Chiral Β-amino Acid Derivatives Research Articles

Enantioselective Access to β-Amino Carbonyls via Ni-Catalyzed Formal Olefin Hydroamidation.

We herein describe a Ni-catalyzed formal hydroamidation of readily available α,β-unsaturated carbonyl compounds to afford valuable chiral β-amino acid derivatives (up to >99:1 e.r.) using dioxazolones as a robust amino source. A wide range of alkyl-substituted olefins conjugated to esters, amides, thioesters, and ketones were successfully amidated at the β-position with excellent enantioselectivity for the first time. Combined experimental and computational mechanistic studies supported our working hypothesis that this unconventional β-amidation of unsaturated carbonyl substrates can be attributed to the polar-matched migratory olefin insertion of an (amido)(Cl)NiII intermediate, in situ generated from the dioxazolone precursor.

Organocatalytic Synthesis of Highly Functionalized Heterocycles by Enantioselective aza-Morita-Baylis-Hillman-Type Domino Reactions.

Organocatalytic enantioselective domino reactions are an extremely attractive methodology, as their use enables the construction of complex chiral skeletons from readily available starting materials in two or more steps by a single operation under mild reaction conditions. Thus, these reactions can save both the quantity of chemicals and length of time typically required for the isolation and/or purification of synthetic intermediates. Additionally, no metal contamination of the products occurs, given that organocatalysts include no expensive or toxic metals. The aza-Morita-Baylis-Hillman (aza-MBH) reaction is an atom-economical carbon-carbon bond-forming reaction between α,β-unsaturated carbonyl compounds and imines mediated by Lewis base (LB) catalysts, such as nucleophilic phosphines and amines. aza-MBH products are functionalized chiral β-amino acid derivatives that are highly valuable as pharmaceutical raw materials. Although various enantioselective aza-MBH processes have been investigated, very few studies of aza-MBH-type domino reactions have been reported due to the complexity of the aza-MBH process, which involves a Michael/Mannich/H-transfer/β-elimination sequence. Accordingly, in this review article, our recent efforts in the development of enantioselective domino reactions initiated by MBH processes are described. In the domino reactions, chiral organocatalysts bearing Brønsted acid (BA) and/or LB units impart synergistic activation to substrates, leading to the easy synthesis of highly functionalized heterocycles (some of which have tetrasubstituted and/or quaternary carbon stereocenters) in high yield and enantioselectivity.

Nickel-Catalyzed Enantioselective Hydrogenation of β-(Acylamino)acrylates: Synthesis of Chiral β-Amino Acid Derivatives.

The nickel-catalyzed asymmetric hydrogenation of β-(acylamino)acrylates has been developed, affording chiral β-amino acid derivatives with excellent yields (95-99% yield) and enantioselectivities (97-99% ee). With the Ni-Binapine system, high enantioselectivities (98-99% ee) have also been obtained in the hydrogenation of Z/E isomeric mixtures of β-alkyl and β-aryl β-(acylamino)acrylates. The synthesis of chiral β-amino acid derivatives on a gram scale has also been achieved with 0.2 mol % catalyst loading.

Stereoselective synthesis of perillaldehyde-based chiral β-amino acid derivatives through conjugate addition of lithium amides.

The Michael addition of dibenzylamine to (+)-tert-butyl perillate (3) and to (+)-tert-butyl phellandrate (6), derived from (S)-(−)-perillaldehyde (1), resulted in diastereomeric β-amino esters 7A–D in a moderately stereospecific reaction in a ratio of 76:17:6:1. After separation of the diastereoisomers, the major product, cis isomer 7A, was quantitatively isomerized to the minor component, trans-amino ester 7D. All four isomers were transformed to the corresponding β-amino acids 10A–D, which are promising building blocks for the synthesis of β-peptides and 1,3-heterocycles in three steps. The steric effects of the isopropyl group at position 4 and of the α-methyl substituent of (R)-N-benzyl-N-α-methylbenzylamine on the reactivity were also studied and, upon application of a chiral amine, excellent stereoselectivity of the conjugate addition was observed. Amino ester 11 was obtained as a single product and transformed to the corresponding amino acids 10A and 10D in good yields on the gram scale.

