Cinchona Alkaloid-derived Primary Amine Research Articles

4-Plex Chemical Labeling Strategy Based on Cinchona Alkaloid-Derived Primary Amines for the Analysis of Chiral Carboxylic Acids by Liquid Chromatography-Mass Spectrometry.

Chiral carboxylic acids play important roles in energy metabolism and signal transduction in the human body. These enantiomers usually possess different bioactivities and are also associated with the development of some diseases. Therefore, simultaneous determination of multiple chiral carboxylic acids is vital for study of the pathogenesis of related diseases. However, it is still challenging to simultaneously detect the enantiomers of multiple chiral carboxylic acids in biological samples. Here, we developed a novel 4-plex chemical labeling strategy based on 4 analogues of cinchona alkaloid-derived primary amines (CAPAs) for simultaneous determination of 16 enantiomers of 8 chiral carboxylic acids by liquid chromatography-mass spectrometry (LC-MS). To achieve high-throughput analysis, one CAPA analogue was used to label chiral carboxylic acid standards and served as internal standards (ISs), while the other 3 CAPA analogues were used to label endogenous chiral carboxylic acids in 3 different biological samples. After CAPAs labeling, the 16 chiral carboxylic acid enantiomers could be detected by LC-MS, and their detection sensitivity was greatly enhanced by up to 3 orders of magnitude compared to intact analytes. Further, the developed method for the determination of 16 chiral carboxylic acid enantiomers was validated in human serums and mammalian cells. Finally, the proposed method was applied to the determination of chiral carboxylic acids in the serum samples from type 2 diabetes mellitus (T2DM) and colorectal cancer (CRC) patients. We found that 5 chiral carboxylic acid enantiomers in T2DM serum samples and 4 chiral carboxylic acid enantiomers in CRC serum samples exhibited significant change compared to the healthy control (HC).

Asymmetric Mannich Reaction of Aryl Methyl Ketones with Cyclic Imines Benzo[e][1,2,3]oxathiazine 2,2-Dioxides Catalyzed by Cinchona Alkaloid-based Primary Amines.

Aryl ketones represent problematic substrates for asymmetric Mannich reactions due to a large steric hindrance exhibited by such compound species. A highly enantioselective direct Mannich reaction of aryl methyl ketones with cyclic imine benzo[e][1,2,3]oxathiazine 2,2-dioxides could be successfully carried out utilizing a combination of cinchona alkaloid-derived primary amines with trifluoroacetic acid (TFA); the primary amines feature a superior catalytic efficacy over secondary amines with a variety of sterically hindered carbonyl compounds as substrates. The reaction proceeded well with various cyclic imines in 89-97 % ee and with various aryl methyl ketones in 85-98 % ee. Moreover, the aryl carbonyl of a Mannich product could be transformed to ketoxime, which further undergoes a Beckmann rearrangement to produce an amide compound while maintaining enantioselectivity.

ChemInform Abstract: Theory and Modeling of Asymmetric Catalytic Reactions

AbstractReview: 70 refs.

Theory and Modeling of Asymmetric Catalytic Reactions.

