New C20-diterpenoid alkaloids from Aconitum vilmorrianum and structural revision of 2-O-acetylorochrine and orochrine

The diterpenoid alkaloids

The diterpenoid alkaloids are a family of extremely important natural products that have long been a research hotspot due to their myriad of intricate structures and diverse biological properties. This chapter systematically summarizes the past 11 years (2009-2019) of studies on the diterpenoid alkaloids, including the "so-called" atypical ones, covering the classification and biogenetic relationships, phytochemistry together with 444 new alkaloids covering 32 novel skeletons and the corrected structures, chemical reactions including conversion toward toxoids, synthetic studies, as well as biological activities. It should be noted that the synthetic studies, especially the total syntheses of various diterpenoid alkaloids, are for the first time reviewed in this treatise. This chapter, in combination with our four previous reviews in volumes 42, 59, 67, and 69, will present to the readers a more completed and updated profile of the diterpenoid alkaloids.

Chemistry and biological activities of hetisine-type diterpenoid alkaloids

Hetisine-type C₂₀-diterpenoid alkaloids (DAs) are one of the most important DA subtypes. During the past decades, a total of 157 hetisine-type DAs were obtained from plants from seven genera in three families, most of which were isolated from the genera Aconitum and Delphinium in the Ranunculaceae family. Structurally, hetisine-type DAs are characterized by a heptacyclic hetisane skeleton formed by the linkage of C(14)–C(20) and N–C(6) bonds in an atisine-type DA, and their structural diversity is created by the states of the N atom and various substituents. Pharmacological studies have revealed a wide range of pharmacological actions for hetisine-type DAs, including antiarrhythmic, antitumor, antimicrobial and insecticidal activities, as well as effects on peripheral vasculature, which are closely related to their chemical structures. In particular, the prominent antiarrhythmic effects and low toxicity of hetisine-type DAs highlight their potential in antiarrhythmic drug discovery. Hetisine-type DAs with diverse bioactivities are promising lead structures for further development as commercial agents in medicine.

Natural hetisine-type C₂₀-diterpenoid alkaloids with diverse structures showed multiple pharmacological activities, indicating great potential in drug discovery.

Structural diversity, bioactivities, and biosynthesis of natural diterpenoid alkaloids

Covering: 2009 to 2018. Diterpenoid alkaloids, originating from the amination of natural tetracyclic diterpenes, are a diverse class of compounds having complex structural features with many stereocenters. The important pharmacological activities and structural complexity of the diterpenoid alkaloids have long interested scientists due to their medicinal uses, infamous toxicity, and unique biosynthesis. Since 2009, 373 diterpenoid alkaloids, assigned to 46 skeletons, have been isolated and identified from plants mostly in the Ranunculaceae family. The names, classes, molecular weight, molecular formula, NMR data, and plant sources of these diterpene alkaloids are collated here. This review will be a detailed update of the naturally occurring diterpene alkaloids reported from the plant kingdom from 2009-2018, providing an in-depth discussion of their diversity, biological activities, pharmacokinetics, toxicity, application, evolution, and biosynthesis.

Classification, Toxicity and Bioactivity of Natural Diterpenoid Alkaloids

Diterpenoid alkaloids are natural compounds having complex structural features with many stereo-centres originating from the amination of natural tetracyclic diterpenes and produced primarily from plants in the Aconitum, Delphinium, Consolida genera. Corals, Xenia, Okinawan/Clavularia, Alcyonacea (soft corals) and marine sponges are rich sources of diterpenoids, despite the difficulty to access them and the lack of availability. Researchers have long been concerned with the potential beneficial or harmful effects of diterpenoid alkaloids due to their structural complexity, which accounts for their use as pharmaceuticals as well as their lousy reputation as toxic substances. Compounds belonging to this unique and fascinating family of natural products exhibit a broad spectrum of biological activities. Some of these compounds are on the list of clinical drugs, while others act as incredibly potent neurotoxins. Despite numerous attempts to prepare synthetic products, this review only introduces the natural diterpenoid alkaloids, describing 'compounds' structures and classifications and their toxicity and bioactivity. The purpose of the review is to highlight some existing relationships between the presence of substituents in the structure of such molecules and their recognised bioactivity.

Structure, property, biogenesis, and activity of diterpenoid alkaloids containing a sulfonic acid group from Aconitum carmichaelii

Three new C20-diterpenoid alkaloids with a sulfonic acid unit, named aconicarmisulfonines B and C (1 and 2) and chuanfusulfonine A (3), respectively, were isolated from the Aconitum carmichaelii lateral roots ("fu zi" in Chinese). Structures of 1-3 were determined by spectroscopic data analysis. Intriguing chemical properties and reactions were observed for the C20-diterpenoid alkaloids: (a) specific selective nucleophilic addition of the carbonyl (C-12) in 1 with CD3OD; (b) interconversion between 1 and 2 in D2O; (c) stereo- and/or regioselective deuterations of H-11α in 1-3 and both H-11α and H-11β in aconicarmisulfonine A (4); (d) TMSP-2,2,3,3-d 4 promoted cleavage of the C-12-C-13 bond of 4 in D2O; (e) dehydrogenation of 4 in pyridine-d 5, and (f) Na2SO3-assisted dehydrogenation and N-deethylation of songorine (5, a putative precursor of 1-4). Biogenetically, 1 and 2 are correlated with 4, for which the same novel carbon skeleton is proposed to be derived from semipinacol rearrangements via migrations of C-13-C-16 and C-15-C-16 bonds of the napelline-type skeleton, respectively. Meanwhile, 3 is a highly possible precursor or a concurrent product in the biosynthetic pathways of 1, 2, and 4. In the acetic acid-induced mice writhing assay, at 1.0 mg/kg (i.p.), compounds 1, 2, 5, 5a, and 5b exhibited analgesic effects against mice writhing.

Pseudo-Natural Products, Some Artefacts Formed during the Isolation of Terpenoids

The formation of artefacts during the isolation, purification and characterisation of terpenoids is reviewed.