Synthesis of the Lycopodium Alkaloid (+)-Lycoflexine

Total syntheses of macleanine and lycoposerramine-S

Total syntheses of fawcettimine-class Lycopodium alkaloids having an imino bridge between C5 and C13 were accomplished. Fawcettimine was first prepared in 10 steps from a known compound, and the characteristic structures, including the imino bridge, were constructed via the formation of a bridgehead imine.

Total Synthesis of Lyconesidine B, a Lycopodium Alkaloid with an Oxygenated, Amine-Type Fawcettimine Core

This report describes the total synthesis of the complex, oxygenated tetracyclic alkaloid, lyconesidine B. The key synthetic challenge involves diastereoselective generation of a decahydroquinoline ring with a quaternary carbon at the angular position via domino cyclopropanation, ring-opening, and reduction. Another crucial step is the domino ene-yne metathesis involving a quaternary ammonium ion, leading to the construction of a decahydroazaazulen framework.

Synthetic Study toward the Total Synthesis of Lycoclavatumide

The synthetically challenging and highly functionalized azabicyclo[6.4.1] ring system, which is found in lycopodium alkaloid lycoclavatumide and some natural molecules, was synthesized for the first time. The key reaction was a diastereoselective type II [5+2] cycloaddition with excellent functional group compatibility. We tried to install the desired eight-membered ring in the final product by RCM reaction.

Recent Advances in One-Pot Enyne Metathesis Processes for the Preparation of Biologically and Medicinally Relevant Compounds

Enyne metathesis reactions are powerful tools for the preparation of a wide range of synthetic and natural chemical substances with increasing efficiency and environmental sustainability. The driving force of the reaction is the formation of a stable conjugated system, i.e., a diene, which through further functionalization steps can be used for the construction of skeletally complex molecular architectures. These concepts are exploited to design cascade reaction sequences, where multiple rings can be formed in a one-pot fashion by combining metathetic protocols with various chemical transformations. The strong correlation between synthetic organic chemistry and medicinal chemistry prompted us to review the most notable approaches for the synthesis of biologically relevant compounds via enyne metathesis-based one-pot processes. With the aim to provide a modern and practical overview, by taking into consideration the scientific literature on this topic, we have focused the majority of our attention on the research performed in the last decade. This review covers the literature from 2003 to 2020.

1 Introduction

2 Ethylene-Mediated Processes

3 RCEYM/CM and CEYM/RCM Processes

4 Enyne Metathesis/Diels–Alder-Based Processes

5 RCM of Dienynes

6 RCM of Tethered Dienynes

7 Relay Metathesis

8 Ring-Rearrangement Metathesis

9 RCEYM/Transition-Metal-Catalyzed C–C Bond-Forming Processes

10 Conclusions

11 List of Acronyms

Deciphering the Biosynthetic Mechanism of Pelletierine in Lycopodium Alkaloid Biosynthesis

Pelletierine, a proposed building block of Lycopodium alkaloids (LAs), was demonstrated to be synthesized via the non-enzymatic Mannich-like condensation of Δ¹-piperideine and 3-oxoglutaric acid produced by two new type III PKSs (HsPKS4 and PcPKS1) characterized from Huperzia serrata and Phlegmariurus cryptomerianus, respectively. The findings provide new insights for further understanding the biosynthesis of LAs such as huperzine A.

Lycosquarrines A-R, Lycopodium Alkaloids from Phlegmariurus squarrosus

Eighteen new Lycopodium alkaloids, lycosquarrines A-R (1-18), and eight known alkaloids were isolated from the aerial parts of Phlegmariurus squarrosus. Compounds 1-5 and 19, identified from natural sources for the first time, are uncommon lycopodine-type alkaloids with β-oriented H-4. Pentacyclic 4 and 5 represent the first examples of 5,12- and 5,11-epoxy Lycopodium alkaloids, respectively, and an epoxide-opening cyclization reaction is suggested to be a key step in their biosynthesis. Compound 18 possesses the same carbon skeleton as carinatine A (22), which was previously reported as a unique Lycopodium alkaloid with a 5/6/6/6 ring system. X-ray crystallographic data analysis was used to determine the absolute configuration of 18, leading to the establishment of the absolute configuration of 22 by comparison of the ECD spectra. An anti-acetylcholinesterase activity assay showed that 11 and 20 exhibited inhibitory activities with IC₅₀ values of 4.2 and 2.1 μM, respectively.

