Ring natural scaffolds

Krafft and co-workers used olefin metathesis to prepare several inside-outside medium-size rings as scaffolds for natural products synthesis. Reaction of bicyclic lactone 267 with 10 mol % of 4 in refluxing dicholormethane gave the corresponding tricyclic lactone 269 in 88% yield after only two hours. 

Sequential pyrrolidine and hydantoin ring-forming reactions via intramolecular [2+3] cycloaddition have been applied to the stereoselective solid-phase synthesis of conformationally constrained tricyclic triazacyclopenta [C]pentalene scaffold 43 < 1999JOC8342>. These novel compounds 43 share the structural complexity characteristic of certain alkaloid natural products, angular triquinanes. The retrosynthetic analysis is shown in Scheme 87. 

Lycogalic acid (131) and halitulin (132) represent unique analogs (Fig. 8) to the 3,4-diaryl pyrrole scaffold of the natural products previously discussed. Lycogalic acid (131) contains indole rings attached at both C-3 and C-4 of... 

Aryl indole as a G-protein-coupled receptor (GPCR) privileged scaffold. The indole ring is a premier example of a privileged scaffold. The heterocycle is present in a profusion of medicinally important natural products and pharmaceutical substances, and it is associated with an extraordinary manifold of biological... 

Bonnet and Ganesan [12] developed a new route toward the solid-phase synthesis of tetrahydro-P-carboline hydantoins, which appear in a diverse array of biologically active alkaloids. Due to the presence of tetrahydro-P-carbolines and diketo-piperazine ring skeletons in several bioactive natural products, these two scaffolds became attractive targets for developing a combinatorial chemistry program. 

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