Concise total synthesis of (+)-lyconadin A

Stereoselective Vinylogous Aza-Pummerer Reaction of β,β-Disubstituted Enesulfinamides

Treatment of multisubstituted NH-enesulfinamides with tosyl isocyanate (TsNCO) at room temperature results in the formation of α-tosylcarbamoyloxy N-sulfenyl ketimines with high enantioselectivity. This process is believed to proceed via a vinylogous aza-Pummerer-type reaction pathway in which the sulfinyl oxygen atom in the enesulfinamides undergoes nucleophilic attack on tosyl isocyanate, triggering the subsequent transformations that enable the transfer of chirality from sulfur to carbon.

Huperzine alkaloids: forty years of total syntheses

Covering: up to 2023Huperzine alkaloids are a group of natural products belonging to the Lycopodium alkaloids family. The representative member huperzine A has a unique structure and exhibits potent inhibitory activity against acetylcholine esterase (AChE). This subfamily of alkaloids provides a great opportunity for developing synthetic methodologies and asymmetric synthesis. The efforts towards the synthesis of huperzine A have cultivated dozens of total syntheses and a rich body of new chemistry. Impressive progress has also been made in the synthesis of other huperzine alkaloids. The total syntheses of huperzines B, U, O, Q and R, structure reassignment and total syntheses of huperzines K, M and N have been reported in the past decade. This review focuses on the synthetic organic chemistry and the biosynthesis and medicinal chemistry of huperzines are also covered briefly.

Synthetic Study Aiming at the Tricyclic Core of 12-epi-JBIR-23/24

The synthetic study toward highly enantio- and diastereoselective synthesis of the tricyclic framework of 12-epi-JBIR-23/24, a natural product analogue showing inhibitory activity against four malignant pleural mesothelioma cell lines, is presented herein. In this synthesis, a rhodium-catalyzed asymmetric three-component Michael/aldol reaction introduces three consecutive tertiary carbon centers, while the unique epoxyquinol core motif is successfully forged via [3,3]-sigmatropic rearrangement of an allylic xanthate, vinylogous Pummerer rearrangement, and a selective mesylation/epoxidation cascade of a triol.

An invocation for computational evaluation of isomerization transforms: cationic skeletal reorganizations as a case study

Covering: 2010 to 2020This review article describes how cationic rearrangement reactions have been used in natural product total synthesis over the last decade as a case study for the many productive ways by which isomerization reactions are enabling for synthesis. This review argues that isomerization reactions in particular are well suited for computational evaluation, as relatively simple calculations can provide significant insight.

Organocatalytic Enantioselective 1,3-Dipolar [6+4] Cycloadditions of Tropone

A highly stereoselective 1,3-dipolar [6+4] cycloaddition towards bridged azabicyclo[4.3.1]decane scaffolds has been developed, reacting aldehydes, 2-aminomalonates and tropone under mild conditions in the presence of a chiral phosphoric acid catalyst. The scope is demonstrated for a series of aldehydes and 2-aminomalonates, and the reaction proceeds in high yields, >95:5 d.r. and up to 99 % ee. A series of transformations, as well as a mechanistic proposal, are presented.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Metal-Free Electrophilic Alkynylation of Sulfenate Anions with Ethynylbenziodoxolone Reagents

Alkynyl sulfoxides are important building blocks with a unique reactivity in organic chemistry, but only a few reliable methods have been reported to synthesize them. A novel route to access alkynyl sulfoxides is reported herein by using ethynyl benziodoxolone (EBX) reagents to trap sulfenate anions generated in situ, via a retro-Michael reaction. The reaction takes place under metal-free and mild conditions. It is compatible with aryl, heteroaryl, and alkyl sulfoxides with up to 90% yield. This practical access to alkynyl sulfoxides is expected to facilitate the application of these useful building blocks in organic synthesis.

