Catalytic, Enantioselective Synthesis of Stilbene cis-Diamines: A Concise Preparation of (-)-Nutlin-3, a Potent p53/MDM2 Inhibitor

Palladium-Catalyzed α-Arylation of Aryl Nitromethanes

Catalytic conditions for the α-arylation of aryl nitromethanes have been discovered using parallel microscale experimentation, despite two prior reports of the lack of reactivity of these aryl nitromethane precursors. The method efficiently provides a variety of substituted, isolable diaryl nitromethanes. In addition, it is possible to sequentially append two different aryl groups to nitromethane. Mild oxidation conditions were identified to afford the corresponding benzophenones via the Nef reaction, and reduction conditions were optimized to afford several diaryl methylamines.

Cinchonidinium acetate as a convenient catalyst for the asymmetric synthesis of cis-stilbenediamines

Inexpensive and readily available cinchonidinium acetate is an effective catalyst for the syn-selective aza-Henry reaction of arylnitromethanes and aryl imines. The resulting masked cis-stilbenediamine products are produced in excellent diastereoselectivity and good enantioselectivity, and enantiopure material can be achieved via recrystallization. The features of the cinchona catalyst needed for selectivity are discussed, with specific emphasis on formation of a kinetically controlled syn-product without epimerization of the highly acidic α-nitro stereocenter.

Synthesis of trifluoromethyl-containing vicinal diamines by asymmetric decarboxylative mannich addition reactions

Herein is reported a study of asymmetric decarboxylative Mannich addition reactions between (Ss)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine and Schiff bases derived from various aldehydes and lithium 2,2-diphenylglycinate. These reactions proceed with excellent diastereoselectivities and good chemical yields, providing a practical method for preparation of trifluoromethyl-containing vicinal diamines. The procedures can be conducted under convenient conditions, rendering this approach of high synthetic value.

Adaptation of a small-molecule hydrogen-bond donor catalyst to an enantioselective hetero-Diels-Alder reaction hypothesized for brevianamide biosynthesis

Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels-Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis.

Organocatalytic Asymmetric Synthesis of Dihydroisoquinolinones via a One-Pot Aza-Henry-Hemiaminalization-Oxidation Sequence

The asymmetric organocatalytic one-pot synthesis of trans-3,4-disubstituted 3,4-dihydroisoquinolin-1(2H)-ones is described. Starting from 2-(nitromethyl)benzaldehydes and various N-protected aldimines, 5 mol% of a quinine-based squaramide organocatalyst was used to synthesize the title compounds as virtually single diastereomers via an aza-Henry-hemiaminalization-oxidation sequence. Moderate to good yields (39-78%) and moderate to very good enantioselectivities (40-95% ee) were reached.

Stereoselective synthesis of 1,2-diamine containing indolines by a conjugate addition nitro-Mannich reaction

A conjugate addition nitro-Mannich reaction followed by nitro reduction and intramolecular N-arylation gives diastereomerically pure substituted 1,2-diamine containing indolines. Placing the N-arylation cyclisation handle on the imine precursor derived from an ortho-bromine substituted aromatic aldehyde gave the corresponding β-nitroamines in 55-72% yields as single diastereoisomers. Nitro reduction was effected with modified quantities of Zn/HCl and a subsequent Pd(0) catalysed Buchwald Hartwig cyclisation gave indoline products in 40-70% yields as single diastereoisomers.

Enantioselective Addition of Bromonitromethane to Aliphatic N-Boc Aldimines Using a Homogeneous Bifunctional Chiral Organocatalyst

This report details the enantioselective synthesis of β-amino-α-bromo nitroalkanes with β-alkyl substituents, using homogeneous catalysis to prepare either antipode. Use of a bifunctional Brønsted base/acid catalyst allows equal access to either enantiomer of the products, enabling the use of Umpolung Amide Synthesis (UmAS) to prepare the corresponding L- or D-α-amino amide bearing alkyl side chains - overall, in only 4 steps from aldehyde. The approach also addresses an underlying incompatibility between bromonitromethane and solid hydroxide bases.

A highly sensitive fluorescent light-up probe for real-time detection of the endogenous protein target and its antagonism in live cells

A target-specific switchable fluorescent probe for cellular Mdm2 protein detection (off–on) and drug discovery applications (on–off) targeting the p53 pathway.

