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Author: Stephen P Marsden (45)


Oct
2017

The productive exploration of chemical space is an enduring challenge in chemical biology and medicinal chemistry. Natural products are biologically relevant, and their frameworks have facilitated chemical tool and drug discovery. A "top-down" synthetic approach is described that enabled a range of complex bridged intermediates to be converted with high step efficiency into 26 diverse sp-rich scaffolds.

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Oct
2017

The organocatalytic asymmetric transfer hydrogenation of N-alkyl aryl imino esters for the direct synthesis of N-alkylated arylglycinate esters is reported. High yields and enantiomeric ratios were obtained, and tolerance to a diverse set of functional groups facilitated the preparation of more complex molecules as well as intermediates for active pharmaceuticals. A simple recycling protocol was developed for the Brønsted acid catalyst which could be reused through five cycles with no loss of activity or selectivity.

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Oct
2016

A one-pot, three-component synthesis of α-pyridyl, α-substituted amino acid derivatives is described. The key transformation is a direct, precious-metal-free heteroarylation of readily available, amino acid derived azlactones with electrophilically activated pyridine N-oxides. The resulting intermediates can be used directly as efficient acylating agents for a range of nucleophiles, leading to the heteroarylated amino acid derivatives in a single vessel.

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Oct
2016

Evaluating New Chemistry to Drive Molecular Discovery: Fit for Purpose?

Angew Chem Int Ed Engl 2016 Oct 30;55(44):13650-13657. Epub 2016 Aug 30.
Daniel J Foley, Adam Nelson, Stephen P Marsden
As our understanding of the impact of specific molecular properties on applications in discovery-based disciplines improves, the extent to which published synthetic methods meet (or do not meet) desirable criteria is ever clearer. Herein, we show how the application of simple (and in many cases freely available) computational tools can be used to develop a semiquantitative understanding of the potential of new methods to support molecular discovery. This analysis can, among other things, inform the design of improved substrate scoping studies; direct the prioritization of specific exemplar structures for synthesis; and substantiate claims of potential future applications for new methods.

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Jul
2016

A synthetic approach to diverse scaffolds was developed that was inspired by diterpene biosynthesis. Initial scaffolds, generated using Diels-Alder reactions of furyl-functionalised amines, were transformed into alternative scaffolds using cleavage, ring expansion, annulation and rearrangement reactions. In total, 25 diverse scaffolds were prepared that were shown to have high natural product-likeness.

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Jun
2016

Complementary cyclisation reactions of hex-2-ene-1,6-diamine derivatives were exploited in the synthesis of alternative molecular scaffolds. The value of the synthetic approach was analysed using LLAMA, an open-access computational tool for assessing the lead-likeness and novelty of molecular scaffolds.

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Dec
1969

A convenient, one-pot, two-component synthesis of 2-(1-amidoalkyl)pyridines is reported, based upon the substitution of suitably-activated pyridine N-oxides by azlactone nucleophiles, followed by decarboxylative azlactone ring-opening. The synthesis obviates the need for precious metal catalysts to achieve a formal enolate arylation reaction, and constitutes a formally 'umpoled' approach to this valuable class of bioactive structures.

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Jun
2015

A powerful strategy for the efficient lead-oriented synthesis of novel molecular scaffolds is demonstrated. Twenty two scaffolds were prepared from just four α-amino acid-derived building blocks and a toolkit of six connective reactions. Importantly, each individual scaffold has the ability to specifically target lead-like chemical space.

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Jun
2015

The application of [4+2] cycloadditions between alkenes and an N-benzoyl iminium species, generated in situ under acidic conditions, is described in the synthesis of diverse molecular scaffolds. The key reaction led to the formation of cyclic imidates in good yield and with high regioselectivity. It was demonstrated that the cyclic imidates may be readily converted into 1,3-amino alcohols.

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Jun
2015

The design, synthesis and decoration of six small molecule libraries is described. Each library was inspired by structures embedded in the framework of specific alkaloid natural products. The development of optimised syntheses of the required molecular scaffolds is described, in which reactions including Pd-catalysed aminoarylation and diplolar cycloadditions have been exploited as key steps.

