Decarbonylative Radical Coupling of α-Aminoacyl Tellurides: Single-Step Preparation of γ-Amino and α,β-Diamino Acids and Rapid Synthesis of Gabapentin and Manzacidin A

Simplified Modular Access to Enantiopure 1,2-Aminoalcohols via Ni-Electrocatalytic Decarboxylative Arylation

Chiral aminoalcohols are omnipresent in bioactive compounds. Conventional strategies to access this motif involve multiple-step reactions to install the requisite functionalities stereoselectively using conventional polar bond analysis. This study reveals that a simple chiral oxazolidine-based carboxylic acid can be readily transformed to substituted chiral aminoalcohols with high stereochemical control by Ni-electrocatalytic decarboxylative arylation. This general, robust, and scalable coupling can be used to synthesize a variety of medicinally important compounds, avoiding protecting and functional group manipulations, thereby dramatically simplifying their preparation.

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.

Core Structure-Oriented Asymmetric α-Allenylic Alkylation of Amino Acid Esters Enabled by Chiral Aldehyde/Palladium Catalysis

Aiming at the reported chiral synthons leading to manzacidins A and D, here we report a highly efficient catalytic asymmetric α-allenylic alkylation reaction of NH2-unprotected amino acid esters that is promoted by combined chiral aldehyde/palladium catalysis. Fifty examples of unnatural α,α-disubstituted amino acid esters are reported with good-to-excellent yields and stereoselectivities. Based on this methodology, a key intermediate leading to manzacidin C and its other three stereoisomers is prepared accordingly.

DeepSA: a deep-learning driven predictor of compound synthesis accessibility

With the continuous development of artificial intelligence technology, more and more computational models for generating new molecules are being developed. However, we are often confronted with the question of whether these compounds are easy or difficult to synthesize, which refers to synthetic accessibility of compounds. In this study, a deep learning based computational model called DeepSA, was proposed to predict the synthesis accessibility of compounds, which provides a useful tool to choose molecules. DeepSA is a chemical language model that was developed by training on a dataset of 3,593,053 molecules using various natural language processing (NLP) algorithms, offering advantages over state-of-the-art methods and having a much higher area under the receiver operating characteristic curve (AUROC), i.e., 89.6%, in discriminating those molecules that are difficult to synthesize. This helps users select less expensive molecules for synthesis, reducing the time and cost required for drug discovery and development. Interestingly, a comparison of DeepSA with a Graph Attention-based method shows that using SMILES alone can also efficiently visualize and extract compound's informative features. DeepSA is available online on the below web server ( https://bailab.siais.shanghaitech.edu.cn/services/deepsa/ ) of our group, and the code is available at https://github.com/Shihang-Wang-58/DeepSA .

Growing Utilization of Radical Chemistry in the Synthesis of Pharmaceuticals

Our current unhealthy lifestyle and the exponential surge in the population getting affected by a variety of diseases have made pharmaceuticals or drugs an imperative part of life, making the development of innovative strategies for drug discovery or the introduction of refined, cost-effective and modern technologies for the synthesis of clinically used drugs, a need of the hour. Ever since their discovery, free radicals and radical cations or anions as reactive intermediates have captivated the chemists, resulting in an exceptional utilization of these moieties throughout the field of chemical synthesis, owing to their unprecedented and widespread reactivity. Sticking with the idea of not judging the book by its cover, despite the conventional thought process of radicals being unstable and difficult to control entities, scientists and academicians around the globe have done an appreciable amount of work utilizing both persistent as well as transient radicals for a variety of organic transformations, exemplifying them with the synthesis of significant biologically active pharmaceutical ingredients. This review truly accounts for the organic radical transformations including radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling with metal-complexes and radical cations coupling with nucleophiles, that offers fascinating and unconventional approaches towards the construction of intricate structural frameworks of marketed APIs with high atom- and step-economy; complementing the otherwise employed traditional methods. This tutorial review presents a comprehensive package of diverse methods utilized for radical generation, featuring their reactivity to form critical bonds in pharmaceutical total synthesis or in building key starting materials or intermediates of their synthetic journey, acknowledging their excellence, downsides and underlying mechanisms, which are otherwise poorly highlighted in the literature. Despite great achievements over the past few decades in this area, many challenges and obstacles are yet to be unraveled to shorten the distance between the academics and the industry, which are all discussed in summary and outlook.

Visible-light-mediated synthesis of α,β-diamino esters via coupling of N,N-dimethylanilines and glyoxalic oxime ethers

A visible-light-mediated synthesis of α,β-diamino esters has been developed via the cross coupling of N,N-dimethylanilines with glyoxalic oxime ethers. This protocol involves the generation of α-aminoalkyl radicals under mild reaction conditions, provides α,β-diamino esters in good to excellent yields, and can be performed on a gram-scale.

