An Eight‐Step Total Synthesis of Pyrroloquinolone‐Type Lycopodium Alkaloid via a Tandem Annulation Approach †

Synthetic Studies on Tetracyclic Diquinane Lycopodium Alkaloids Magellanine, Magellaninone and Paniculatine

(-)-Magellanine, (+)-magellaninone, and (+)-paniculatine are three natural products isolated from the Lycopodium family that share a unique 6-5-5-6-fused tetracyclic diquinane core skeleton. Several members of this family have potent s anti-inflammatory and acetylcholinesterase-inhibitory properties and are under development for the treatment of Alzheimer's and other neurodegenerative diseases. Several research groups have undertaken the formal and total syntheses of this class of natural products. This review highlights over 20 reported total syntheses of these three alkaloids and the development of synthetic methods for the assembly of their core skeletons.

Enantioselective Total Synthesis of (+)-Sieboldine A and Analogues Thereof

An 11-step enantioselective total synthesis of (+)-sieboldine A (1) has been accomplished from (5R)-methylcyclohex-2-en-1-one (16), in which an intramolecular ketone/ester reductive coupling followed by one-pot acidic treatment to quickly construct the unique oxa-spiroacetal and a TsOH-catalyzed displacement to directly form the characteristic N-hydroxyazacyclononane ring successfully served as the key methodologies. Moreover, several full-skeleton analogues of 1 were also synthesized on the basis of the advanced intermediates, and their inhibitory effects on electric eel acetylcholinesterase were examined.

Unified Total Synthesis of Tetracyclic Diquinane Lycopodium Alkaloids (+)-Paniculatine, (-)-Magellanine, and (+)-Magellaninone

A unified route for the total synthesis of three tetracyclic diquinane Lycopodium alkaloids (+)-paniculatine, (-)-magellanine, and (+)-magellaninone has been accomplished in 13-14 overall steps based on late-stage diverse transformations from an advanced tetracyclic common intermediate. In the established synthesis, quick formation of the two five-membered rings was efficiently achieved by an intramolecular reductive coupling of ketone-carbonyl and ester-carbonyl and an organocatalytic intramolecular Michael addition of aldehyde-derived enamine to an internal enone functionality with satisfactory redox and step economies and excellent stereoselectivities, providing the requisite tricyclic carbo-framework possessing multiple dense stereogenic centers, and an intramolecular reductive amination finally furnished the essential piperidine ring.

Total Synthesis of Huperserratines A and B

Huperserratines A (1) and B (2), two novel macrocyclic Lycopodium alkaloids, possess an aza-12-membered ring. Here, we describe the first total synthesis of these two natural products in 12 steps....

Concise Unified Access to (-)-8-Deoxy-13-dehydroserratinine, (+)-Fawcettimine, (+)-Fawcettidine, and (-)-8-Deoxyserratinine Using a Direct Intramolecular Reductive Coupling

A short, scalable, and collective total synthesis of four fawcettimine-type Lycopodium alkaloids in eight or nine steps is disclosed. A dense multi-small-ring spiro-α-aminocyclopentanone successfully served as the key intermediate, which was directly accessed by a LiDBB-mediated intramolecular reductive coupling of the aliphatic imine and an ester-carbonyl. Compared to those that employ classical Heathcock intermediate(s) containing a nine-membered ring, the new strategy shows the significant improvement of the synthetic step and redox economies as well as excellent stereochemical control.