Modern density functional theory and powerful contemporary computers have made it possible to explore complex reactions of value in organic synthesis. We describe recent explorations of mechanisms and origins of stereoselectivities with density functional theory calculations. The specific functionals and basis sets that are routinely used in computational studies of stereoselectivities of organic and organometallic reactions in our group are described, followed by our recent studies that uncovered the origins of stereocontrol in reactions catalyzed by (1) vicinal diamines, including cinchona alkaloid-derived primary amines, (2) vicinal amidophosphines, and (3) organo-transition-metal complexes. Two common cyclic models account for the stereoselectivity of aldol reactions of metal enolates (Zimmerman-Traxler) or those catalyzed by the organocatalyst proline (Houk-List). Three other models were derived from computational studies described in this Account. Cinchona alkaloid-derived primary amines and other vicinal diamines are venerable asymmetric organocatalysts. For α-fluorinations and a variety of aldol reactions, vicinal diamines form enamines at one terminal amine and activate electrophilically with NH(+) or NF(+) at the other. We found that the stereocontrolling transition states are cyclic and that their conformational preferences are responsible for the observed stereoselectivity. In fluorinations, the chair seven-membered cyclic transition states is highly favored, just as the Zimmerman-Traxler chair six-membered aldol transition state controls stereoselectivity. In aldol reactions with vicinal diamine catalysts, the crown transition states are favored, both in the prototype and in an experimental example, shown in the graphic. We found that low-energy conformations of cyclic transition states occur and control stereoselectivities in these reactions. Another class of bifunctional organocatalysts, the vicinal amidophosphines, catalyzes the (3 + 2) annulation reaction of allenes with activated olefins. Stereocontrol here is due to an intermolecular hydrogen bond that activates the electrophilic partner in this reaction. We have also studied complex organometallic catalysts. Krische's ruthenium-catalyzed asymmetric hydrohydroxyalkylation of butadiene involves two chiral ligands at Ru, a chiral diphosphine and a chiral phosphate. The size of this combination strains the limits of modern computations with over 160 atoms, multiple significant steps, and a variety of ligand coordinations and conformations possible. We found that carbon-carbon bond formation occurs via a chair Zimmerman-Traxler-type transition structure and that a formyl CH···O hydrogen bond from aldehyde CH to phosphate oxygen, as well as steric interactions of the two chiral ligands, control the stereoselectivity.

Origins of stereoselectivity in intramolecular aldol reactions catalyzed by cinchona amines.

The intramolecular aldol condensation of 4-substituted heptane-2,6-diones leads to chiral cyclohexenones. The origins of the enantioselectivities of this reaction, disclosed by List et al. using a cinchona alkaloid-derived primary amine (cinchona amine) organocatalyst, have been determined with dispersion-corrected density functional theory (DFT). The stereocontrol hinges on the chair preference of the substrate-enamine intermediate and the conformational preferences of a hydrogen-bonded nine-membered aldol transition state containing eight heavy atoms. The conformations of the hydrogen-bonded ring in the various stereoisomeric transition structures have been analyzed in detail and shown to closely resemble the conformers of cyclooctane. A model of stereoselectivity is proposed for the cinchona amine catalysis of this reaction. The inclusion of Grimme's dispersion corrections in the DFT calculations (B3LYP-D3(BJ)) substantially improves the agreement of the computed energetics and experiment, attesting to the importance of dispersion effects in stereoselectivity.

ChemInform Abstract: How Cinchona Alkaloid‐Derived Primary Amines Control Asymmetric Electrophilic Fluorination of Cyclic Ketones.

The origin of selectivity in the α-fluorination of cyclic ketones catalyzed by cinchona alkaloid-derived primary amines is determined with density functional calculations. The chair preference of a seven-membered ring at the fluorine transfer transition state is key in determining the sense and level of enantiofacial selectivity.

Synthesis of highly decorated chiral 2-nitro-cyclohexane carboxylic esters through microwave-assisted organocatalyzed cascade reactions

Starting from (E)-β-substituted-β-nitroacrylates and α,β-unsaturated ketones, a stereoselective organocatalyzed one-pot methodology allowed to synthesize highly decorated chiral 2-nitro-cyclohexane carboxylic esters. The reaction is promoted by Cinchona alkaloid-derived primary amines in the presence of an acidic co-catalyst and affords two diastereoisomers, in good yields and high enantiomeric excess (often higher than 90% ee). By replacing conventional heating with microwave irradiation, cleaner reactions in shortened times (from 48h to 30min) were obtained, with improved dr (80:20) and high ee (up to 94%). The application of microwave technology to this organocatalytic methodology allowed also employing C1 substituted enones, leading to cyclohexanones with four contiguous stereocenters in two isomers only, and up to 99% enantioselectivity.

How cinchona alkaloid-derived primary amines control asymmetric electrophilic fluorination of cyclic ketones.

The origin of selectivity in the α-fluorination of cyclic ketones catalyzed by cinchona alkaloid-derived primary amines is determined with density functional calculations. The chair preference of a seven-membered ring at the fluorine transfer transition state is key in determining the sense and level of enantiofacial selectivity.

