Total Synthesis of the Diterpenoid Alkaloid Arcutinidine Using a Strategy Inspired by Chemical Network Analysis.

Arcutinidine and other arcutinidine-type diterpenoid alkaloids feature an intricate polycyclic, bridged framework with unusual connectivity. A chemical network analysis approach to the arcutane skeleton enabled the identification of highly simplifying retrosynthetic disconnections, which indicated that the caged structure could arise from a simpler fused ring system. On this basis, a total synthesis of arcutinidine is reported herein, featuring an unprecedented oxopyrrolium Diels-Alder cycloaddition which furnishes a key tetracyclic intermediate. In addition, the synthesis utilizes a diastereoselective oxidative dearomatization/cycloaddition sequence and a SmI2-mediated C-C coupling to forge the bridged framework of the natural products. This synthetic plan may also enable future investigations into the biosynthetic relationships between the arcutanes, the related diterpenoid atropurpuran, and other diterpenoid alkaloids.

Development of the Vinylogous Pictet-Spengler Cyclization and Total Synthesis of (±)-Lundurine†A.

A novel vinylogous Pictet-Spengler cyclization has been developed for the generation of indole-annulated medium-sized rings. The method enables the synthesis of tetrahydroazocinoindoles with a fully substituted carbon center, a prevalent structural motif in many biologically active alkaloids. The strategy has been applied to the total synthesis of (±)-lundurine A.

Structure-guided development of specific pyruvate dehydrogenase kinase inhibitors targeting the ATP-binding pocket.

Pyruvate dehydrogenase kinase isoforms (PDKs 1-4) negatively regulate activity of the mitochondrial pyruvate dehydrogenase complex by reversible phosphorylation. PDK isoforms are up-regulated in obesity, diabetes, heart failure, and cancer and are potential therapeutic targets for these important human diseases. Here, we employed a structure-guided design to convert a known Hsp90 inhibitor to a series of highly specific PDK inhibitors, based on structural conservation in the ATP-binding pocket. The key step involved the substitution of a carbonyl group in the parent compound with a sulfonyl in the PDK inhibitors. The final compound of this series, 2-[(2,4-dihydroxyphenyl)sulfonyl]isoindoline-4,6-diol, designated PS10, inhibits all four PDK isoforms with IC50 = 0.8 µM for PDK2. The administration of PS10 (70 mg/kg) to diet-induced obese mice significantly augments pyruvate dehydrogenase complex activity with reduced phosphorylation in different tissues. Prolonged PS10 treatments result in improved glucose tolerance and notably lessened hepatic steatosis in the mouse model. The results support the pharmacological approach of targeting PDK to control both glucose and fat levels in obesity and type 2 diabetes.

Atropurpuran - Missing Biosynthetic Link Leading to the Hetidine and Arcutine C20-Diterpenoid Alkaloids or an Oxidative Degradation Product?

A possible biosynthetic link between atropurpuran, the hetidine diterpenoid alkaloids and the alkaloid arcutine and congeners is proposed. The feasibility of aspects of this biosynthesis, especially key 1,2-rearrangements, have been examined computationally.

Studies on C20-diterpenoid alkaloids: synthesis of the hetidine framework and its application to the synthesis of dihydronavirine and the atisine skeleton.

The full details of a synthesis of the hetidine framework of the C20-diterpenoid alkaloids and its conversion to the atisine core structure are reported. The application of the hetidine framework to the synthesis of dihydronavirine, which is the formal reduction product of the natural product navirine, is also described. Key to the success of these studies is the use of a Ga(III)-catalyzed cycloisomerization reaction of alkynylindenes to prepare a [6-7-6] framework that was advanced to the hetidine skeleton. Furthermore, a Michael/aldol sequence was developed for the construction of the bicyclo[2.2.2] framework that is characteristic of the hetidines and atisines.

Construction of Enantiopure Taxoid and Natural Product-like Scaffolds Using a C-C Bond Cleavage/Arylation Reaction.

An approach to construct enantiopure complex natural product-like frameworks, including the first reported synthesis of a C17 oxygenated taxoid scaffold, is presented. A palladium-catalyzed C-C activation/cross-coupling is utilized to access these structures in a short sequence from (+)-carvone; the scope of this reaction is explored.