Total Synthesis of Indole Alkaloids and Natural Products

Total synthesis of indole alkaloids and related natural products remains a cornerstone of contemporary organic chemistry, combining intricate retrosynthetic planning with innovative reaction design. These efforts aim not only to recreate complex molecular architectures seen in nature but also to enable structural diversification, mechanistic insight and practical access to biologically active compounds. Indole alkaloids span myriad structural families—from simple β-carbolines to polycyclic sarpagine, ajmaline and koumine scaffolds—and exhibit activities ranging from anticancer to antimalarial. Recent strategies emphasise redox economy, protecting-group minimisation and cascade cyclisations to streamline synthetic routes. Developments in asymmetric catalysis, photoredox chemistry and radical cyclisation have further enriched the toolkit, allowing for stereocontrolled assembly of challenging ring systems and quaternary centres. The global significance of these syntheses is underscored by their contribution to drug discovery, sustainable chemistry and our understanding of biosynthetic pathways.

Research from Nature Portfolio

Recent studies have dramatically advanced the efficiency and scope of total syntheses for monoterpenoid indole alkaloids. A novel four-step sequence combining a Bischler–Napieralski cyclisation with a homo-Mannich reaction has delivered the tetracyclic sarpagine core from simple tryptophan esters in a protecting-group-free and redox-economic manner, enabling rapid access to diverse analogues and revealing promising anticancer leads through ferroptosis induction. In parallel, a structure-units-oriented approach has realised a unified asymmetric route to sarpagine, ajmaline and koumine type frameworks. Key innovations include a new Mannich-type cyclisation to forge a shared indole-fused azabicyclo[3.3.1]nonane intermediate, SmI₂-mediated E-ring fusion, stereoselective olefinations and an iodo-induced cyclisation to establish adjacent quaternary centres, culminating in the collective synthesis of fourteen natural alkaloids for the first time.

Total Synthesis of Indole Alkaloids and Natural Products publication trend

The graph below shows the total number of articles in total synthesis of indole alkaloids and natural products across all publications each year (not limited to Nature Index journals).

Technical terms

Total synthesis: Complete chemical construction of a complex natural product from simple starting materials.

Indole alkaloid: A class of natural products containing an indole core often derived from tryptophan and characterised by diverse biological activities.

Bischler–Napieralski reaction: Cyclodehydration of β-aryl ethylamides to form dihydroisoquinolines.

Homo-Mannich reaction: Reaction of cyclopropanols with imines to form new C–C bonds via ring opening.

Pictet–Spengler reaction: Acid-mediated condensation of β-arylethylamines with carbonyls followed by cyclisation to yield tetrahydroisoquinolines or β-carbolines.

Organocatalysis: Use of small organic molecules as catalysts to induce stereocontrol in chemical transformations.

SmI₂-mediated coupling: Reductive coupling reactions promoted by samarium(II) iodide, useful for forming carbon–carbon bonds in complex settings.

Redox economy: Strategic minimisation of changes in oxidation states during a synthetic sequence to improve efficiency.

References

1. A Bischler-Napieralski and homo-Mannich sequence enables diversified syntheses of sarpagine alkaloids and analogues. Nature Communications (2023).
2. Structure units oriented approach towards collective synthesis of sarpagine-ajmaline-koumine type alkaloids. Nature Communications (2022).
3. A genetic optimization strategy with generality in asymmetric organocatalysis as a primary target. Chemical Science (2024).
4. The Pictet-Spengler Reaction Updates Its Habits. Molecules (2020).
5. Unified Total Synthesis of Pyrroloazocine Indole Alkaloids Sheds Light on Their Biosynthetic Relationship. Journal of the American Chemical Society (2018).