Bioisosteric Tactics in the Discovery of Tetflupyrolimet: A New Mode-of-Action Herbicide

The last new herbicidal modes-of-action with commercial significance were introduced to the marketplace multiple decades ago. Serious weed resistance to most herbicidal classes have since emerged with widespread use. Aryl pyrrolidinone anilides represent an entirely new mode-of-action class of herbicides that interfere with de novo pyrimidine biosynthesis in plants via inhibition of dihydroorotate dehydrogenase. The chemical lead for this new herbicide class discovery was identified from high-volume sourced greenhouse screening that required structural reassignment of the hit molecule followed by an extensive synthetic optimization effort. With excellent grass weed control and pronounced safety on rice, the selected commercial development candidate has a proposed common name of tetflupyrolimet and represents the first member of the new HRAC (Herbicide Resistance Action Committee) Group 28. This paper describes the discovery path to tetflupyrolimet with an added focus on the bioisosteric modifications pursued in optimization, including replacements of the lactam core itself.

Tubulin modulating antifungal and antiproliferative pyrazinone derivatives

A novel class of synthetic tubulin polymerization disruptors, based on a substituted pyrazin-2-one core, has been discovered. These molecules have proven to be potent broad spectrum fungicides, with activity on agriculturally important ascomycete and basidiomycete pathogens. They have also been found to be particularly potent against human rhabdomyosarcoma cells. Using an efficient synthetic route, the agricultural and medicinal activity was explored.

Scalable Methodology for the Catalytic, Asymmetric α-Bromination of Acid Chlorides

The optimization of a practical, catalytic, asymmetric process for the alpha-bromination of acid chlorides to produce synthetically versatile, optically active alpha-bromoesters is reported. A range of products is produced in high enantioselectivity and moderate to good chemical yields with retention of both upon scale-up. The reactions herein are catalyzed by cinchona alkaloid derivatives, with the best performance achieved by the use of a proline cinchona alkaloid conjugate designed in a de novo fashion.

Study of the Interaction of Chlorisondamine and Chlorisondamine Analogues with an Epitope of the α-2 Neuronal Acetylcholine Nicotinic Receptor Subunit

Chlorisondamine (CHL), a neuronal nicotinic ganglionic blocker, when injected in the cerebral ventricle of rats chronically blocks the increase in locomotion and rearing by subcutaneous nicotine injection. The blocking of the ion channel(s) prevents nicotine from exerting its rewarding effects on the CNS. When administered intraperitoneally, a dose 400-500 times the intracerebroventricular one is needed to cross the blood-brain barrier and to generate the same level of nicotine antagonism, resulting in severe side-effects, thus making it unlikely to be used as a therapeutical compound. Three CHL analogues, 2-(indolin-1-yl)-N,N,N-trimethylethanaminium iodide, 2-(1,3-dioxoisoindolin-2-yl)- N,N,N-trimethylethanaminium iodide, and 2-(1H-indole-3-carboxamido)- N,N,N-trimethylethanaminium iodide, were synthesized in the hope of circumventing the parent compound's shortcomings. They all share a modified indole ring, lack the four chlorines CHL carries, and have one tertiary amine and one quaternary amine. The CHL analogues form noncovalent complexes with an epitope of the alpha-2 nicotinic receptor subunit, GEREE(p)TEEEEEEEDEN, previously proposed as the possible site of CHL interaction. Complexes were analyzed using matrix-assisted laser desorption/ionization mass spectrometry for comparison with CHL. Overall, all three analogues showed better affinity than CHL for complex formation with both the nonphosphorylated and phosphorylated epitopes.

A new approach to natural products discovery exemplified by the identification of sulfated nucleosides in spider venom

Using a new approach based on the NMR spectroscopic analysis of the entire, unpurified spider venom, we identified a family of unusual sulfated nucleoside derivatives from the venom of the hobo spider, Tegenaria agrestis. These compounds are ribonucleoside mono- and disulfates derived from guanosine and xanthosine, some of which are glycosylated, bearing one or two D-fucose units. The use of NMR spectroscopy to characterize the unfractionated venom was central to the discovery of this heretofore overlooked class of venom components.