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

This account surveys the current progress on the application of intra- and intermolecular enyne metathesis as main key steps in the synthesis of challenging structural motifs and stereochemistries found in bioactive compounds. Special emphasis is placed on ruthenium catalysts as promoters of enyne metathesis to build the desired 1,3-dienic units. The advantageous association of this approach with name reactions like Grignard, Wittig, Diels–Alder, Suzuki–Miyaura, Heck cross-coupling, etc. is illustrated. Examples unveil the generality of such tandem reactions in providing not only the intricate structures of known, in vivo effective substances but also for designing chemically modified analogs as valid alternatives for further therapeutic agents.

Vinyl Triflate-Aldehyde Reductive Coupling-Redox Isomerization Mediated by Formate: Rhodium-Catalyzed Ketone Synthesis in the Absence of Stoichiometric Metals

Direct conversion of aldehydes to ketones is achieved via rhodium-catalyzed vinyl triflate-aldehyde reductive coupling-redox isomerization mediated by potassium formate. This method circumvents premetalated C-nucleophiles and discrete redox manipulations typically required to form ketones from aldehydes.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Transition metal catalyzed stereodivergent synthesis of syn- and anti-δ-vinyl-lactams: formal total synthesis of (-)-cermizine C and (-)-senepodine G

A stereodivergent and diastereoselective transition-metal-catalyzed intramolecular hydroamidation of allenes and alkynes furnishing δ-vinyl-lactams is reported. Employing a rhodium catalyst allowed for the selective synthesis of the syn-δ-lactam. Conversely, a palladium catalyst led to the formation of the anti-δ-lactam in high selectivity. The new method shows high functional group compatibility and assorted synthetic transformations were demonstrated as well as its utility for the enantioselective formal total syntheses of (-)-cermizine C and (-)-senepodine G.

Formal Total Synthesis of (±)-Lycojaponicumin C

The formal total synthesis of (±)-lycojaponicumin C has been accomplished. Key transformations include a Rh-catalyzed formal [3 + 2] cycloaddition reaction to construct the bicyclic [3.3.0] scaffold bearing two vicinal quaternary carbon centers, a stereoselective γ-hydroxyl directed Michael addition to introduce the vinyl group at a bulky position, and a late-stage ring-closing metathesis reaction to form the cyclohexanone ring.

Metal-catalyzed enyne cycloisomerization in natural product total synthesis

Enyne cycloisomerization has become a powerful and attractive strategy for the construction of cyclic compounds, thus possessing great potential for applications in total synthesis of natural products and pharmaceuticals.

Ruthenium-Catalyzed Metathesis Cascade Reactions in Natural Products Synthesis

In this account, we provide a brief summary of recent developments in ruthenium-catalyzed metathesis cascade reactions towards the total synthesis of natural products. We also highlight recent progress from our own laboratory regarding the synthesis of securinega alkaloids and humulanolides, which has resulted in the development of novel ruthenium-catalyzed metathesis cascade reactions. Inspired and guided by the pioneering and elegant research conducted in this area, we developed a regio-controlled relay dienyne metathesis cascade reaction and a cyclobutene-promoted RCM/ROM/RCM cascade reaction for the synthesis of securinega alkaloids and humulanolides, respectively.

Cross-Metathesis of Brønsted Acid Masked Alkenylamines with Acrylates for the Synthesis of Polyamide Monomers

Ruthenium-alkylidene-catalyzed cross-metathesis of a range of homologous alkenylamine salts provides expedient and high-yielding routes to commercially valuable polyamide monomers using a single catalyst, telescopic workup, and mild experimental conditions.