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Jan
2015

Controlling the properties of lead molecules is critical in drug discovery, but sourcing large numbers of lead-like compounds for screening collections is a major challenge. A unified synthetic approach is described that enabled the synthesis of 52 diverse lead-like molecular scaffolds from a minimal set of 13 precursors. The divergent approach exploited a suite of robust, functional group-tolerant transformations.

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Dec
2014

The use of picolinic acid amide derivatives as an effective family of bidentate ligands for copper-catalysed aryl ether synthesis is reported. A fluorine-substituted ligand gave good results in the synthesis of a wide range of aryl ethers. Even bulky phenols, known to be very challenging substrates, were shown to react with aryl iodides with excellent yields using these ligands.

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Sep
2014

The behavior of electron-rich alkenes in rhodium-catalyzed C-H activation/annulation reactions is investigated. Vinyl acetate emerges as a convenient acetylene equivalent, facilitating the synthesis of sixteen 3,4-unsubstituted isoquinolones, as well as select heteroaryl-fused pyridones. The complementary regiochemical preferences of enol ethers versus enol esters/enamides is discussed.

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Sep
2014

Rh-catalysed conjugate additions of 2-aminophenyl boronic acid derivatives were exploited in diastereoselective and asymmetric syntheses of tetrahydroquinolines. In both cases, combinatorial variation of the substitution of the tetrahydroquinoline ring system was possible.

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May
2014

Cu-catalysed arylation reactions devoted to the formation of C-C and C-heteroatom bonds (Ullmann-type couplings) have acquired great importance in the last decade. This review discusses the history and development of coupling reactions between aryl halides and various classes of nucleophiles, focusing mostly on the different mechanisms proposed through the years. Selected mechanistic investigations are treated more in depth than others.

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Apr
2012

Since their discovery in 1997, iridium-catalysed asymmetric allylic substitutions have been developed into a broadly applicable tool for the synthesis of chiral building blocks via C-C and C-heteroatom bond formation. The remarkable generality of these reactions and the high levels of regio- and enantioselectivity that are usually obtained in favour of the branched products have been made possible by a thorough investigation of the catalyst system and its mode of action. Therefore, today the Ir-catalysed asymmetric allylic substitution is a powerful reaction in the organic chemist's repertoire and has been used extensively for several applications.

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Jul
2011

The sequential use of Cu-catalyzed asymmetric allylic alkylation, olefin cross-metathesis, and Ir-catalyzed asymmetric allylic amination allows the concise, stereodivergent synthesis of complex chiral amines with complete regiocontrol and good diastereoselectivity, exemplified by the synthesis of a pair of diastereoisomeric unnatural branched amino acid derivatives.

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Oct
2010

Non-TST behavior has recently attracted a great deal of attention. If such behavior is general, then the standard way in which synthetic chemists rationalize and predict reactivity and selectivity would be at least partially invalid. The work in this article was inspired by recent results which highlighted a departure from the predictions of TST for rationalization of the regiochemical outcome of the hydroboration reaction mechanism, suggesting that the isomeric product ratios arise because of nonstatistical dynamical effects (J.

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Mar
2010

Amines have been directly alkylated with alcohols using 1 mol% [Cp*IrI(2)](2) catalyst in water in the absence of base or other additives.

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Oct
2009

The stereochemistry of the reaction between cyclopentyne and ethene has been modeled using statistical methods, based on RRKM theory and a master equation analysis, and by molecular dynamics. We show that the stereochemical retention observed experimentally is not compatible with statistical models that invoke a diradical mechanism but that it can be rationalized through analysis of short time diradical dynamics. Within the first approximately 400 fs, reaction occurs from the initial diradical adduct to form a carbene, which may subsequently isomerize to give the final product.

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May
2009

Transition-metal-catalyzed hydrogen-transfer reactions have been used for the conversion of alcohols into benzimidazoles and aldehydes into benzoxazoles and benzothiazoles.