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.

Convergent Assembly of Highly Oxygenated Natural Products Enabled by Intermolecular Radical Reactions

Natural products with a high ratio of sp³-hybridized atoms and oxygen-substituted stereogenic centers represent privileged structures for the development of pharmaceuticals and chemical probes. The multiple oxygen functionalities of these natural products endow their potent and selective biological activities, although they significantly heighten the challenge of their chemical assemblies. We focused on developing efficient strategies for the total syntheses of this biologically and chemically important class of molecules. A convergent strategy is more advantageous than a linear strategy for designing a shorter synthetic route because a convergent strategy enables direct coupling of functionalized fragments whereas a linear strategy involves stepwise construction of a molecule from its terminus. Radical reactions are preferred over polar reactions for the coupling of heavily functionalized and sp³-rich fragments, as they allow for C(sp³)-C(sp³) coupling without damaging diverse polar functional groups. With these considerations in mind, we designed radical-based convergent strategies for assembling highly oxygenated natural products. Here we summarize the concise total syntheses of asimicin (1, antibiotic activity), 1-hydroxytaxinine (2, cytotoxicity), polyoxins (3, antifungal activity), and hikizimycin (4, anthelmintic activity) as representative examples. Retrosynthetic disconnection at the central part of these molecules produces highly substituted α-alkoxy radicals as synthons. In the synthetic direction, the α-alkoxy radicals were generated from the corresponding α-alkoxyacyl tellurides in a unified fashion, and then utilized for four distinct coupling reactions. Formation of the Et radical from Et₃B and O₂ homolytically cleaves the C-Te bond of α-alkoxyacyl telluride, and the facile expulsion of carbon monoxide from the acyl radical leads to the α-alkoxy radical. Dimerization of the stabilized α-alkoxy radical resulted in the core structure of 1 with 10 contiguous stereocenters. The coupling adduct was derivatized to 1 through the attachment of two different carbon chains (17 steps as the longest linear sequence). Alternatively, intermolecular addition reactions of the α-alkoxy radicals to electron-deficient C═C, C═N, and C═O bonds, followed by Et₃B-mediated radical termination, led to the core structures of 2, 3, and 4, respectively. Intermolecular coupling between the α-alkoxy radical and the cyclohexenone derivative and intramolecular pinacol coupling gave rise to the 6/8/6-fused ring system of 2, which was transformed to 2 (26 steps). The two amino acid moieties of 3 were prepared by combining the α-alkoxy radical and the oxime and were then condensed to complete the synthesis of 3 (11 steps). Furthermore, a combination of α-alkoxyacyl telluride and Et₃B/O₂ realized a novel addition reaction of α-alkoxy radicals to aldehydes. This method was incorporated in the construction of the core 4-amino-5-deoxyundecose with 10 contiguous stereocenters, which was fabricated with two appendage structures to deliver 4. The four total syntheses described here demonstrate the versatility and robustness of intermolecular radical reactions. These syntheses will also provide new insights for retrosynthetic analyses in the field of organic chemistry and streamline synthetic routes to various bioactive natural products with multiple oxygen functionalities.

Radical-Based Synthesis and Modification of Amino Acids

Amino acids (AAs) are key structural motifs with widespread applications in organic synthesis, biochemistry, and material sciences. Recently, with the development of milder and more versatile radical-based procedures, the use of strategies relying on radical chemistry for the synthesis and modification of AAs has gained increased attention, as they allow rapid access to libraries of novel unnatural AAs containing a wide range of structural motifs. In this Minireview, we provide a broad overview of the advancements made in this field during the last decade, focusing on methods for the de novo synthesis of α-, β-, and γ-AAs, as well as for the selective derivatisation of canonical and non-canonical α-AAs.

Harnessing the biocatalytic potential of iron- and α-ketoglutarate-dependent dioxygenases in natural product total synthesis

Covering: up to the end of 2019Iron- and α-ketoglutarate-dependent dioxygenases (Fe/αKGs) represent a versatile and intriguing enzyme family by virtue of their ability to directly functionalize unactivated C-H bonds at the cost of αKG and O2. Fe/αKGs play an important role in the biosynthesis of natural products, valuable biologically active secondary metabolites frequently pursued as drug leads. The field of natural product total synthesis seeks to contruct these molecules as effeciently as possible, although natural products continue to challenge chemists due to their intricate structural complexity. Chemoenzymatic approaches seek to remedy the shortcomings of traditional synthetic methodology by combining Nature's biosynthetic machinery with traditional chemical methods to efficiently construct natural products. Although other oxygenase families have been widely employed for this purpose, Fe/αKGs remain underutilized. The following review will cover recent chemoenzymatic total syntheses involving Fe/αKG enzymes. Additionally, related information involving natural product biosynthesis, methods development, and non-chemoenzymatic total syntheses will be discussed to inform retrosynthetic logic and synthetic design.

