Synthetic study of spiroiridal triterpenoids: construction of functionalized spiro[4.5]decane skeleton using Claisen rearrangement of 2-(alkenyl)dihydropyran

Cytotoxic iridal-type triterpenoids from Iris tectorum

“…8 Various biological activities of these substances including cytotoxicity, [9][10] ichthyotoxicity, 11 antiplasmodial, 12 and PKC activation 13 have been reported, making them attractive targets for chemical synthesis. [14][15][16] In our continuing search for new bioactive iridals, 5 seven new iridals (1)(2)(3)(4)(5)(6)(7) were isolated from the ethanol extract of rhizomes of I. tectorum, together with three known analogues (8)(9)(10). We report herein the isolation, structure elucidation and cytotoxic activities of these compounds (Fig.…”

Toward a Synthesis of Fawcettimine-Type Lycopodium Alkaloids: Stereocontrolled Synthesis of a Functionalized Azaspirocycle Precursor

“…Azacyclononane of 1 would be constructed from cyclohexene 2 through the intramolecular Mitsunobu reaction . On the basis of previous results, , the cis -configured stereogenic centers of 2 would be established by a Claisen rearrangement of 3 through a boat-like transition state ( vide infra ). As the Claisen rearrangement of alkenyl dihydropyrans is sensitive to an environment of the allylic substituent (a triethylsiloxy group in this case), one of the C13-epimers of the Claisen precursors [( S )-epimer, epi - 3b , as shown in Scheme ] is expected to undergo the Claisen rearrangement only very slowly.…”

“…Herein, we report the stereocontrolled synthesis of a new azaspirocycle precursor of the fawcettimine-type Lycopodium alkaloids, which bears all of the requisite functionality and core stereogenic centers in their desired configurations, as well as a carbon–carbon double bond between C8 and C15 for introduction of the stereogenic center at C15 , and oxygen functionality at C8 or C15 . Construction of the azaspirocyclic skeleton was achieved using an efficient cascade Wacker-allylation sequence and a highly stereoselective Claisen rearrangement of a functionalized alkenyl dihydropyran system, previously developed in this group, as key reactions. , Azaspirocycle 1 is expected to be a versatile common precursor for the fawcettimine-type Lycopodium alkaloids…”

Polycycloiridals with a Cyclopentane Ring from Iris tectorum

“…To date, approximately 80 naturally occurring iridals have been reported . These molecules exhibit various biological properties including cytotoxicity, , ichthyotoxicity, antiplasmodial effects, and PKC activation. , These fascinating structures have promising biological activities, resulting in several synthesis efforts for this class of compounds. − In continuing efforts toward the discovery of structurally intriguing iridals from this plant, − trace amounts of polycycloiridals E–J ( 1 – 6 ), together with the known spirioiridotectal D ( 7 ), were isolated during a large-scale re-extraction of the rhizomes of I. tectorum . Compounds 1 – 6 possessed a unique cyclopentane ring resulting from cyclization of the homofarnesyl side chain.…”