Asymmetric aza-Henry reaction to provide oxindoles with quaternary carbon stereocenter catalyzed by a metal-templated chiral Brønsted base

An inert octahedral chiral-at-metal iridium(iii) complex serves as a highly effective chiral Brønsted base catalyst for implementing a quaternary carbon stereocenter.

Efficient reactivation of p53 in cancer cells by a dual MdmX/Mdm2 inhibitor

The aberrant interaction between p53 and Mdm2/MdmX is an attractive target for cancer drug discovery because the overexpression of Mdm2 and/or MdmX ultimately impairs the function of p53 in approximately half of all human cancers. Recent studies have shown that inhibition of both Mdm2 and MdmX is more efficient than that of a single target in promoting cellular apoptosis in cancers. In this study, we demonstrate that a dual small-molecule antagonist of Mdm2/MdmX can efficiently reactivate the p53 pathway in model cancer cells overexpressing MdmX and/or Mdm2. The dual antagonist was rationally designed based on segmental mutational analysis of the N-terminal domain of MdmX and the crystal structure of the N-terminal domain of Mdm2 in complex with nutlin-3a (an Mdm2-specific inhibitor). The current work establishes a small molecule therapeutic candidate that targets cancers overexpressing Mdm2 and/or MdmX.

Vicinal diamination of alkenes under Rh-catalysis

The synthesis of 1,2-diamines has been achieved through a single-step, tandem sequence involving Rh-catalyzed aziridination followed by NaI-promoted rearrangement to an isomeric cyclic sulfamide. Facile ring opening of these products in hot water and pyridine affords differentially protected vicinal diamines. Demonstration of the utility of this method for the syntheses of (±)-enduracididine and (±)-allo-enduracididine is highlighted.

Organocatalytic, diastereo- and enantioselective synthesis of nonsymmetric cis-stilbene diamines: a platform for the preparation of single-enantiomer cis-imidazolines for protein-protein inhibition

The finding by scientists at Hoffmann-La Roche that cis-imidazolines could disrupt the protein–protein interaction between p53 and MDM2, thereby inducing apoptosis in cancer cells, raised considerable interest in this scaffold over the past decade. Initial routes to these small molecules (i.e., Nutlin-3) provided only the racemic form, with enantiomers being enriched by chromatographic separation using high-pressure liquid chromatography (HPLC) and a chiral stationary phase. Reported here is the first application of an enantioselective aza-Henry approach to nonsymmetric cis-stilbene diamines and cis-imidazolines. Two novel mono(amidine) organocatalysts (MAM) were discovered to provide high levels of enantioselection (>95% ee) across a broad range of substrate combinations. Furthermore, the versatility of the aza-Henry strategy for preparing nonsymmetric cis-imidazolines is illustrated by a comparison of the roles of aryl nitromethane and aryl aldimine in the key step, which revealed unique substrate electronic effects providing direction for aza-Henry substrate–catalyst matching. This method was used to prepare highly substituted cis-4,5-diaryl imidazolines that project unique aromatic rings, and these were evaluated for MDM2-p53 inhibition in a fluorescence polarization assay. The diversification of access to cis-stilbene diamine-derived imidazolines provided by this platform should streamline their further development as chemical tools for disrupting protein–protein interactions.

Silyl imine electrophiles in enantioselective catalysis: a Rosetta Stone for peptide homologation, enabling diverse N-protected aryl glycines from aldehydes in three steps

We report that N-(trimethylsilyl)imines serve in the Bis(AMidine)-catalyzed addition of bromonitromethane with a high degree of enantioselection. This allows for the production of a range of protected α-bromo nitroalkane donors (including Fmoc) for use in Umpolung Amide Synthesis (UmAS). Hence, peptide homologation with nonnatural aryl glycine amino acids is achieved in three steps from aromatic aldehydes, which are plentiful and inexpensive. Epimerization during the homologation step is circumvented by avoiding an α-amino acid intermediate.

