Total synthesis of natural tert-alkylamino hydroxy carboxylic acids

Recent asymmetric synthesis of natural products bearing an α-tertiary amine moiety via temporary chirality induction strategies

Covering: 2013 to 2023The α-tertiary amine moiety is a common structural motif in natural alkaloids and is frequently associated with intriguing biological activities and inherent synthetic challenges. A major hurdle in the total synthesis of these alkaloids is the asymmetric construction of the α-tertiary amine moiety. Temporary chirality inductions have been effective strategies employed to address this issue, particularly in natural product synthesis. The temporary chirality induction strategies in α-tertiary amine synthesis can be broadly classified into three categories based on the types of temporary chirality involved: Seebach's self-regeneration of stereocenters (SRS), C-to-N-to-C chirality transfer, and memory of chirality (MOC). This review highlights the recent advancements in temporary chirality induction strategies for the total synthesis of α-tertiary amine-containing natural products between 2013 and 2023.

Asymmetric Cyanation of α-Ketimino Ester Derivatives with Chiral Ru-Li Combined Catalysts

Asymmetric cyanation of α-ketimino esters catalyzed by combined systems of amino acid/BINAP derivative/Ru(II) complexes and lithium compounds was examined. The use of an appropriate combination of amino acid and BINAP ligands achieved high enantioselectivity for a variety of α-alkynyl (Val/XylBINAP/Ru), α-alkenyl (Val/TolBINAP/Ru), and α-aryl imino esters (Val/XylBINAP/Ru) as well as an isatin-derived cyclic imino amide (t-Leu/BINAP/Ru) to afford the α-cyano-α-amino esters and the amide with an α-nitrogen-substituted quaternary chiral center with up to 98% ee.

Recent advances in the total synthesis of polyhydroxylated alkaloids via chiral oxazines

This review summarizes recently established methodologies developed for the enantioselective and diastereoselective synthesis of chiral 1,3-oxazines. These compounds are of interest as advanced synthetic intermediates in the total synthesis of structurally complex and biologically active polyhydroxylated alkaloids such as (+)-1-deoxynojirimycin, (-)-anisomycin, (+)-castanospermine, (+)-casuarine, (-)-conduramine F-1, (-)-sphingofungin B, Neu5Ac methyl ester, and other natural products. The devised synthetic approach aims to offer a direct, efficient, and adaptable method for obtaining both pure enantiomers and pure diastereomers. It revolves around utilizing chiral building blocks like syn,syn-, syn,syn,anti-, syn,anti-, syn,anti,syn-, anti,syn-, anti,syn,syn-, and anti,syn,anti-oxazines. By integrating oxazine chemistry with established and innovative transformations, this approach enabled the synthesis of 30 polyhydroxylated amines across various studies conducted between 2007 and 2022.

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Bond Energy Enabled Amines Distinguishing: Chemo-, Regioselective 1,3-Diamination of (Trifluoromethyl)alkenes with Different Amines by Two C(sp3)-F Bonds Cleavage

The methods to distinguish different amines are rarely investigated. In this manuscript, a bond energy enabled amines distinguishing strategy is reported. With (trifluoromethyl)alkenes as linchpins, a chemo-, regioselective three-component defluorinative...

α-Functionally Substituted α,β-Unsaturated Aldehydes as Fine Chemicals Reagents: Synthesis and Application

α-Functionalized α,β-unsaturated aldehydes is an important class of compounds, which are widely used in fine organic synthesis, biology, medicine and pharmacology, chemical industry, and agriculture. Some of the 2-substituted 2-alkenals are found to be the key metabolites in plant and animal cells. Therefore, the development of efficient methods for their synthesis attracts the attention of organic chemists. This review focusses on the recent advances in the synthesis of 2-functionally substituted 2-alkenals. The approaches to the preparation of α-alkyl α,β-unsaturated aldehydes are not included in this review.