Forging C(sp3)-C(sp3) Bonds with Carbon-Centered Radicals in the Synthesis of Complex Molecules

Radical fragment coupling reactions that unite intricate subunits have become an important class of transformations within the arena of complex molecule synthesis. This Perspective highlights some of the early contributions in this area, as well as more modern applications of radical fragment couplings in the preparation of natural products. Additionally, emphasis is placed on contemporary advances that allow for radical generation under mild conditions as a driving force for the implementation of radical fragment couplings in total synthesis.

Transition metal-free, visible-light-mediated construction of α,β-diamino esters via decarboxylative radical addition at room temperature

A metal-free photoredox catalyzed decarboxylative radical coupling of free-carboxylic acids and glyoxylic oximes was developed to synthesize α,β-diamino acids.

Convergent Synthesis of Taxol Skeleton via Decarbonylative Radical Coupling Reaction

The highly oxygenated 6/8/6-membered ABC-ring 2 of taxol was assembled in a convergent fashion. A decarbonylative radical reaction between α-alkoxyacyl telluride 4 and cyanocyclohexenone 5 linked the A- and C-rings and stereoselectively installed the C2- and C3-tertiary carbon centers of 3. After the C8-quaternary stereocenter was constructed, the C9-methyl ketone and the C11-vinyl triflate of 30 participated in Pd(0)-promoted cyclization of the eight-membered B-ring, giving rise to the taxol skeleton 2.

Synthesis of the Tetracyclic Structure of Batrachotoxin Enabled by Bridgehead Radical Coupling and Pd/Ni-Promoted Ullmann Reaction

The steroidal ABCD-ring system of the potent neurotoxin batrachotoxin was efficiently assembled in a convergent fashion. Bridgehead radical coupling between the simple AB-ring and D-ring fragments (3 and 4) formed the sterically congested linkage at the C9-oxygen-attached tetrasubstituted carbon. The C-ring was then cyclized by the Pd/Ni-promoted Ullmann reaction of the vinyl triflate and vinyl bromide of 19, giving rise to tetracyclic structure 1.

Unified Total Synthesis of Polyoxins J, L, and Fluorinated Analogues on the Basis of Decarbonylative Radical Coupling Reactions

Polyoxins J (1 a) and L (1 b) are important nucleoside antibiotics. The complex and densely functionalized dipeptide structures of 1 a and 1 b contain thymine and uracil nucleobases, respectively. Herein we report the unified total synthesis of 1 a, 1 b, and their artificial analogues 1 c and 1 d with trifluorothymine and fluorouracil structures. Decarbonylative radical coupling between α-alkoxyacyl tellurides and a chiral glyoxylic oxime ether led to chemo- and stereoselective construction of the ribonucleoside α-amino acid structures of 1 a-d without damaging the preinstalled nucleobases. The high applicability of the radical-based methodology was further demonstrated by preparation of the trihydroxynorvaline moiety of 1 a-d. The two amino acid fragments were connected and elaborated into 1 a-d (longest linear sequence: 11 steps). Compounds 1 a and 1 b assembled in this way exhibited potent activity against true fungi, while only 1 d was active against Gram-positive bacteria.

An enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones and 2-phthalimidoacrylates

A highly enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones to 2-phthalimidoacrylates has been developed using a bifunctional tertiary-amine thiourea catalyst.

Synthetic methods for 1,3-diamines

In this review, the synthetic methods for the preparation of 1,3-diamines and their applications in synthetic organic chemistry are summarized.

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.

Et3B-mediated two- and three-component coupling reactions via radical decarbonylation of α-alkoxyacyl tellurides: single-step construction of densely oxygenated carboskeletons

We devised new radical-based two- and three-component coupling reactions of sugar derivatives, and realized one-step construction of contiguously substituted polyol structures.

The single-step construction of various densely oxygenated carboskeletons was achieved by radical-based two- and three-component coupling reactions of sugar derivatives, without the need for light or heat. Et₃B/O₂-mediated decarbonylation readily converted α-alkoxyacyl tellurides to α-alkoxy carbon radicals, which intermolecularly added to glyoxylic oxime ether or enones to provide the two-component adducts. Furthermore, the three-component adducts were produced by an intermolecular aldol reaction between the aldehyde and the boron enolates generated by capture of the two-component radical intermediates by Et₃B. This powerful coupling method serves as a novel strategy for the convergent synthesis of polyol natural products.

Electrosynthesis of enaminones directly from methyl ketones and amines with nitromethane as a carbon source

An efficient and mechanistically different method for the electrosynthesis of enaminone directly from methyl ketones, amines and nitromethane was developed.