Theoretical investigation on mechanism of asymmetric Michael addition of trans-1-nitro-2-phenylethylene to 2-methylpropionaldehyde catalyzed by a Cinchona alkaloid-derived primary amine

Using cinchona alkaloid-derived primary amine as catalyst and benzoic acid as co-catalyst, Michael-type addition reactions between enolizable carbonyl compounds and nitroalkenes have been extensively studied; however, our understanding of the mechanism is far from complete. In this paper, a theoretical study is presented for the Michael addition reaction between trans-1-nitro-2-phenylethylene and 2-methylpropionaldehyde catalyzed by 9-epi-QDA and benzoic acid. By performing DFT and ab initio calculations, we have identified a detailed mechanism. The calculations indicated that four continuous steps are involved in the overall reaction: (1) the formation of an iminium intermediate, (2) an addition reaction between the iminium and trans-1-nitro-2-phenylethylene, (3) the proton transfer process, and (4) hydrolysis and regeneration of the catalyst. The rate-determining step is the second proton transfer from the amine group to β-carbon of trans-1-nitro-2-phenylethylene, and the enantioselectivity is also controlled by this step. The calculated results provide a general model that explains the mechanism and enantioselectivity of the title reaction.

ChemInform Abstract: Molecular Assembly of an Achiral Phosphine and a Chiral Primary Amine: A Highly Efficient Supramolecular Catalyst for the Enantioselective Michael Reaction of Aldehydes with Maleimides.

A combined catalyst system of a cinchonidine-derived primary amine and triphenylphosphine (CDNH 2 /PPh 3 ) exhibited high catalytic performance in the Michael reaction of aldehydes with maleimides, thereby affording the corresponding functionalized aldehydes in excellent yields (up to 99%) and enantioselectivities (>99% ee). More interestingly, the significance of the phosphine in enhancing the enantioselectivities in the chiral-primary-amine-catalyzed Michael reaction was revealed. Furthermore, we explored the origin of the reaction mechanism in the Michael addition promoted by the dual organocatalytic system. On the basis of experimental results and spectroscopic analysis, such as UV/Vis, fluorescence emission (FL), NMR, and circular dichroism (CD) spectroscopy, as well as ESI-MS, we found that the molecular assembly of phosphine and primary amine played a crucial role in this enantioselective reaction, in which a possible supramolecular complex was formed as an effective chiral catalyst through noncovalent molecular interactions of a cinchona alkaloid-derived primary amine with triphenylphosphine.

Asymmetric Organocatalytic Michael Addition of Pyrroles to Enones by Cinchona Alkaloid-Derived Primary Amines

The enantioselective synthesis of 2-alkylated pyrroles via Michael addition of pyrroles to α,β-unsaturated ketones employing cinchona alkaloid-derived primary amines as organocatalysts is described. Good to excellent yields (78–99%) and good to very good enantioselectivities (75–93% ee) are obtained. With this protocol highly enantioenriched C-alkylated pyrroles can be synthesized easily, thus facilitating their possible application in medicinal chemistry.

The Cinchona Primary Amine-Catalyzed Asymmetric Epoxidation and Hydroperoxidation of α,β-Unsaturated Carbonyl Compounds with Hydrogen Peroxide

Using cinchona alkaloid-derived primary amines as catalysts and aqueous hydrogen peroxide as the oxidant, we have developed highly enantioselective Weitz-Scheffer-type epoxidation and hydroperoxidation reactions of α,β-unsaturated carbonyl compounds (up to 99.5:0.5 er). In this article, we present our full studies on this family of reactions, employing acyclic enones, 5-15-membered cyclic enones, and α-branched enals as substrates. In addition to an expanded scope, synthetic applications of the products are presented. We also report detailed mechanistic investigations of the catalytic intermediates, structure-activity relationships of the cinchona amine catalyst, and rationalization of the absolute stereoselectivity by NMR spectroscopic studies and DFT calculations.

