Synthesis and Configurational Assignment of Vinyl Sulfoximines and Sulfonimidamides.

Vinyl sulfones and sulfonamides are valued for their use as electrophilic warheads in covalent protein inhibitors. Conversely, the S(VI) aza-isosteres thereof, vinyl sulfoximines and sulfonimidamides, are far less studied and have yet to be applied to the field of protein bioconjugation. Herein, we report a range of different synthetic methodologies for constructing vinyl sulfoximine and vinyl sulfonimidamide architectures that allows access to new areas of electrophilic chemical space. We demonstrate how late-stage functionalization can be applied to these motifs to incorporate alkyne tags, generating fully functionalized probes for future chemical biology applications. Finally, we establish a workflow for determining the absolute configuration of enantioenriched vinyl sulfoximines and sulfonimidamides by comparing experimentally and computationally determined electronic circular dichroism spectra, enabling access to configurationally assigned enantiomeric pairs by separation.

Multiparameter Kinetic Analysis for Covalent Fragment Optimization by Using Quantitative Irreversible Tethering (qIT).

Chemical probes that covalently modify cysteine residues in a protein-specific manner are valuable tools for biological investigations. Covalent fragments are increasingly implemented as probe starting points, but the complex relationship between fragment structure and binding kinetics makes covalent fragment optimization uniquely challenging. We describe a new technique in covalent probe discovery that enables data-driven optimization of covalent fragment potency and selectivity. This platform extends beyond the existing repertoire of methods for identifying covalent fragment hits by facilitating rapid multiparameter kinetic analysis of covalent structure-activity relationships through the simultaneous determination of Ki , kinact and intrinsic reactivity. By applying this approach to develop novel probes against electrophile-sensitive kinases, we showcase the utility of the platform in hit identification and highlight how multiparameter kinetic analysis enabled a successful fragment-merging strategy.

Rapid Assembly of Saturated Nitrogen Heterocycles in One-Pot: Diazo-Heterocycle "Stitching" by N-H Insertion and Cyclization.

Methods that provide rapid access to new heterocyclic structures in biologically relevant chemical space provide important opportunities in drug discovery. Here, a strategy is described for the preparation of 2,2-disubstituted azetidines, pyrrolidines, piperidines, and azepanes bearing ester and diverse aryl substituents. A one-pot rhodium catalyzed N-H insertion and cyclization sequence uses diazo compounds to stitch together linear 1,m-haloamines (m=2-5) to rapidly assemble 4 -, 5 -, 6 -, and 7 -membered saturated nitrogen heterocycles in excellent yields. Over fifty examples are demonstrated, including examples with diazo compounds derived from biologically active compounds. The products can be functionalized to afford α,α-disubstituted amino acids and applied to fragment synthesis.

High-Throughput Kinetic Analysis for Target-Directed Covalent Ligand Discovery.

Cysteine-reactive small molecules are used as chemical probes of biological systems and as medicines. Identifying high-quality covalent ligands requires comprehensive kinetic analysis to distinguish selective binders from pan-reactive compounds. Quantitative irreversible tethering (qIT), a general method for screening cysteine-reactive small molecules based upon the maximization of kinetic selectivity, is described. This method was applied prospectively to discover covalent fragments that target the clinically important cell cycle regulator Cdk2. Crystal structures of the inhibitor complexes validate the approach and guide further optimization. The power of this technique is highlighted by the identification of a Cdk2-selective allosteric (type IV) kinase inhibitor whose novel mode-of-action could be exploited therapeutically.

Palladium-Catalyzed Directed C(sp3)-H Arylation of Saturated Heterocycles at C-3 Using a Concise Optimization Approach.

Saturated heterocycles, such as THFs, pyrrolidines, piperidines and THPs, are essential components of many biologically active compounds. Examples of C-H functionalization on these important ring systems remain scarce, especially at unactivated positions. Here we report the development of conditions for the palladium-catalyzed stereoselective C(sp3)-H arylation at unactivated 3-positions of 5- and 6-membered N- and O-heterocycles with aminoquinoline directing groups. Subtle differences in substrate structures altered their reactivity significantly; and different conditions were required to achieve high yields in each case. Successful conditions were developed using a short empirical optimization approach to cover reaction space with a limited set of variables. Excellent cis-selectivity was achieved in all cases, except for the THP substrate where minor trans-products were formed through a different palladacyclic intermediate. Here, differences in reactivity and selectivity with other directing groups were examined.

Synthesis of cis-C-iodo-N-tosyl-aziridines using diiodomethyllithium: reaction optimization, product scope and stability, and a protocol for selection of stationary phase for chromatography.

