ORGN 567 |
Forging unstable multicyclic frameworks of the kedarcidin chromophore: Total synthesis in sight
| Martin J. Lear, Yasuhito Koyama, Fumihiko Yoshimura, Isao Ohashi, and Masahiro Hirama. Department of Chemistry, Tohoku University, Graduade School of Science, Aza Aramaki, Sendai 980 8578, Japan |
| Several advanced approaches to the synthesis of the kedarcidin chromophore will be presented. Besides new and efficient gram-scale syntheses of the diyne and cyclopentene components, the inversion of the C4-stereocenter and use of C13-OMOM protection, resulted in an efficient synthesis of the multicyclic ansamacrolide framework of the kedarcidin chromophore; this tactical change allowed for the Sonogashira coupling step to proceed in 89 % yield (cf. 45 % before) with complete atropselectivity and for the b-C8 mesylate to be sterically allowed within the transannular cavity of the carbon-framework of the kedarcidin chromophore aglycon. Further work was geared towards the successful developement of anionic, cerium-acetylide procedures to form unstable, nine-membered diyne cores within pre-existing ansamacrolide-naphthoamide frameworks. These developments including highly advanced stages towards the kedarcidin chromophore and critical comparison of results will be discussed. 
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