Expedient Synthesis of (+)-Lycopalhine A

Two amino acids play a key role in the first total synthesis of lycopalhine A. L-glutamic acid serves as a convenient chiral starting material for the 13-step synthesis, and l-proline promotes an unusual 5-endo-trig Mannich cyclization that generates the central pyrrolidine ring of the Lycopodium alkaloid. The bicyclo[3.3.0]octanol moiety of the molecule is formed through an intramolecular aldol addition that may occur spontaneously in nature.

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.

Diversity-oriented synthesis of Lycopodium alkaloids inspired by the hidden functional group pairing pattern

Natural products continue to provide a rich source of inspiration for both chemists and biologists. The efficient synthesis of bioactive natural products or natural product-like molecules has offered tremendous opportunities for complex biological processes exploration and drug discovery. However, because natural products usually contain numerous stereogenic centres and polycyclic ring systems, significant synthetic challenges remain. Here we employ the build/couple/pair strategy that is frequently used in diversity-oriented synthesis to obtain skeletally diverse compounds with complexities comparable to natural products. Inspired by the functional group pairing patterns hidden in Lycopodium alkaloids, we efficiently and in parallel construct four natural products, (+)-Serratezomine A, (-)-Serratinine, (+)-8α-Hydroxyfawcettimine and (-)-Lycoposerramine-U, as well as six different unnatural scaffolds, following the advanced build/couple/pair algorithm. This newly developed strategy is expected to be applied to the efficient synthesis of other complex natural products possessing functional group pairing patterns as well as skeletally diverse natural product-like molecules.

A gram-scale route to phlegmarine alkaloids: rapid total synthesis of (−)-cermizine B

The asymmetric total synthesis of the cis-phlegmarine alkaloid cermizine B was achieved rapidly and on a gram-scale by an uninterrupted eight-step sequence and a final reduction step.

Azabicycles construction: the transannular ring contraction with N-protected nucleophiles

Synthetic strategies are one of the most critical factors for the success of a synthetic campaign, but most importantly they are crucial for the economy and the efficiency of the sequence.

Divergent total syntheses of (-)-lycopladine D, (+)-fawcettidine, and (+)-lycoposerramine Q

Enantioselective total syntheses of (+)-fawcettidine and (+)-lycoposerramine Q as well as the first total synthesis of (-)-lycopladine D from a common intermediate have been accomplished by a divergent path. The common intermediate was derived from a Hajos-Parrish-like diketone by a stereoselective Birch reduction and a Suzuki coupling. The synthesis of (-)-lycopladine D featured an allylic oxidation and a biomimetic aminoketalization while the route to (+)-fawcettidine and (+)-lycoposerramine Q highlighted an oxidative rearrangement.

Pyridone annulation via tandem Curtius rearrangement/6π-electrocyclization: total synthesis of (-)-lyconadin C

A concise, enantioselective total synthesis of the Lycopodium alkaloid (-)-lyconadin C was achieved in 12 steps and high overall yield. Key features include construction of a luciduline congener through Mannich-type cyclization and a one-pot, tandem Curtius rearrangement/6π-electrocyclization to fashion the 2-pyridone system of lyconadin C.

Total synthesis of the Lycopodium alkaloid serratezomine A using free radical-mediated vinyl amination to prepare a β-stannyl enamine linchpin

Serratezomine A is a member of the structurally diverse class of compounds known as the Lycopodium alkaloids. The key supporting studies and successful total synthesis of serratezomine A are described in this account. Significant features of the synthesis include the first application of free radical mediated vinyl amination and Hwu's oxidative allylation in a total synthesis and an intramolecular lactonization via a transannular S(N)i reaction. Minimal use of protecting groups and the highly diastereoselective formation of a hindered, quaternary stereocenter using an umpolung allylation are also highlights from a strategy perspective. Observation of quaternary carbon epimerization via a retro-Mannich/Mannich sequence highlights the additional challenge presented by the axial alcohol at C8 in serratezomine A.