Synthesis of proteasome inhibitor 6-deoxy-omuralide and its enantiomer using stereoselective alkylation of substituted proline ester

A potent 20S proteasome inhibitor, 6-deoxy-omuralide was stereoselectively synthesized in 20 steps with 5.1% overall yield staring from a chiral boron agent and d-glyceraldehyde acetonide. The stereoselective alkylation of the substituted proline ester with 3-iodo-2-methylprop-1-ene served as the key step. The enantiomer of 6-deoxy-omuralide was achieved in 20 steps with 4.6% overall yield by just changing the chiral boron reagents in the first step. Our current work provides a flexible approach to 6-deoxy-omuralide and its enantiomer with the adornment at the C4 position.

A step-economic and one-pot access to chiral Cα-tetrasubstituted α-amino acid derivatives via a bicyclic imidazole-catalyzed direct enantioselective C-acylation

C^α-Tetrasubstituted α-amino acids are ubiquitous and unique structural units in bioactive natural products and pharmaceutical compounds. The asymmetric synthesis of these molecules has attracted a lot of attention, but a more efficient method is still greatly desired. Here we describe the first sequential four-step acylation reaction for the efficient synthesis of chiral C^α-tetrasubstituted α-amino acid derivatives from simple N-acylated amino acids via an auto-tandem catalysis using a single nucleophilic catalyst. The synthetic efficiency is improved via a direct enantioselective C-acylation; the methodology affords the corresponding C^α-tetrasubstituted α-amino acid derivatives with excellent enantioselectivities (up to 99% ee). This step-economic, one-pot, and auto-tandem strategy provides facile access to important chiral building blocks, such as peptides, serines, and oxazolines, which are often used in medicinal and synthetic chemistry.

The first four-step sequential reaction for the synthesis of C^α-tetrasubstituted chiral α-amino acid derivatives via auto-tandem catalysis has been developed.

Copper-Catalyzed Enantioselective Synthesis of Oxazolines from Aminotriols via Asymmetric Desymmetrization

A copper-catalyzed enantioselective transformation of tris(hydroxymethyl)aminomethane-derived aminotriols was developed to provide multisubstituted oxazolines with a tetrasubstituted carbon center. The present transformation consisted of sequential reactions involving mono-sulfonylation of aminotriols, subsequent intramolecular cyclization to afford prochiral oxazoline diols, and sulfonylative asymmetric desymmetrization of resultant oxazoline diols. In addition, the kinetic resolution process would be involved in the sulfonylative asymmetric desymmetrization step, which would amplify the enantiopurities of the desired products. Various aminotriols were tolerated in the present reaction, affording the desired oxazolines in good to high yields with excellent enantioselectivities. The synthetic utility of the present reaction was demonstrated by the transformation of the optically active oxazoline into a chiral α-tertiary amine motif.

Formal Total Synthesis of Manzacidin B via Sequential Diastereodivergent Henry Reaction

A formal total synthesis of manzacidin B is described. β,β-Disubstituted γ-hydroxy-β-aminoalcohol, the key structure of manzacidin B, is stereoselectively constructed via sequential Henry reactions. By taking advantage of noncovalent interactions, such as intramolecular hydrogen bonding and chelation, we could diastereodivergently control the stereoselectivity of the Henry reaction.

Application of Threonine Aldolases for the Asymmetric Synthesis of α-Quaternary α-Amino Acids

We report the synthesis of diverse β-hydroxy-α,α-dialkyl-α-amino acids with perfect stereoselectivity for the α-quaternary center through the action of l- and d-specific threonine aldolases. A wide variety of aliphatic and aromatic aldehydes were accepted by the enzymes and conversions up to >80 % were obtained. In the case of d-selective threonine aldolase from Pseudomonas sp., generally higher diastereoselectivities were observed. The applicability of the protocol was demonstrated by performing enzymatic reactions on preparative scale. Using the d-threonine aldolase from Pseudomonas sp., (2R,3S)-2-amino-3-(2-fluorophenyl)-3-hydroxy-2-methylpropanoic acid was generated in preparative amounts in one step with a diastereomeric ratio >100 favoring the syn-product. A Birch-type reduction enabled the reductive removal of the β-hydroxy group from (2S)-2-amino-3-hydroxy-2-methyl-3-phenylpropanoic acid to generate enantiopure l-α-methyl-phenylalanine via a two-step chemo-enzymatic transformation.