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Dec
1969

For over 30 years, rapamycin has generated a sustained and intense interest from the scientific community as a result of its exceptional pharmacological properties and challenging structural features. In addition to its well known therapeutic value as a potent immunosuppressive agent, rapamycin and its derivatives have recently gained prominence for the treatment of a wide variety of other human malignancies. Herein we disclose full details of our extensive investigation into the synthesis of rapamycin that culminated in a new and convergent preparation featuring a macro-etherification/catechol-templating strategy for construction of the macrocyclic core of this natural product.

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Sep
2008

The Pd-catalysed asymmetric intramolecular alpha-arylation of amide enolates containing heteroatom substituents gives chiral 3-alkoxy or 3-aminooxindoles in high yield and with enantioselectivities up to 97% ee when a new chiral N-heterocyclic carbene ligand is used.

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Sep
2008

Total syntheses of the natural immunosuppressant myriocin (1) and the equipotent unnatural analogue 2-epi-myriocin (in protected form) have been achieved through a common strategy. The key transformations are the efficient synthesis of a quaternary (E)-vinylglycine by asymmetric deconjugative alkylation of a dehydroamino acid and an unusually highly diastereoselective dihydroxylation of the vinylglycine alkene.

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Sep
2008

A direct convergent two-component synthesis of quinolines from alpha,beta-unsaturated ketones and o-aminophenylboronic acid derivatives is reported. The reaction is regiocomplementary to the traditional Skraup-Doebner-Von Miller synthesis and proceeds under basic rather than strongly acidic conditions. Quinolines substituted in the benzenoid ring can be accessed by using substituted o-aminophenylboronates prepared by direct palladium-catalyzed borylation of the corresponding o-bromoanilines.

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Aug
2008

Medicinally important 3-alkoxy-3-aryloxindoles are conveniently prepared by the rapid microwave-promoted palladium-catalyzed intramolecular enolate arylation of mandelate-derived anilides.

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Jul
2008

A novel approach to the valuable quaternary 3-aminooxindole skeleton is reported on the basis of intramolecular arylation of enolates of substituted amino acids. The reaction tolerates dialkyl- and arylalkylamines as well as a range of carbon substituents (primary and secondary alkyl, aryl). The cyclization of N-indolyl-substituted substrates is accompanied by direct C-H arylation of the indole, leading to indolo-fused benzodiazepines.

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Jun
2008

The first examples of heterocycle synthesis by iminophosphorane formation/intramolecular aza-Wittig cyclizations that are catalytic in the organophosphorus component are reported. The reaction has been demonstrated in the synthesis of both azine (phenanthridine) and azole (benzoxazole) heterocycles. Catalyst loadings down to 1 mol % have been used with little or no loss in reaction efficiency.

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Jan
2008

Tashiromine 1 is a naturally occurring indolizidine alkaloid. It has been the subject of thirteen successful total syntheses to date. Our own approach centres on the stereoselective construction of the indolizidine core by capture of an electrophilic acyliminium species by a pendant allylsilane.

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Dec
2007

The use of 2H NMR spectroscopy as a tool for the analysis of enantiomeric purity is reported. Enantiopure isotopically chiral substrates bearing a monodeuterated methylene unit were prepared; introduction of an additional asymmetric center leads to diastereomers which can be distinguished by 2H NMR on a standard spectrometer. The assays allow for simple semiquantitative analysis of asymmetric transformations.

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Sep
2007

A wide variety of P-stereogenic aryldialkylphosphines were prepared in enantioenriched form by a systematic diversification of the (-)-sparteine-mediated dynamic kinetic resolution of racemic lithiophosphine-boranes reported by Livinghouse. Excellent asymmetric induction was observed provided that the intermediate lithiophosphine/sparteine complex precipitated from solution; more soluble derivatives returned poor ee's or racemic material. The resulting phosphine-boranes were deprotected and used as reagents in the desymmetrizing asymmetric aza-Wittig reaction of 2-alkyl-2-(3-azidopropyl)cyclohexane-1,3-diones, delivering the highest ee's yet observed in this process (up to 84% ee).