On the origin of the stereoselective affinity of Nutlin-3 geometrical isomers for the MDM2 protein

The stereoselective affinity of small-molecule binding to proteins is typically broadly explained in terms of the thermodynamics of the final bound complex. Using Brownian dynamics simulations, we show that the preferential binding of the MDM2 protein to the geometrical isomers of Nutlin-3, an effective anticancer lead that works by inhibiting the interaction between the proteins p53 and MDM2, can be explained by kinetic arguments related to the formation of the MDM2:Nutlin-3 encounter complex. This is a diffusively bound state that forms prior to the final bound complex. We find that the MDM2 protein stereoselectivity for the Nutlin-3a enantiomer stems largely from the destabilization of the encounter complex of its mirror image enantiomer Nutlin-3b, by the K70 residue that is located away from the binding site. On the other hand, the trans-Nutlin-3a diastereoisomer exhibits a shorter residence time in the vicinity of MDM2 compared with Nutlin-3a due to destabilization of its encounter complex by the collective interaction of pairs of charged residues on either side of the binding site: Glu25 and Lys51 on one side, and Lys94 and Arg97 on the other side. This destabilization is largely due to the electrostatic potential of the trans-Nutlin-3a isomer being largely positive over extended continuous regions around its structure, which are otherwise well-identified into positive and negative regions in the case of the Nutlin-3a isomer. Such rich insight into the binding processes underlying biological selectivity complements the static view derived from the traditional thermodynamic analysis of the final bound complex. This approach, based on an explicit consideration of the dynamics of molecular association, suggests new avenues for kinetics-based anticancer drug development and discovery.

Bifunctional iminophosphorane organocatalysts for enantioselective synthesis: application to the ketimine nitro-Mannich reaction

The design, synthesis, and development of a new class of modular, strongly basic, and tunable bifunctional Brønsted base/H-bond-donor organocatalysts are reported. These catalysts incorporate a triaryliminophosphorane as the Brønsted basic moiety and are readily synthesized via a last step Staudinger reaction of a chiral organoazide and a triarylphosphine. Their application to the first general enantioselective organocatalytic nitro-Mannich reaction of nitromethane to unactivated ketone-derived imines allows the enantioselective construction of β-nitroamines possessing a fully substituted carbon atom. The reaction is amenable to multigram scale-up, and the products are useful for the synthesis of enantiopure 1,2-diamine and α-amino acid derivatives.

Preparation of (-)-Nutlin-3 using enantioselective organocatalysis at decagram scale

Chiral nonracemic cis-4,5-bis(aryl)imidazolines have emerged as a powerful platform for the development of cancer chemotherapeutics, stimulated by the Hoffmann-La Roche discovery that Nutlin-3 can restore apoptosis in cells with wild-type p53. The lack of efficient methods for the enantioselective synthesis of cis-imidazolines, however, has limited their more general use. Our disclosure of the first enantioselective synthesis of (-)-Nutlin-3 provided a basis to prepare larger amounts of this tool used widely in cancer biology. Key to the decagram-scale synthesis described here was the discovery of a novel bis(amidine) organocatalyst that provides high enantioselectivity at warmer reaction temperature (-20 °C) and low catalyst loadings. Further refinements to the procedure led to the synthesis of (-)-Nutlin-3 in a 17 g batch and elimination of all but three chromatographic purifications.

Synthesis of the reported structure of piperazirum using a nitro-Mannich reaction as the key stereochemical determining step

Piperazirum, isolated from Arum palaestinum Boiss, was originally assigned as r-3,c-5-diisobutyl-c-6-isopropylpiperazin-2-one. The reported structure was synthesised diastereoselectively using a key nitro-Mannich reaction to set up the C5/C6 relative stereochemistry. The structure was unambiguously assigned by single crystal X-ray diffraction but the spectroscopic data did not match those reported for the natural product. The structure of the natural product must therefore be revised.

Minimizing the amount of nitromethane in palladium-catalyzed cross-coupling with aryl halides

A method for the formation of arylnitromethanes is described that employs readily available aryl halides or triflates and small amounts of nitromethane in a dioxane solvent, thereby reducing the hazards associated with this reagent. Specifically, 2-10 equiv (1-5% v/v) of nitromethane can be employed in comparison to prior work that used nitromethane as solvent (185 equiv). The present transformation provides high yields at relatively low temperatures and tolerates an array of functionality, including heterocycles and substantial steric encumbrance.

P53 mdm2 inhibitors

The protein-protein interaction (PPI) between p53 and its negative regulator MDM2 comprises one of the most important and intensely studied PPI's involved in preventing the initiation of cancer. The interaction between p53 and MDM2 is conformation-based and is tightly regulated on multiple levels. Due to the Angstrom level structural insight there is a reasonable understanding of the structural requirements needed for a molecule to bind to MDM2 and successfully inhibit the p53/MDM2 interaction. The current review summarizes the binding characteristics of the different disclosed small molecules for inhibition of MDM2 with a co-crystal structure. Synthetic access to these compounds as well as their derivatives are described in detail.

