Synthesis of the Proposed Structures of Parvistemoamide and Their Transformations to Stemoamide Derivatives

Total syntheses of the parvistemoline alkaloids enabled by stereocontrolled Ir/Pd-catalyzed allylic alkylation

The functionalized polycycle with densely contiguous tertiary stereocenters is a formidable challenge in synthesizing the parvistemoline family of Stemona alkaloids. We herein report their catalytic, asymmetric total syntheses in 13-14 steps from commercially available 2-(methoxycarbonyl)-pyrrole, featuring the development and deployment of an Ir/Pd-synergistically-catalyzed allylation of α-non-substituted keto esters with secondary aryl-substituted alcohols, stereodivergently accessible to four stereoisomers. Using chiral Pd-enolate and Ir π-allyl complex under neutral conditions, no epimerization occurs. Additionally, the other two adjacent stereogenic centers can be installed diastereoselectively by Zn(BH4)2-promoted reduction and Krische's Ir-catalyzed 2-(alkoxycarbonyl)allylation. Oxy-Michael addition delivered the fused tetrahydrofuran-γ-lactone scaffold. At the later stage, hydrogenation or oxidation of pyrrole moiety furnished groups of tetrahydropyrrole and pyrrolidone. Finally, vinylogous Mannich reaction of an in situ generated iminium ion or Krische's Ir-catalyzed 2-(alkoxycarbonyl)allylation of aldehyde installed the monocyclic lactone for parvistemonine (2) and didehydroparvistemonine (3), respectively.

Targeted Metabolic Investigation of Ligandrol and Analytical Methods Validation for Its Main Long-term Metabolite

Prompted by the need for related analytical reference material in the frame of the fight against doping in sports, synthetic efforts towards the main long-term bishydroxylated metabolite (LGD-LTM1) of the nonsteroidal selective androgen receptor modulator (SARM) ligandrol have produced related derivatives that were exploited for a targeted metabolite analysis of urine samples obtained in the course of previous excretion studies of this SARM. Further clarifying ligandrol's metabolic profile, the availability of synthetic reference material permitted the structural elucidation of a previously reported pyrrolidinone-type metabolite and revealed its potential analytical utility as an additional long-term marker. Moreover, synthetic reference material enabled the comparison and validation of liquid chromatography coupled with mass spectrometry (LC-MS)-based and gas chromatography coupled with mass spectrometry (GC-MS)-based detection and identification methods focusing on the LGD-LTM1 marker.

Asymmetric Total Synthesis of Four Stemona Alkaloids

Asymmetric total syntheses of four Stemona alkaloids were accomplished, and among them, bisdehydrostemoninine A and stemoninine A were synthesized for the first time. Notably, these four alkaloids were divergently synthesized from a common tetracyclic intermediate, which was easily obtained from a known compound. Friedel-Crafts acylation was employed to introduce the key side chain at position C3 of Stemona alkaloids.

Computer-aided key step generation in alkaloid total synthesis

Efficient chemical synthesis is critical to satisfying future demands for medicines, materials, and agrochemicals. Retrosynthetic analysis of modestly complex molecules has been automated over the course of decades, but the combinatorial explosion of route possibilities has challenged computer hardware and software until only recently. Here, we explore a computational strategy that merges computer-aided synthesis planning with molecular graph editing to minimize the number of synthetic steps required to produce alkaloids. Our study culminated in an enantioselective three-step synthesis of (-)-stemoamide by leveraging high-impact key steps, which could be identified in computer-generated retrosynthesis plans using graph edit distances.

Strategies for the synthesis of Stemona alkaloids: an update

Covering: 2009 to 2022The Stemona alkaloids, which are found in plant species from the family Stemonaceae, represent a tremendously large and structurally-diverse family of natural products. This review presents and discusses a selection of case studies, grouped by alkaloid class, that showcase the key strategies and overall progress that has been made in the synthesis of Stemona alkaloids and related compounds since 2009. Structural reassignments that have been reported over this period are also identified where necessary.

Structural Revision of the Stemona Alkaloids Tuberostemonine O, Dehydrocroomines A and B, and Dehydrocroomine

The structural revision of four Stemona alkaloids from Stemona tuberosa is reported. The misassignment of the tuberostemonine O structure (1) was recognized when a new alkaloid, tuberostemonine P, was isolated and unambiguously assigned structure 1 in this work. Reinvestigation of the spectroscopic data and NMR calculations led to the revised structure 1a for tuberostemonine O. The structural misassignment of dehydrocroomine A as 2 was corrected by reinterpreting the X-ray crystal structure, which was consistent with 2a. The structural reassignments of dehydrocroomine B (3 to 3a) and dehydrocroomine (4 to 4a) were confirmed by X-ray crystallography and NMR calculations, respectively.

Structural Revision of Parvistemoamide: Informing Biosynthetic Proposals of Stemona Alkaloids

The natural product parvistemoamide was isolated in 1991 and has ostensibly eluded synthesis. Its distinctive assigned structure represents the first and only Stemona alkaloid within its class. For over 30 years, this structure has influenced biosynthetic proposals concerning this family of natural products. Following synthetic studies and comprehensive analysis of relevant literature, a revised structure of parvistemoamide is proposed that is consistent with the fundamental Stemona alkaloid stemoamide.

Total syntheses of seven stemoamide-type Stemona alkaloids

Six Stemona alkaloids were synthesized racemically using stemoamide, obtained via a cascade cyclization or our reported transannular cyclization of parvistemoamide, as the common intermediate.

Asymmetric Total Syntheses of Five Pyrrole-Type Stemona Alkaloids

The asymmetric total syntheses of five pyrrole-type Stemona alkaloids and two stereoisomers were accomplished, among which 3-n-butylneostemonine and bisdehydroneostemonine were synthesized for the first time, and the NMR data of...

Recent Advances in the Transformations of Different Types of Stemona Alkaloids

In recent years, researches on the total syntheses of Stemona alkaloids with different 5/7 bicyclic systems have attracted increasing attention, and the development momentum in this field has gradually changed...

Ir-Catalyzed Asymmetric Total Syntheses of Bisdehydrotuberostemonine D, Putative Bisdehydrotuberostemonine E and Structural Revision of the Latter

The first total syntheses of bisdehydrotuberostemonine D (8) and putative bisdehydrotuberostemonine E (9), two novel pyrrole Stemona alkaloids, along with the synthesis of bisdehydrotuberostemonine (3) have been completed in 12-13 steps. Our strategy harnesses the power of transition-metal-catalyzed reactions employing Ir, Ru, and Pd, in particular Ir-catalyzed asymmetric allylation of aldehydes, two distinct protocols recently developed by Carreira and Krische, respectively. The threefold use of Ir catalysis, first in the stereodivergent construction of two contiguous stereocenters at C (9,10) and then in rapid formation of the two γ-butyrolactone motifs, enabled the route's efficiency. Through this work, the originally assigned structure of bisdehydrotuberostemonine E (9) should be revised as 18α-bisdehydrotuberostemonine D (8*).