The preparation of C-iodo-N-Ts-aziridines with excellent cis-diastereoselectivity has been achieved in high yields by the addition of diiodomethyllithium to N-tosylimines and N-tosylimine-HSO2Tol adducts. This addition-cyclization protocol successfully provided a wide range of cis-iodoaziridines, including the first examples of alkyl-substituted iodoaziridines, with the reaction tolerating both aryl imines and alkyl imines. An ortho-chlorophenyl imine afforded a ß-amino gem-diiodide under the optimized reaction conditions due to a postulated coordinated intermediate preventing cyclization. An effective protocol to assess the stability of the sensitive iodoaziridine functional group to chromatography was also developed. As a result of the judicious choice of stationary phase, the iodoaziridines could be purified by column chromatography; the use of deactivated basic alumina (activity IV) afforded high yield and purity. Rearrangements of electron-rich aryl-iodoaziridines have been promoted, selectively affording either novel α-iodo-N-Ts-imines or α-iodo-aldehydes in high yield.

Vinyl sulfonamide synthesis for irreversible tethering via a novel α-selenoether protection strategy.

Vinyl sulfonamides are valuable electrophiles for targeted protein modification and inhibition. We describe a novel approach to the synthesis of terminal vinyl sulfonamides which uses mild oxidative conditions to induce elimination of an α-selenoether masking group. The method complements traditional synthetic approaches and typically yields vinyl sulfonamides in high purity after aqueous work-up without requiring column chromatography of the final electrophilic product. The methodology is applied to the synthesis of covalent fragments for use in irreversible protein tethering and crucially enables the attachment of diverse fragments to the vinyl sulfonamide warhead via a chemical linker. Using thymidylate synthase as a model system, ethylene glycol is identified as an effective linker for irreversible protein tethering.

Regio- and Stereoselective Palladium-Catalyzed C(sp3)-H Arylation of Pyrrolidines and Piperidines with C(3) Directing Groups.

The selective synthesis of cis-3,4-disubstituted pyrrolidines and piperidines is achieved by a Pd-catalyzed C-H arylation with excellent regio- and stereoselectivity using an aminoquinoline auxiliary at C(3). The arylation conditions are silver free, use a low catalyst loading, and employ inexpensive K2CO3 as a base. Directing group removal is accomplished under new, mild conditions to access amide-, acid-, ester-, and alcohol-containing fragments and building blocks. This C-H arylation protocol enabled a short and stereocontrolled formal synthesis of (-)-paroxetine.

Synthesis and purification of iodoaziridines involving quantitative selection of the optimal stationary phase for chromatography.

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. Diiodomethyllithium is prepared by the deprotonation of diiodomethane with LiHMDS, in a THF/diethyl ether mixture, at -78 °C in the dark. These conditions are essential for the stability of the LiCHI2 reagent generated. The subsequent dropwise addition of N-Ts aldimines to the preformed diiodomethyllithium solution affords an amino-diiodide intermediate, which is not isolated. Rapid warming of the reaction mixture to 0 °C promotes cyclization to afford iodoaziridines with exclusive cis-diastereoselectivity. The addition and cyclization stages of the reaction are mediated in one reaction flask by careful temperature control. Due to the sensitivity of the iodoaziridines to purification, assessment of suitable methods of purification is required. A protocol to assess the stability of sensitive compounds to stationary phases for column chromatography is described. This method is suitable to apply to new iodoaziridines, or other potentially sensitive novel compounds. Consequently this method may find application in range of synthetic projects. The procedure involves firstly the assessment of the reaction yield, prior to purification, by (1)H NMR spectroscopy with comparison to an internal standard. Portions of impure product mixture are then exposed to slurries of various stationary phases appropriate for chromatography, in a solvent system suitable as the eluent in flash chromatography. After stirring for 30 min to mimic chromatography, followed by filtering, the samples are analyzed by (1)H NMR spectroscopy. Calculated yields for each stationary phase are then compared to that initially obtained from the crude reaction mixture. The results obtained provide a quantitative assessment of the stability of the compound to the different stationary phases; hence the optimal can be selected. The choice of basic alumina, modified to activity IV, as a suitable stationary phase has allowed isolation of certain iodoaziridines in excellent yield and purity.

Regio- and stereospecific synthesis of C-3 functionalized proline derivatives by palladium catalyzed directed C(sp3)-H arylation.

Functionalization of C(sp(3))-H bonds at the unactivated 3-position of proline derivatives has been achieved using aryl iodides and palladium catalysis. This directly affords cis-2,3-disubstituted pyrrolidines as single stereoisomers. 3-Arylation occurs in high yield under solvent-free conditions with aminoquinoline and methoxyaminoquinoline directing groups. The latter was readily removed to give primary amide derivatives with physicochemical properties appropriate for use as fragments in drug discovery.