Molecular Assembly of an Achiral Phosphine and a Chiral Primary Amine: A Highly Efficient Supramolecular Catalyst for the EnantioselectiveMichael Reaction of Aldehydes with Maleimides

A combined catalyst system of a cinchonidine-derived primary amine and triphenylphosphine (CD-NH2 /PPh3 ) exhibited high catalytic performance in the Michael reaction of aldehydes with maleimides, thereby affording the corresponding functionalized aldehydes in excellent yields (up to 99 %) and enantioselectivities (>99 % ee). More interestingly, the significance of the phosphine in enhancing the enantioselectivities in the chiral-primary-amine-catalyzed Michael reaction was revealed. Furthermore, we explored the origin of the reaction mechanism in the Michael addition promoted by the dual organocatalytic system. On the basis of experimental results and spectroscopic analysis, such as UV/Vis, fluorescence emission (FL), NMR, and circular dichroism (CD) spectroscopy, as well as ESI-MS, we found that the molecular assembly of phosphine and primary amine played a crucial role in this enantioselective reaction, in which a possible supramolecular complex was formed as an effective chiral catalyst through noncovalent molecular interactions of a cinchona alkaloid-derived primary amine with triphenylphosphine.

Organocatalytic asymmetric α-benzoyloxylation of α-branched aldehydes and enals: a useful approach to oxygenated quaternary stereocenters

Direct asymmetric α-benzoyloxylation of α-branched aldehydes and α-branched enals via enamine and dienamine catalysis was used to construct quaternary oxygenated stereocenters with good yields and moderate to good enantioselectivity. This method uses an inexpensive and readily available cinchona alkaloid-derived primary amine as the catalyst, benzoyl peroxide as the oxygen source, and stoichiometric amounts of the aldehyde substrates, providing simple metal-free access to valuable protected 2-hydroxyaldehyde derivatives.

Organocatalyzed enantioselective aldol reaction of 1 H-pyrrole-2,3-diones

The enantioselective cross aldol reaction of 1-benzyl 4,5-dioxo-2-aryl-4,5-dihydro-1 H-pyrrole-3-carboxylates and ketones was studied with proline derivatives or cinchona alkaloid-derived primary amines as the catalysts for the first time. trans-4-Benzoyloxy- l-proline ( 15) was found to be the best catalyst for acyclic ketones. For cyclohexanone, the best results were achieved with 9-deoxy-9- epi-aminoquinine ( 18) as the catalyst in the presence of racemic 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate ( 19) as the cocatalyst. Using these protocols, 3-alkyl-3-hydroxy-1 H-pyrrol-2(3 H)-one derivatives were obtained in excellent yields and good to high ee values (up to 94% ee).

ChemInform Abstract: Recent Advances in Asymmetric Catalysis with Cinchona Alkaloid‐Based Primary Amines.

AbstractReview: 86 refs.

Recent advances in asymmetric catalysis with cinchona alkaloid-based primary amines

Six years have passed since renewed attention was paid to primary amines as potential organocatalysts in 2004. Numerous high quality studies in this field have provided chemists with valuable insights into the unique properties of chiral primary aminocatalysis. Among the diverse catalysts, natural cinchona alkaloid-derived catalysts have been widely regarded as a branch with high efficiency. This review examines the literature published between 2008 and late 2010, concerning cinchona alkaloid-derived primary amine catalysis.

Combined organo- and gold-catalyzed enantioselective synthesis of bicyclic enones

By combining organocatalysis with gold catalysis highly enantioenriched bicyclic enones are available via an operationally simple one-pot procedure. Iminium-ion activation by cinchona alkaloid-derived primary amine catalysts induces the Michael addition of propargylated malononitriles and cyanoacetates to α,β-unsaturated ketones. The resulting intermediates undergo an exo-dig cyclization, forming a new C–C bond followed by double-bond isomerization to give highly functionalized bicyclic enones in good yields and high enantioselectivities.

Asymmetric organocatalytic Michael addition of ketones to vinyl sulfone

Highly enantioselective organocatalytic Michael addition of ketones to vinyl sulfone catalyzed by a cinchona alkaloid-derived primary amine is reported for the first time; the described synthetic methodology was applied to the synthesis of sodium cyclamate.