- Total Synthesis of Resiniferatoxin Enabled by Radical-Mediated Three-Component Coupling and 7-endo Cyclization
-
Resiniferatoxin (1) belongs to a daphnane diterpenoid family and has strong agonistic effects on TRPV1, a transducer of noxious temperature and chemical stimuli. The densely oxygenated trans-fused 5/7/6-tricarbocycle (ABC-ring) of 1 presents a daunting challenge for chemical synthesis. Here we report the development of a novel radical-based strategy for assembling 1 from three components: A-ring 9, allyl stannane 18b, and C-ring 17b. The 6-membered 17b, prepared from d-ribose derivative 19, was designed to possess the caged orthoester structure with α-alkoxy selenide as a radical precursor. Upon treatment of 17b with 18b, 9, and V-40, the potently reactive α-alkoxy bridgehead radical was generated from 17b and then sequentially coupled with 9 and 18b to yield 16b. This first radical reaction formed the hindered C9,10-linkage between the A and C-rings and extended the C4-chain on the A-ring in a stereoselective fashion. After derivatization of 16b into 15, the remaining 7-membered B-ring was cyclized in the presence of n-Bu3SnH and V-40 by utilizing the xanthate on the C-ring as the radical precursor and the allylic dithiocarbonate as the terminator. The second radical reaction thus enabled not only the 7-endo cyclization but also construction of the C8-stereocenter and the C6-exo olefin. Tricycle 14 was elaborated into the targeted 1 by a series of highly optimized chemoselective reactions. The present total synthesis of 1 demonstrates the advantages of radical reactions for linking hindered bonds within carbocycles without damaging preexisting functionalities, thereby offering a new strategic design for multistep target-oriented synthesis.
- Hashimoto, Satoshi,Katoh, Shun-Ichiro,Kato, Takehiro,Urabe, Daisuke,Inoue, Masayuki
-
p. 16420 - 16429
(2017/11/22)
-
- Bisnorsesquiterpenoids from Euphorbia resinifera Berg. and an expeditious procedure to obtain resiniferatoxin from its fresh latex
-
The fresh latex of cultivated E. resinifera Berg. is a convenient source of the ultrapotent vanilloid resiniferatoxin, and a transesterification-reesterification procedure that substantially alleviates the hazards associated with the direct isolation of this obnoxious diterpenoid has been developed. Various known phorboid constituents of the diterpenoid fraction were obtained in pure form and have been spectroscopically characterized for the first time, while the non-diterpenoid fraction of the latex gave, besides some common triterpenoids, three new bisnorsesquiterpenes of the dihydroionol type. The structures of these compounds were established through a combination of spectroscopic data and chemical reactions.
- Fattorusso, Ernesto,Lanzotti, Virginia,Taglialatela-Scafati, Orazio,Tron, Gian Cesare,Appendino, Giovanni
-
-