One-pot synthesis of novel chiral β-amino acid derivatives by enantioselective Mannich reactions catalyzed by squaramide cinchona alkaloids.

An efficient one-pot synthesis of novel β-amino acid derivatives containing a thiadiazole moiety was developed using a chiral squaramide cinchona alkaloid as organocatalyst. The reactions afforded chiral β-amino acid derivatives in moderate yields and with moderate to excellent enantioselectivities. The present study demonstrated for the first time the use of a Mannich reaction catalyzed by a chiral bifunctional organocatalyst for the one-pot synthesis of novel β-amino acid derivatives bearing a 1,3,4-thiadiazole moiety on nitrogen.

Catalytic Synthesis of Optically Active β-Amino Acid Derivatives

In continuation to our earlier reviews on organocatalysis, a systematic approach for the synthesis of chiral β-amino acid derivatives in the presence of mainly organocatalysts and transition metal catalysts are described. Asymmetric Mannich reactions catalyzed by proline and bifunctional organocatalysts are explained, whereas metal catalysis based on hydrogenation, Mannich and conjugate additions are elaborated. The resulting β-amino carbonyl moieties are essential structural units of many natural products and are important chiral building blocks for the synthesis of nitrogen-containing bioactive molecules. Keywords: Bifunctional organocatalysts, chiral β-amino acids, conjugate addition, hydrogenation, mannich reaction, proline, transition metal catalysts, transition metal, β-peptides, natural products, pharmaceuticals

Synthesis of chiral β-amino acid derivatives by asymmetric hydrosilylation with an imidazole derived organocatalyst

The organocatalysed asymmetric hydrosilylation of a number of N-aryl and alkyl β-substituted enamino esters proceeds in generally good yield and enantioselectivity. Crucial to obtaining high yield and selectivity was the addition of benzoic acid as an additive and under these conditions, both N-alkyl and N-aryl substituents were well tolerated. β-Aryl and alkyl substituents were evaluated and a model proposed to account for the experimental observations based upon enamine tautomerisation and conformational preferences of the reactive ketimine intermediate.

Monoterpene-based chiral β-amino acid derivatives prepared from natural sources: syntheses and applications

Natural monoterpenes have proved to be good starting materials for the synthesis of β-amino acid derivatives. In the past decade, a number of well-known synthetic procedures have been applied for the preparation of monoterpene-based β-amino acid derivatives, e.g. from β-lactams via the 1,2-dipolar cycloaddition of chlorosulfonyl isocyanate to commercial or readily available monoterpenes [e.g. (+)- and (-)-α- or δ-pinene, (+)-3- and 2-carene, (+)- and (-)-apopinene], the conjugate addition of amides to monoterpene-based α,β-unsaturated esters or the transformations of (-)-cis-pinonoic acid prepared by the oxidative cleavage of (+)- and (-)-verbenone. β-Amino acid derivatives are excellent building blocks for versatile transformations, e.g. multicomponent reactions resulting in β-lactams, syntheses of 1,3-heterocycles and diaminopyrimidine derivatives or the formation of peptides containing an H12 helix. 1,3-Amino alcohol derivatives prepared from β-amino esters have been applied as chiral catalysts in enantioselective transformations. Several of these compounds are of noteworthy pharmacological importance, such as tyrosine kinase Axl inhibitor diaminopyrimidine-coupled β-aminocarboxamides, MDR inhibitor thiourea derivatives of β-amino esters or 2-imino-1,3-oxazines, which exhibit marked growth inhibitory activity on multiple cancer cell lines. The present review summarizes recent developments relating to the syntheses, applications and pharmaceutical importance of monoterpene-based β-amino acids and their derivatives.

Asymmetric Synthesis of New Chiral β-Amino Acid Derivatives by Mannich-type Reactions of Chiral N-Sulfinyl Imidates with N-Tosyl Aldimines

New chiral beta-(sulfonylamino)sulfinylimidates are synthesized in high overall yield and excellent diastereomeric excess via highly anti-selective Mannich-type reactions of chiral N-tert-butanesulfinyl imidates with N-tosyl aldimines. Deprotection of the beta-(sulfonylamino)sulfinylimidates gave access to enantiopure imidate hydrochlorides in high yields, as useful intermediates for an easy transformation to new chiral beta-sulfonylamino amides upon simple heating in chloroform. Hydrolysis of the imidate hydrochlorides afforded the corresponding chiral beta-sulfonylamino esters with >98% ee as new chiral beta-amino acid derivatives.

