3-oxo-rhazinilam: a new indole alkaloid from Rauvolfia serpentina x Rhazya stricta hybrid plant cell cultures

Copper-Catalyzed Annulation of O-Acyl Oximes with Cyclic 1,3-Diones for the Synthesis of 7,8-Dihydroindolizin-5(6H)-ones and Cyclohexanone-Fused Furans

A copper-catalyzed annulation of O-acyl oximes with cyclic 1,3-diones has been developed for the concise synthesis of 7,8-dihydroindolizin-5(6H)-ones and cyclohexanone-fused furans through the substituent-controlled selective radical coupling process. 2-Alkyl cyclic 1,3-diones undergo C-C radical coupling, while 2-unsubstituted cyclic 1,3-diones undergo C-O radical coupling.

Rhazinilam-leuconolam family of natural products: a half century of total synthesis

Covering: 1972 to 2021The rhazinilam family of natural products exhibits a main structure with a stereogenic quaternary carbon and a tetrahydroindolizine core imbedded within a 9-membered macrocycle, imposing axial chirality. This unique architecture combined with their taxol-like antimitotic activities have attracted various attention, especially from synthetic chemists, notably in the past decade. The present review describes the known total and formal syntheses of the members of the rhazinilam family (rhazinilam, rhazinal, leuconolam and kopsiyunnanines), according to the strategy developed.

Access to azonanes via Pd-catalyzed decarboxylative [5 + 4] cycloaddition with exclusive regioselectivity

An efficient approach for the synthesis of azonanes via Pd-catalyzed decarboxylative [5 + 4] cycloaddition has been developed. The reactions feature wide functional group tolerance with exclusive regioselectivity.

Recent progress in the total synthesis of pyrrole-containing natural products (2011–2020)

This review discusses total syntheses of pyrrole-containing natural products over the last ten years, highlighting recent advances in the chemistry of pyrroles in the context of their innate reactivity, and their preparation in complex settings.

Origin of the Diastereoselectivity of the Heterogeneous Hydrogenation of a Substituted Indolizine

In this work, the stereoselective heterogeneous hydrogenation of a tetrasubstituted indolizine was studied. Partial hydrogenation products were obtained in three steps from a substituted pyridine-2-carboxaldehyde prepared from commercial pyridoxine hydrochloride. The hydrogenation of the indolizine ring was shown to be diastereoselective, forming trans-6b and cis-9. Theoretical calculations (ab initio and DFT) were used to rationalize the unusual trans stereoselectivity for 6b, and a keto–enol tautomerism under kinetic control has been proposed as the source of diastereoselectivity.

Gold catalysis in total synthesis – recent achievements

The most recent achievements of gold catalysed transformations applied in total synthesis of natural products are reviewed and analysed.

Biosynthetically inspired divergent approach to monoterpene indole alkaloids: total synthesis of mersicarpine, leuconodines B and D, leuconoxine, melodinine E, leuconolam, and rhazinilam

Inspired by their potential biosynthesis, we have developed divergent total syntheses of seven monoterpene indole alkaloids including mersicarpine, leuconodines B and D, leuconoxine, melodinine E, leuconolam, and rhazinilam, and one unnatural analogue with an unprecedented structural skeleton. The key steps involve a Witkop-Winterfeldt oxidative indole cleavage followed by transannular cyclization. The transannular cyclization product was then converted to the corresponding structural skeletons by pairing its functional groups into different reaction modes.

C-H activation: a complementary tool in the total synthesis of complex natural products

The recent advent of transition-metal mediated C-H activation is revolutionizing the synthetic field and gradually infusing a "C-H activation mind-set" in both students and practitioners of organic synthesis. As a powerful testament of this emerging synthetic tool, applications of C-H activation in the context of total synthesis of complex natural products are beginning to blossom. Herein, recently completed total syntheses showcasing creative and ingenious incorporation of C-H activation as a strategic manoeuver are compared with their "non-C-H activation" counterparts, illuminating a new paradigm in strategic synthetic design.

In vivo monitoring of alkaloid metabolism in hybrid plant cell cultures by 2D cryo-NMR without labelling

Non-invasive measurements of alkaloid metabolism in plant cell suspension cultures of a somatic hybrid from Rauvolfia serpentina Benth. ex Kurz and Rhazya stricta Decaisne were carried out. When cell samples were taken sequentially from a stock feeding experiment, measuring times for in vivo NMR of 40 min were sufficient for following conversions of alkaloids at the natural abundance of 13C. Degradation of ajmaline added to the cells at 1.6 mM concentration to raumacline could be monitored after 96 h on a standard 800 MHz NMR instrument (Avance 800). Feeding vinorine an intermediate of ajmaline biosynthesis at 1.8 mM showed with a 500 MHz CryoProbe that the alkaloid enters two metabolic routes. Vinorine is intracellularly transformed on route I through vellosimine and 10-deoxysarpagine into sarpagine. On route II, the alkaloid is converted by hydroxylation through vomilenine into the glucoside raucaffricine. Intracellular alkaloid concentrations of approximately 500 microM are measurable in vivo with cryogenic NMR technology.

Solid-phase synthesis of 2,3,5-trisubstituted indoles

2,3,5-Trisubstituted indoles are synthesized in three steps starting from resin-bound aniline 2. R1 is introduced by a palladium-mediated coupling of the aryl iodide with terminal alkynes followed by intramolecular cyclization to form the indole core. Acylation at C-3 with an acid chloride in the presence of AlCl(3) catalyst introduces R2. The indole C-5 position is then diversified either by Sonagashira or Suzuki couplings with the aryl bromide. Finally, indole N-1 can be modified by post-cleavage methylation. [reaction: see text]