Organocatalyst-mediated five-pot synthesis of (-)-quinine

Total Syntheses of (+)-Aigialospirol and (+)-7',8'-Dihydroaigialospirol by a One-Pot Stepwise Approach

(+)-Aigialospirol and (+)-7',8'-dihydroaigialospirol are known to be spiroketal polyketide-type natural products isolated from mangrove-derived fungus Aigialus parvus BCC 5311. These polyketides are structurally characterized by fusing resorcylic acid lactone and spiroketal moieties containing six asymmetric carbon centers. In this paper, we describe concise and stereoselective syntheses of these natural products based on biosynthesis-inspired transformation in nine steps. The total syntheses are highlighted by a one-pot stepwise synthesis involving (i) stereoselective lactone ring formation from a chiral epoxide, (ii) reduction of alkyne, (iii) global deprotection, and (iv) spiroketal formation, which are performed in the final step of the total synthesis.

Recent advances in the total synthesis of alkaloids using chiral secondary amine organocatalysts

Since the early 21st century, organocatalytic reactions have undergone significant advancements. Notably, numerous asymmetric reactions utilizing chiral secondary amine catalysts have been developed and applied in the total synthesis of natural products. In this review, we provide an overview of alkaloid syntheses reported since 2017, categorized by scaffold, with a focus on key steps involving asymmetric reactions catalyzed by secondary amine organocatalysts.

The Quinine Odyssey: A Barometer of the State of Organic Synthesis Over Centuries

The year 2024 marks the 80th anniversary of the landmark formal synthesis of (±)-quinine completed by Woodward and Doering. This article examines the evolution of approaches to access this storied Cinchona alkaloid natural product which represent a microcosm the progress that has been made in organic synthesis over the past ~170 years. Seminal contributions led by Pasteur, Rabe, Woodward, Uskoković, Stork, Jacobsen, Hayashi, Maulide and others are discussed.

An Artificial Enzyme for Asymmetric Nitrocyclopropanation of α,β-Unsaturated Aldehydes-Design and Evolution

The introduction of an abiological catalytic group into the binding pocket of a protein host allows for the expansion of enzyme chemistries. Here, we report the generation of an artificial enzyme by genetic encoding of a non-canonical amino acid that contains a secondary amine side chain. The non-canonical amino acid and the binding pocket function synergistically to catalyze the asymmetric nitrocyclopropanation of α,β-unsaturated aldehydes by the iminium activation mechanism. The designer enzyme was evolved to an optimal variant that catalyzes the reaction at high conversions with high diastereo- and enantioselectivity. This work demonstrates the application of genetic code expansion in enzyme design and expands the scope of enzyme-catalyzed abiological reactions.

Organocatalyst-mediated asymmetric one-pot/two domino/three-component coupling reactions for the synthesis of trans-hydrindanes

Highly substituted trans-hydrindanes were synthesized by the three-component coupling reactions of 1,3-diethyl 2-(2-oxopropylidene)propanedioate and two different α,β-unsaturated aldehydes catalyzed by diphenylprolinol silyl ether. The reaction proceeds via two successive independent catalytic domino reactions in a one-pot reaction by a single chiral catalyst. Domino reactions involve Michael/Michael and Michael/aldol reactions to afford trans-hydrindanes with excellent diastereoselectivity and nearly optically pure form.

Asymmetric Construction of the Core of C6, C7-Epoxy Daphnane Diterpenoid Orthoesters

Asymmetric construction of the core of C6, C7-epoxy daphnane diterpenoid orthoesters is developed through a convergent synthetic strategy. The salient features include a diastereoselective nucleophilic assembly of two bulky cyclic fragments, an oxidative cleavage/transesterification/aldol cascade to fashion the seven-membered ring, and a base-mediated transesterification/retro-aldol/aldol/epoxidation cascade to install the epoxy moiety with proper stereochemistry.

Recent advances in synthesizing and utilizing nitrogen-containing heterocycles

The use of organocatalysts and a pot economy has strengthened recent organic syntheses. Synthetic methodologies may be applicable in laboratory preparation or in the industrial production of valuable organic compounds. In most cases, synthetic challenges are overcome by highly efficient and environmentally benign organocatalysts in a pot-economical manner. This is exemplified by the recent synthesis of tetrahydropyridine-containing (-)-quinine.

Organocatalyst-mediated, pot-economical total synthesis of latanoprost

The enantioselective total synthesis of latanoprost, an antiglaucoma agent, has been accomplished with excellent diastereo- and enantioselectivities in a pot-economical manner using six reaction vessels. An enantioselective Krische allylation was conducted in the first pot. In the second pot, olefin metathesis, silyl protection, and hydrogenolysis proceeded efficiently. In the third pot, an organocatalyst-mediated Michael reaction proceeded with excellent diastereoselectivity. The fourth pot involved a substrate-controlled Mukaiyama intramolecular aldol reaction and elimination of HNO2 to afford a methylenecyclopentanone, also with excellent diastereoselectivity. The fifth pot involved a Michael reaction of vinyl cuprate. In the sixth pot, three reactions, a cis-selective olefin metathesis, diastereoselective reduction, and deprotection, afforded latanoprost. Nearly optically pure latanoprost was obtained, and the total yield was 24%.

Cinchona alkaloids - acid, anion-driven fluorescent INHIBIT logic gates with a receptor1-fluorophore-spacer-receptor2 format and PET and ICT mechanisms

The fluorescent natural products, quinine, quinidine, cinchonine and cinchonidine are demonstrated as H⁺-enabled, halide-disabled (Cl^-, Br^- or I^-) INHIBIT and INHIBIT-OR combinatorial logic gates in water. More fluorescent natural products with intrinsic logic properties await to be discovered.

Variable structure diversification by multicatalysis: the case of alcohols

Given that alcohol moieties are present in a great diversity of valuable fine chemicals from nature and synthesis, methods enabling their structure diversification are highly sought after. Catalysis proved to enable the development of new transformations that are beyond the inherent reactivity of alcohols. However, modifying the structure of alcohols at certain unbiased positions remains a major challenge or requires tedious multistep procedures. Recently, increased attention has been given to multicatalyis, which combines multiple reactions and catalysts within one system, creating room for discovering previously inaccessible reactivities or increasing the overall efficiency of multistep transformations. This feature article focuses on demonstrating various aspects of devising such multicatalytic systems that modify the structure of alcohol-containing compounds. Special attention is given to highlighting the challenges and advantages of multicatalysis, and in a broader context discussing how the field of catalysis may progress toward more complex systems.