Catalytic, asymmetric alpha-chlorination of acid halides

We present a full account of a tandem catalytic, asymmetric chlorination/esterification process that produces highly optically enriched alpha-chloroesters from inexpensive, commercially available acid halides using cinchona alkaloid derivatives as catalysts and polychlorinated quinones as halogenating agents. We have performed kinetics and control experiments to investigate the reaction mechanism and establish conditions under which the reactions can be best performed. We have developed NaH and NaHCO3 shuttle base systems as the easiest and most cost-effective ways of conducting the reactions, rendering the methodology economically competitive with known chiral halogenation procedures. We have also demonstrated the utility of our reactions by converting the products to synthetically useful derivatives.

Advances in the catalytic, asymmetric synthesis of beta-lactams

In this Account, we illustrate our contribution to the catalytic, asymmetric synthesis of beta-lactams through a flexible [2 + 2] cycloaddition strategy. We also explore the scope of our methodology and comment on future directions.

A multistage, one-pot procedure mediated by a single catalyst: a new approach to the catalytic asymmetric synthesis of beta-amino acids

A catalytic asymmetric procedure for the preparation of beta-amino acids (specifically beta-substituted aspartic acid derivatives) is reported. The cinchona alkaloid catalyst benzoylquinine (BQ) mediates up to five distinct steps of a reaction pathway, all in one reaction vessel. The products of this reaction, highly optically enriched beta-substituted aspartic acid derivatives, were prepared from N-acyl-alpha-chloroglycine esters and acid chlorides in the presence of the catalyst. This approach was also amenable to the synthesis of small polypeptides containing beta-substituted aspartic acid units, including a non-natural fragment of the antibiotic lysobactin. The addition of Lewis acids to this system was found to accelerate the rate of specific steps in the reaction pathway. Mechanistic aspects of this reaction, such as imine formation and Lewis acid chelation to the beta-lactam intermediate, were investigated through comparison of IR, NMR, and other physical data.

Alpha-imino esters: versatile substrates for the catalytic, asymmetric synthesis of alpha- and beta-amino acids and beta-lactams

The catalytic asymmetric addition of organic nucleophiles to alpha-imino esters has emerged as one of the most promising and intensely investigated routes to optically enriched alpha- and beta-amino acid derivatives and beta-lactams. The importance of alpha-imino esters stems not only from the vast appeal of the potential product classes,(1) but also from their remarkable reactivity as highly electrophilic imines. With each passing year, the number of publications concerning the asymmetric alkylation of imino esters grows significantly. The asymmetric alkylation of imines(2) and N,O-acetals has been in itself a subject of intense interest.(3) In this Account, we wish to illustrate our contribution to this timely field, as well as to highlight the seminal contributions of others.

Sequential Column Asymmetric Catalysis

Since the introduction of catalysts and reagents on solid-support, researchers have developed new reaction systems to take advantage of their insoluble nature by designing multistep reaction sequences, high-throughput purification techniques, and combinatorial synthesis methods. The continuous flow system is one of these advancements and represents the foundation of a new technique termed sequential column asymmetric catalysis (CAC). In this strategy, reagents and catalysts are attached to a solid-phase support and loaded onto sequentially-linked columns. The substrates are present in the liquid phase that flows through the column. As a substrate encounters each successive column, it grows in complexity. Consequently, one can imagine a number of flow systems that consist of columns attached in series and/or in parallel that synthesize a fairly complex molecule. Herein, we discuss the development of the sequential CAC technique, beginning with the most relevant antecedents.

The development of the first catalyzed reaction of ketenes and imines: catalytic, asymmetric synthesis of beta-lactams

We report practical methodology for the catalytic, asymmetric synthesis of beta-lactams resulting from the development of a catalyzed reaction of ketenes (or their derived zwitterionic enolates) and imines. The products of these asymmetric reactions can serve as precursors to a number of enzyme inhibitors and drug candidates as well as valuable synthetic intermediates. We present a detailed study of the mechanism of the beta-lactam forming reaction with proton sponge as the stoichiometric base, including kinetics and isotopic labeling studies. Stereochemical models based on molecular mechanics (MM) calculations are also presented to account for the observed stereoregular sense of induction in our reactions and to provide a guidepost for the design of other catalyst systems.