A Useful Allene for the Stereoselective Synthesis of Protected Quaternary 2-Amino-2-vinyl-1,3-diols

Treatment of readily available allene 1 with Cy₂BH followed by addition of an aldehyde led to quaternary protected 2-amino-2-vinyl-1,3-diols in high yield and excellent stereochemical purity. The choice of benzoyl as N-protecting group is critical since the observed N- to O-Bz transfer during the process prevents later undesired isomerizations in the adducts and keeps all heteroatoms protected.

Synthetic approaches towards alkaloids bearing α-tertiary amines

Alkaloids account for some of the most beautiful and biologically active natural products. Although they are usually classified along biosynthetic criteria, they can also be categorized according to certain structural motifs. Amongst these, the α-tertiary amine (ATA), i.e. a tetrasubstituted carbon atom surrounded by three carbons and one nitrogen, is particularly interesting. A limited number of methods have been described to access this functional group and fewer still are commonly used in synthesis. Herein, we review some approaches to asymmetrically access ATAs and provide an overview of alkaloid total syntheses where those have been employed.

Natural Product Primary Sulfonamides and Primary Sulfamates

Primary sulfonamide and primary sulfamate functional groups feature prominently in the structures of U.S. FDA-approved drugs. However, the natural product chemical space contains few examples of these well-known zinc-binding chemotypes, with just two primary sulfonamide and five primary sulfamate natural products isolated and characterized to date. One of these natural products was isolated from a marine sponge, with the remainder isolated from Streptomyces species. In this review are outlined for the first time the discovery, isolation, striking breadth of bioactivity, and total synthesis (where available) for this rare group of natural products.

2-Vinyl Threoninol Derivatives via Acid-Catalyzed Allylic Substitution of Bisimidates

A diastereoselective synthesis of 4-vinyl oxazolines syn-2 was developed based on an acid-catalyzed cyclization of bistrichloroacetimidates (E)-1. The reaction likely involves an allyl carbenium ion intermediate in which the adjacent stereocenter directs the stereoselectivity for C-N bond formation. Oxazolines syn-2 were transformed to C-quaternary threoninol, threoninal, and threonine derivatives which can be further incorporated into complex natural compounds.

Chirality extension of an oxazine building block en route to total syntheses of (+)-hyacinthacine A2 and sphingofungin B

Concise total syntheses of (+)-hyacinthacine A₂ and sphingofungin B were achieved by palladium(0)-catalyzed intramolecular oxazine formation and diastereoselective nucleophilic additions.

Neurotrophic natural products: chemistry and biology

Neurodegenerative diseases and spinal cord injury affect approximately 50 million people worldwide, bringing the total healthcare cost to over 600 billion dollars per year. Nervous system growth factors, that is, neurotrophins, are a potential solution to these disorders, since they could promote nerve regeneration. An average of 500 publications per year attests to the significance of neurotrophins in biomedical sciences and underlines their potential for therapeutic applications. Nonetheless, the poor pharmacokinetic profile of neurotrophins severely restricts their clinical use. On the other hand, small molecules that modulate neurotrophic activity offer a promising therapeutic approach against neurological disorders. Nature has provided an impressive array of natural products that have potent neurotrophic activities. This Review highlights the current synthetic strategies toward these compounds and summarizes their ability to induce neuronal growth and rehabilitation. It is anticipated that neurotrophic natural products could be used not only as starting points in drug design but also as tools to study the next frontier in biomedical sciences: the brain activity map project.