Proline Ester Enolate Claisen Rearrangement and Formal Total Synthesis of (-)-Cephalotaxine

Homoharringtonine: updated insights into its efficacy in hematological malignancies, diverse cancers and other biomedical applications

HHT has emerged as a notable compound in the realm of cancer treatment, particularly for hematological malignancies. Its multifaceted pharmacological properties extend beyond traditional applications, warranting an extensive review of its mechanisms and efficacy. This review aims to synthesize comprehensive insights into the efficacy of HHT in treating hematological malignancies, diverse cancers, and other biomedical applications. It focuses on elucidating the molecular mechanisms, therapeutic potential, and broader applications of HHT. A comprehensive search for peer-reviewed papers was conducted across various academic databases, including ScienceDirect, Web of Science, Scopus, American Chemical Society, Google Scholar, PubMed/MedLine, and Wiley. The review highlights HHT's diverse mechanisms of action, ranging from its role in leukemia treatment to its emerging applications in managing other cancers and various biomedical conditions. It underscores HHT's influence on cellular processes, its efficacy in clinical settings, and its potential to alter pathological pathways. HHT demonstrates significant promise in treating various hematological malignancies and cancers, offering a multifaceted approach to disease management. Its ability to impact various physiological pathways opens new avenues for therapeutic applications. This review provides a consolidated foundation for future research and clinical applications of HHT in diverse medical fields.

Reductive Oxy-Nazarov Cyclization toward Expedient Construction of a Cyclopenta[1,2-b]pyrrolo[1,2-a]azepine Ring System: Formal Total Syntheses of Stemonamine and Cephalotaxine

Formal total syntheses of stemonamine and cephalotaxine bearing the core cyclopenta[1,2-b]pyrrolo[1,2-a]azepine ring skeleton were achieved. The general synthetic strategy in the synthesis features the reductive oxy-Nazarov cyclization as key step, leading to the versatile construction of N-substituted spiro quaternary stereogenic centers from readily available starting materials.

Enantioselective Total Synthesis of the Cephalotaxus Alkaloid (-)-Cephalotine A

Cephalotine A, a recently isolated Cephalotaxus alkaloid, was first synthesized enantioselectively through three critical reactions. SmI2 -mediated radical cyclization of lactone and aldehyde to forge the final ring system, Chang's iridium-catalyzed C-H amidation to construct pyrrolidone stereoselectively, and Carreria's dual Ir/amine catalyzed allylation to install the vicinal tertiary stereocenters.

Copper-Catalyzed Reductive Ireland-Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates

The copper-catalyzed reductive Ireland-Claisen rearrangement of propargylic acrylates led to 3,4-allenoic acids. The use of silanes or pinacolborane as stoichiometric reducing agents and triethylphosphite as a ligand facilitated the divergent and complementary selectivity for the synthesis of diastereomeric anti- and syn-rearranged products, respectively. Copper-catalyzed reductive Ireland-Claisen rearrangement of allylic 2,3-allenoates proceeded effectively only when pinacolborane was used as a reductant to generate various 1,5-dienes in excellent yields and with good diastereoselectivities in some cases. Mechanistic studies showed that the silyl and boron enolates, rather than the copper enolate, underwent a stereospecific rearrangement via a chairlike transition state to afford the corresponding Claisen rearrangement products.

Gold(I)-Catalyzed Cyclization-3-Aza-Cope-Mannich Cascade and Its Application to the Synthesis of Cephalotaxine

The discovery of a new gold(I)-catalyzed cascade reaction involving cyclization onto a vinylammonium, 3-aza-Cope rearrangement, and Mannich cyclization is reported. A variety of fused nitrogen heterocycles were prepared from simple cyclic tertiary amines using 1-5 mol % of a AuCl(PPh₃)/Ag[C₅(CN)₅] cocatalyst system. The developed reaction was used in a study aimed at synthesizing cephalotaxine. A five-step operation from norhydrastinine provided demethylcephalotaxinone in 39.1% overall yield, which was transformed to (-)-cephalotaxine in two steps.

Collective Asymmetric Total Synthesis of C-11 Oxygenated Cephalotaxus Alkaloids

While numerous studies pertaining to the total synthesis of Cephalotaxus alkaloids have been reported, only two strategies have been reported to date for the successful synthesis of the C-11 oxygenated subset, due to the additional synthetic challenge posed by the remote C-11 stereocenter. Herein, we report the collective asymmetric total synthesis of C-11 oxygenated Cephalotaxus alkaloids using a chiral proline both as a starting material and as the only chirality source. A tetracyclic advanced intermediate was synthesized in a highly stereoselective manner from l-proline in 8 steps involving sequential chirality transfer steps such as a diastereoselective N-alkylation, stereospecific Stevens rearrangement and intramolecular Friedel-Crafts reaction via an unusual O-acyloxocarbenium intermediate. From a common intermediate, the asymmetric total synthesis of six C-11 oxygenated Cephalotaxus alkaloids was completed by a series of oxidation state adjustments.

A modular and divergent approach to spirocyclic pyrrolidines

An efficient three-step sequence to afford a valuable class of spirocyclic pyrrolidines is reported. A reductive cleavage/Horner-Wadsworth-Emmons cascade facilitates the spirocyclisation of a range of isoxazolines bearing a distal β-ketophosphonate. The spirocyclisation precursors are elaborated in a facile and modular fashion, via a [3 + 2]-cycloaddition followed by the condensation of a phosphonate ester, introducing multiple points of divergence. The synthetic utility of this protocol has been demonstrated in the synthesis of a broad family of 1-azaspiro[4,4]nonanes and in a concise formal synthesis of the natural product (±)-cephalotaxine.