Bifunctional asymmetric catalysis: a tandem nucleophile/Lewis acid promoted synthesis of beta-lactams

[reaction: see text]. We describe a superior procedure for the catalytic, asymmetric synthesis of beta-lactams using a bifunctional catalyst system consisting of a chiral nucleophile and an achiral Lewis acid.

Generation of ketenes from acid chlorides using NaH/crown ether shuttle-deprotonation for use in asymmetric catalysis

[reaction: see text] We describe methodology for the in situ generation of reactive monosubstituted ketenes from acid chlorides through a shuttle deprotonation process using NaH as an inexpensive stoichiometric base and a crown ether cocatalyst. We have successfully applied this new procedure to the catalytic, asymmetric synthesis of beta-lactams and alpha-haloesters.

A catalyst that plays multiple roles: asymmetric synthesis of beta-substituted aspartic acid derivatives through a four-stage, one-pot procedure

We report a new method for the catalytic, asymmetric synthesis of beta-substituted aspartic acid derivatives in which the nucleophilic catalyst serves up to four discrete roles in a one-pot procedure: catalytic dehydrohalogenation of acid chlorides to form ketenes; catalytic dehydrohalogenation of alpha-chloroamines to form the corresponding imines; catalyzed [2 + 2]-cycloaddition to produce intermediate acyl beta-lactams; and finally, nucleophilic ring opening to afford optically enriched beta-substituted aspartic acids in high enantioselectivity and diastereoselectivity.

Catalytic, enantioselective alkylation of alpha-imino esters: the synthesis of nonnatural alpha-amino acid derivatives

Methodology for the practical synthesis of nonnatural amino acids has been developed through the catalytic, asymmetric alkylation of alpha-imino esters and N,O-acetals by enol silanes, ketene acetals, alkenes, and allylsilanes using chiral transition metal-phosphine complexes as catalysts (1-5 mol %). The alkylation products, which are prepared with high enantioselectivity (up to 99% ee) and diastereoselectivity (up to 25:1/anti:syn), are protected nonnatural amino acids that represent potential precursors to natural products and pharmaceuticals. A kinetic analysis of the catalyzed reaction of alkenes with alpha-imino esters is presented to shed light on the mechanism of this reaction.

Asymmetric catalysis on sequentially-linked columns

We report a catalytic asymmetric reaction process that involves the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of beta-lactams, to yield pure products with excellent enantio- and diastereoselectivity. We have identified several advantages to conducting chemical reactions on sequential columns, including ease of catalyst and reagent recovery and simplified purification steps that preclude the need for chromatography.

Reactive ketenes through a carbonate/amine shuttle deprotonation strategy: catalytic, enantioselective alpha-bromination of acid chlorides

[reaction: see text] We have developed an efficient methodology for the generation of ketenes by employing a catalytic shuttle base and potassium carbonate as a stoichiometric base. We have applied this technology to the catalytic, asymmetric alpha-bromination of acid chlorides.

Column asymmetric catalysis for beta-lactam synthesis

[structure] A catalytic asymmetric reaction process was designed involving the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of beta-lactams, yielding pure product after crystallization with exceptional enantio- and diastereoselectivity.

Nucleophilic metal complexes as acylation catalysts: solvent-dependent "switch" mechanisms leading to the first catalyzed Staudinger reaction

[formula: see text] Catalytic acylation using complex transition metal salts MCo(CO)4 is demonstrated. Surprisingly, a solvent-dependent mechanistic "switch" results in a Lewis acid-based acylation mechanism in nonpolar media and a nucleophilic mechanism in polar organic media. These observations lead to the first example of a catalyzed Staudinger reaction to form beta-lactams.