An Approach to the 9-Oxo-10-oxabicyclo[5.3.0]dec-2-ene Core of the Guaianolide and Pseudoguaianolide Sesquiterpenes via a Domino Electrocyclic Ring-Opening/Carboxylic Acid Trapping of a gem-Dibromocyclopropane

A domino silver(I)-promoted electrocyclic 2π-disrotatory electrocyclic ring-opening/intramolecular nucleophilic trapping of [ n.1.0]-dibromocyclopropanes by tethered carboxylic acids results in cyclization to butyrolactones fused to six- and seven-membered carbocycles. In the case of bicyclic [4.3.0] lactones the cis-fused stereoisomer was formed, whereas for the bicyclic [5.3.0] lactones the trans-fused stereoisomer was formed. Optimal conditions for the reaction used silver(I) trifluoroacetate (2.0 equiv) in trifluoroethanol or with added pyridine (2.0 equiv) and NaPF₆ (5.0 equiv). The dibromocyclopropane precursors were made through cyclopropanation with in situ-generated dibromocarbene. The trans-fused lactones are potentially useful building blocks for pseudoguaianolide, guaianolide, and xanthanolide total synthesis. A computational study on the conformational preferences of these systems indicates that the trans-fused bicyclic [5.3.0] butyrolactones are lower in energy than the corresponding cis-fused lactones at the B3LYP/cc-pVTZ level of theory.

Second-Generation Synthesis of (+)-Fastigiatine Inspired by Conformational Studies

(+)-Fastigiatine is a complex alkaloid isolated from the alpine club moss Lycopodium fastigatum, most commonly found in New Zealand. It has been the subject of two successful synthetic campaigns. A second-generation route toward fastigiatine was developed to resolve two problematic steps from our initial synthesis. Selective reduction and protection of the C13 ketone improved the yield and reliability of the dibromocarbene ring expansion step. In the prior synthesis, cuprate addition to the C10 enone generated a 1:1 mixture of isomers in an advanced intermediate. Protection of the C13 alcohol with a large silyl group changed the conformational preference of the enone and led to a more selective conjugate addition to produce the desired β-epimer at C10. MacMillan's decarboxylative photoredox addition method proved to be more practical than the prior aminomethyl cuprate addition chemistry. The second-generation synthesis is longer than the original but improves the selectivity and reproducibility of the overall route.

Concise synthesis of (+)-fastigiatine

(+)-Fastigiatine was assembled in six steps from (R)-5-methylcyclohex-2-en-1-one. Intermolecular Diels-Alder reaction introduced most of the carbon atoms for the target. The two Boc-protected nitrogen atom building blocks were introduced by a Suzuki coupling and a cuprate addition. A biomimetic transannular Mannich reaction generated the two quaternary centers at a late stage. Each step builds core bonds, and combined with a minimalist protecting group strategy, this approach led to a very concise synthesis.

Exceedingly Concise and Elegant Synthesis of (+)-Paniculatine, (-)-Magellanine, and (+)-Magellaninone

Starting from inexpensive (+)-pulegone as the chiral building block, a highly convergent synthesis of the unusual diquinane-based structures of (+)-paniculatine (1), (-)-magellanine (2), and (+)-magellaninone (3), has been achieved. This approach is based upon a tandem acylation-alkylation of ketoester 8 and palladium-catalyzed olefin insertion, oxidation, and hydrogenation for construction of the tetracyclic framework. This exceedingly concise strategy, requiring only 12-14 steps, is the shortest to date.

The first asymmetric total synthesis of lycoposerramine-R

The first asymmetric total synthesis of lycoposerramine-R was accomplished by a strategy featuring the stereoselective intramolecular aldol cyclization giving a cis-fused 5/6 bicyclic skeleton and a new method for the construction of the pyridone ring via the aza-Wittig reaction, thereby establishing the absolute configuration of the natural product.

Neuritogenic surfaces using natural product analogs

Neuritogenic surfaces are generated by a simple dip-coating procedure, as glass slides are coated with a neurotrophin-like small organic molecule in the presence of a collagen matrix. The surfaces retain their biological activity for multiple cycles and the protocol is suitable for various substrates and coating conditions.

Total Syntheses of Lyconadins: Finding Efficiency and Diversity

Lyconadins A-C are important members of the Lycopodium alkaloid family with challenging structural features and interesting biological profile. Herein, various synthetic strategies and methods for their preparation are summarized with the focus on constructive bond formation and our efficient and divergent synthesis based on functional group pairing (FGP) strategy.

Divergent total syntheses of lyconadins A and C

Divergent and concise total syntheses of two lycopodium alkaloids, lyconadins A and C have been developed. The synthesis of lyconadin A, having potent neurotrophic activity, features an efficient one-pot ketal removal and formal aza-[4+2] cyclization to form the cagelike core structure. A tandem ketal removal/Mannich reaction was developed to build the tricyclic structure of lyconadin C. Both lyconadins A and C were synthesized from a pivotal intermediate.

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.