Combinatorial approach to the asymmetric hydrogenation of β-acylamino acrylates: use of mixtures of chiral monodentate P-ligands

The previously proposed concept of using mixtures of two different chiral monodentate P-ligands has been extended to the asymmetric Rh-catalyzed hydrogenation of β-acylamino acrylates with formation of chiral β-amino acid derivatives. Mixtures of BINOL-derived phosphites and phosphonites are particularly effective ( ee=94–99% for five different substrates).

Highly diastereoselective heterogeneously catalyzed hydrogenation of enamines for the synthesis of chiral beta-amino acid derivatives.

Pure (Z)-enamines readily prepared from beta-ketoesters and amides using (S)-phenylglycine amide were hydrogenated with very high diastereoselectivities (up to 200:1) using heterogeneous catalysis. Hydrogenolytic cleavage of the (S)-phenylglycine amide afforded the corresponding chiral beta-aminoesters and amides. The high geometrical purity of the (Z)-enamine and a simple activation procedure for the PtO2 catalyst are essential in achieving high selectivity.

Chiral β-Amino Acid Derivatives via Asymmetric Hydrogenation

This contribution gives an overview of the synthesis of chiral β-amino acids via asymmetric hydrogenation of the corresponding dehydroamino derivatives. Literature results are discussed regarding substrate synthesis and catalyst performance and how it is affected by substrate and catalyst structure as well as experimental parameters. A tentative mechanistic concept for the hydrogenation step is also presented.

Highly Efficient Synthesis of Chiral β‐Amino Acid Derivatives via Asymmetric Hydrogenation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly efficient synthesis of chiral beta-amino acid derivatives via asymmetric hydrogenation.

The Rh-TangPhos complex is an efficient hydrogenation catalyst for making chiral beta-amino acid derivatives. With the Rh-TangPhos system, high enantioselectivities (up to 99.6%) and turnover numbers have been obtained in the hydrogenation of E/Z isomeric mixtures of both beta-alkyl and beta-aryl beta-(acylamino)acrylates. [reaction: see text]

Synthesis and Crystal Structure of N-[(15,4R)-2-Oxo-pinanyl]-β-alanine Methylester

Abstract The title compound, N-[(lS,4R)-2-oxo-pinanyl]-β-alanine methylester, is an important starting material for the electrochemical preparation of chiral amidoalkylation reagents in the synthesis of chiral β-substituted β-amino acid derivatives. The investigation of its crystal structure reveals an arrangement of the carbonyl group and the amine function, which is influenced by a hydrogen bonding interaction. This conformation makes the molecule especially appropriate for further synthetical modification

Dynamic Kinetic Resolution Utilizing 2-Oxoimidazolidine-4-carboxylate as a Chiral Auxiliary: Stereoselective Alkylation of α-Bromo Amides with Malonic Ester Enolates

Stereoselective carbon−carbon bond formation by dynamic kinetic resolution using tert-butyl (4S)-1-methyl-2-oxoimidazolidine-4-carboxylate (1) as a chiral auxiliary was developed. Reaction of a diastereomeric mixture of tert-butyl (4S)-3-[(2RS)-2-bromoacyl]-1-methyl-2-oxoimidazolidine-4-carboxylates (2) with a malonic ester enolate in HMPA predominantly afforded tert-butyl (4S)-3-[(2R)-2-alkyl-3,3-bis(alkoxycarbonyl)propionyl]-1-methyl-2-oxoimidazolidine-4-carboxylate [(S,R)-8] in good yields. The stereoselectivity of this reaction was in accordance with our working hypothesis based on the conformational analysis of 2 and elucidated the unique characteristics of 1 as a novel chiral auxiliary for dynamic kinetic resolution. The alkylated products (S,R)-8e,j,k were easily converted to chiral α-alkyl succinic acid derivatives and chiral β-amino acid derivatives, both of which have been known as key building blocks for the syntheses of a variety of biologically active compounds.