Cu-catalyzed selective mono-N-pyridylation: direct access to 2-aminoDMAP/sulfonamides as bifunctional organocatalysts

Direct and selective mono-N-pyridylation of trans-(R,R)-cyclohexane-1,2-diamine is described here. Facile preparation of a novel chiral 2-aminoDMAP core catalaphore via Cu catalysis has led to the development of various sulfonamide/2-aminoDMAPs as bifunctional acid/base organocatalysts (most in two steps overall), which have been shown to very effectively promote asymmetric conjugate addition of acetylacetone to trans-β-nitroolefins with good to excellent yields (87-93%) and enantioselectivites (up to 99%).

Organocatalytic, enantioselective synthesis of VNI: a robust therapeutic development platform for Chagas, a neglected tropical disease

VNI is a potent inhibitor of CYP51 and was recently shown to achieve a parasitological cure of mice infected with T. cruzi in both acute and chronic stages of infection. T. cruzi is the causative parasite of Chagas disease, a neglected tropical disease. The first enantioselective chemical synthesis of VNI (at a materials cost of less than $0.10/mg) is described. Furthermore, the key enantioselective step is performed at the 10 g scale.

Palladium-catalyzed nitromethylation of aryl halides: an orthogonal formylation equivalent

An efficient cross-coupling reaction of aryl halides and nitromethane was developed with the use of parallel microscale experimentation. The arylnitromethane products are precursors for numerous useful synthetic products. An efficient method for their direct conversion to the corresponding oximes and aldehydes in a one-pot operation has been discovered. The process exploits inexpensive nitromethane as a carbonyl equivalent, providing a mild and convenient formylation method that is compatible with many functional groups.

Methods for direct alkene diamination, new & old

The 1,2-diamine moiety is a ubiquitous structural motif present in a wealth of natural products, including non-proteinogenic amino acids and numerous alkaloids, as well as in pharmaceutical agents, chiral ligands and organic reagents. The biological activity associated with many of these systems and their chemical utility in general has ensured that the development of methods for their preparation is of critical importance. While a wide range of strategies for the preparation of 1,2-diamines have been established, the diamination of alkenes offers a particularly direct and efficient means of accessing these systems. The purpose of this review is to provide an overview of all methods of direct alkene diamination, metal-mediated or otherwise.

Chiral proton catalysis of secondary nitroalkane additions to azomethine: synthesis of a potent GlyT1 inhibitor

The first enantioselective synthesis of a potent GlyT1 inhibitor is described. A 3-nitroazetidine donor is used in an enantioselective aza-Henry reaction catalyzed by a bis(amidine)-triflic acid salt organocatalyst, delivering the key intermediate with 92% ee. This adduct is reductively denitrated and converted to the target through a short sequence, thereby allowing assignment of the absolute configuration of the more potent enantiomer.

Stereocontrolled synthesis of vicinal diamines by organocatalytic asymmetric Mannich reaction of N-protected aminoacetaldehydes: formal synthesis of (-)-agelastatin A

The 1,2-diamine (vicinal diamine) motif is present in a number of natural products with interesting biological activity and in many chiral molecular catalysts. The efficient and stereocontrolled synthesis of enantioenriched vicinal diamines is still a challenge to modern chemical methodology. We report here both syn- and anti-selective asymmetric direct Mannich reactions of N-protected aminoacetaldehydes with N-Boc-protected imines catalyzed by proline and the axially chiral amino sulfonamide (S)-3. This organocatalytic process represents the first example of a Mannich reaction using Z- or Boc-protected aminoacetaldehyde as a new entry of α-nitrogen functionalized aldehyde nucleophile in enamine catalysis. The obtained optically active vicinal diamines are useful chiral synthons as exemplified by the formal synthesis of (-)-agelastatin A.

Achiral counterion control of enantioselectivity in a Brønsted acid-catalyzed iodolactonization

Highly enantioselective halolactonizations have been developed that employ a chiral proton catalyst-N-iodosuccinimide (NIS) reagent system in which the Brønsted acid is used at catalyst loadings as low as 1 mol %. An approach that modulates the achiral counterion (equimolar to the neutral chiral ligand-proton complex present at low catalyst loadings) to optimize the enantioselection is documented for the first time in this transformation. In this way, unsaturated carboxylic acids are converted to γ-lactones in high yields (up to 98% ee) using commercially available NIS.