Spiro and dispiro-1,2,4-trioxolanes as antimalarial peroxides: charting a workable structure-activity relationship using simple prototypes.

This paper describes the discovery of synthetic 1,2,4-trioxolane antimalarials and how we established a workable structure-activity relationship in the context of physicochemical, biopharmaceutical, and toxicological profiling. An achiral dispiro-1,2,4-trioxolane (3) in which the trioxolane is flanked by a spiroadamantane and spirocyclohexane was rapidly identified as a lead compound. Nonperoxidic 1,3-dioxolane isosteres of 3 were inactive as were trioxolanes without the spiroadamantane. The trioxolanes were substantially less effective in a standard oral suspension formulation compared to a solubilizing formulation and were more active when administered subcutaneously than orally, both of which suggest substantial biopharmaceutical liabilities. Nonetheless, despite their limited oral bioavailability, the more lipophilic trioxolanes generally had better oral activity than their more polar counterparts. In pharmacokinetic experiments, four trioxolanes had high plasma clearance values, suggesting a potential metabolic instability. The toxicological profiles of two trioxolanes were comparable to that of artesunate.

The structure-activity relationship of the antimalarial ozonide arterolane (OZ277).

The structure and stereochemistry of the cyclohexane substituents of analogues of arterolane (OZ277) had little effect on potency against Plasmodium falciparum in vitro. Weak base functional groups were not required for high antimalarial potency, but they were essential for high antimalarial efficacy in P. berghei-infected mice. Five new ozonides with antimalarial efficacy and ADME profiles superior or equal to that of arterolane were identified.

Weak base dispiro-1,2,4-trioxolanes: potent antimalarial ozonides.

Thirty weak base 1,2,4-dispiro trioxolanes (secondary ozonides) were synthesized. Amino amide trioxolanes had the best combination of antimalarial and biopharmaceutical properties. Guanidine, aminoxy, and amino acid trioxolanes had poor antimalarial activity. Lipophilic trioxolanes were less stable metabolically than their more polar counterparts.

Effect of functional group polarity on the antimalarial activity of spiro and dispiro-1,2,4-trioxolanes.

Based on the structures of several lipophilic trioxolane antimalarial prototypes, we set out to determine which functional groups were associated with good antimalarial profiles and identify more polar (lower LogP/LogD) lead compounds with good physicochemical properties. More lipophilic trioxolanes tended to have better oral activities than their more polar counterparts. Trioxolanes with a wide range of neutral and basic, but not acidic, functional groups had good antimalarial profiles.

Dispiro-1,2,4-trioxane analogues of a prototype dispiro-1,2,4-trioxolane: mechanistic comparators for artemisinin in the context of reaction pathways with iron(II).

Single electron reduction of the 1,2,4-trioxane heterocycle of artemisinin (1) forms primary and secondary carbon-centered radicals. The complex structure of 1 does not lend itself to a satisfactory dissection of the electronic and steric effects that influence the formation and subsequent reaction of these carbon-centered free radicals. To help demarcate these effects, we characterized the reactions of achiral dispiro-1,2,4-trioxolane 4 and dispiro-1,2,4-trioxanes 5-7 with ferrous bromide and 4-oxo-TEMPO. Our results suggest a small preference for attack of Fe(II) on the nonketal peroxide oxygen atom of 1. For 4, but not for 5 and 6, there was a strong preference for attack of Fe(II) on the less hindered peroxide bond oxygen atom. The steric hindrance afforded by a spiroadamantane in a five-membered trioxolane is evidently much greater than that for a corresponding six-membered trioxane. Unlike 1, 5-7 fragment by entropically favored beta-scission pathways forming relatively stable alpha-oxa carbon-centered radicals. These data suggest that formation of either primary or secondary carbon-centered radicals is a necessary but insufficient criterion for antimalarial activity of 1 and synthetic peroxides.

Synthetic peroxides as antimalarials.

The discovery of artemisinin in 1971 initiated a new era in antimalarial chemotherapy. Although the clinically useful semisynthetic artemisinin derivatives are rapid acting and potent antimalarial drugs, they have short half-lives and must be administered over a period of 5-7 days, leading to noncompliance and recrudescence. With this in view, many synthetic antimalarial peroxides have been prepared. Yet, identification of orally active synthetic peroxide drug development candidates that are easily synthesized, inexpensive, and with good biopharmaceutical properties has been surprisingly difficult. In this review, we document the pitfalls and progress made in this endeavor. For each of 15 synthetic peroxide structural classes, we note highlights of the synthetic routes, product stereochemistry, and origin of the peroxide O atoms. Both in vitro and in vivo antimalarial data are then discussed and any SAR noted. Available data indicates that several synthetic 1,2,4-trioxanes are only marginally less effective than the semisynthetic artemisinins. Within a given peroxide chemical family, the more lipophilic members are more potent and possess better oral antimalarial activity in animal models than their more polar counterparts. This poses a challenge to identify peroxide structures with suitable "drug-like" physicochemical properties. Nonetheless, substantial progress has been made in the identification of a new generation of synthetic antimalarial peroxides.

Synthesis of tetrasubstituted ozonides by the Griesbaum coozonolysis reaction: diastereoselectivity and functional group transformations by post-ozonolysis reactions.

The diastereoselectivity of the Griesbaum coozonolysis reaction with O-methyl 2-adamantanone oxime and 4-substituted cyclohexanones reveals that the major tetrasubstituted ozonide isomers possess cis configurations, suggesting a preferred axial attack of the carbonyl oxide on the cyclohexanone dipolarophiles. It is evident that these tetrasubstituted ozonides are quite stable to triphenylphosphine, borohydrides, hydrazine, alkyllithiums, Grignard reagents, mercaptides, and aqueous KOH as illustrated by the synthesis of amine, alcohol, acid, ester, ether, sulfide, sulfone, and heterocycle-functionalized ozonides by a wide range of post-ozonolysis transformations.