The Chemistry and Biology of Lycopodium Alkaloids

Lycopodiales, an order comprising 388 distinct species, is the source of Lycopodium alkaloids (LAs), a group of naturally occurring alkaloids that share a common biosynthesis and structural attributes. These remarkable organisms are considered vestiges of ancient ferns, with fossil evidence dating their existence back to an impressive 300 million years. LAs usually are tricyclic or tetracyclic compounds with C16N or C16N2 skeleton. But then there are also have a few C11N, C15N, C15N2, C22N2, and C27N3 skeleton. LAs have attracted much scientific attention because of their important biological activities related to acetylcholinesterase and unique structural characteristics. From 1881 to December 2023, there are 593 LAs from 49 species of Lycopodiales have been reported. Because the total amount of LAs is nearly five times that of 1994, the classification and group allocation of some newly isolated LAs is often challenging and not unambiguous by Ayer's simple classification. This review makes a more systematic and detailed classification for it and provides extensive coverage of naturally occurring LAs discovered from 1881 to December 2023. Until now, there is no comprehensively summary of biological activity of the LAs. This review is the first time covered the biological activity of the all LAs.

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.