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Nov
2006

A concise and convergent eight-step synthesis of the antifungal metabolite monocerin 1 is reported. The key step involves an allylsilane metathesis/aldehyde condensation sequence to establish the core 2,3,5-trisubstituted tetrahydrofuran. End-game approaches based around intramolecular Heck chemistry revealed an interesting example of formal 6-endo cyclisation, the origin of which was probed using model substrates.

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Nov
2006

A two-step protocol for the asymmetric synthesis of protected quaternary (E)-vinylglycines from simple aldehydes is reported. The key step is a regiocontrolled deconjugative asymmetric alkylation of dehydroamino acids, giving the targets as single geometric isomers with high diastereoselectivity (92-96% de). The products can be converted to valuable quaternary beta-amino alcohols by chemoselective reduction.

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Sep
2006

Readily prepared 2-alkyl-2-azidopropylcycloalkyl-1,3-diones undergo intramolecular Schmidt rearrangement with a range of hard Lewis acids, leading to indolizidinediones and pyrroloazepinediones. Chiral aluminium-based Lewis acids could also be used to mediate this symmetry-breaking transformation, but no significant asymmetric induction was observed.

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Aug
2005

Allenylsilanes are useful intermediates in organic synthesis. An attractive, convergent but little used approach for their synthesis is the alkylidenation of stable silylketenes. Reactions thus far have been limited to the use of unsubstituted silylketenes (or equivalents) with stabilised or semi-stabilised ylides only.

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Feb
2006

[reaction: see text] Putative enantioenriched carbenoid species, (R)-1-chloro-2-phenylethylmagnesium chloride (9) and (S)-1-chloro-2-phenylethyllithium (26), generated in situ by sulfoxide ligand exchange from (-)-(R(S),R)-1-chloro-2-phenylethyl p-tolyl sulfoxide (8), effected the stereocontrolled homologation of boronic esters. sec-Alcohols derived from the product boronates by oxidation with basic hydrogen peroxide exhibited % ee closely approaching that of sulfoxide 8 in examples employing Li-carbenoid 26.

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Nov
2005

[reaction: see text] A practical and general two-step synthesis of carbamate-protected (E)-vinylglycines from aliphatic aldehydes is reported. The key step involves the kinetic alpha-protonation of dianionic dienolates derived from dehydroamino acids.

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Aug
2005

The condensation of substituted allylsiloxanes with aldehydes leads to the highly stereoselective construction of 2,3,4,5-tetrasubstituted tetrahydrofurans. With electron-rich aryl and alpha,beta-unsaturated aldehydes as substrates, the stereochemical outcome at C5 can be dictated by appropriate choice of Lewis acid. The reaction has been applied to a concise (nine step) synthesis of (+)-virgatusin (ent-1).

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Oct
2004

A novel one-pot, two-component condensation reaction between readily available allylsiloxanes and electron-rich aldehydes generates aryltetralins with complete control of stereochemistry.

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Oct
2004

The reaction of ring-closing metathesis-derived cyclic allylsiloxanes 3 with aldehydes in the presence of a Lewis acid gives 2,3,4-trisubstituted tetrahydrofurans related to the furanolignan family of natural products. The reactions proceed with complete 3,4-trans stereoselectivity, whereas the C-2 stereochemistry depends on both the aldehyde and Lewis acid used. When boron trifluoride etherate is used with aliphatic or electronically neutral aryl aldehydes, the reactions favor the production of the 2,3-cis isomer 8, whereas electron-rich aryl aldehydes lead to the 2,3-trans isomer 9 by Lewis acid-mediated isomerization of the kinetically favored cis isomer.

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Feb
2004

Bowman-Birk inhibitor analogues containing 2, 3 and 4-carbon analogues of the natural disulfide were synthesised via solid phase microwave-assisted RCM and found to have K(i) values against chymotrypsin in the low to sub-micromolar range, the best replacement for the disulfide arising from the linkage by RCM of two l-homoallylglycine residues.

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