Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 15, Issue 32, Pages 7922-7929Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200900793
Keywords
alkaloids; amino acids; lactams; natural products; total synthesis
Categories
Funding
- The Ministero dell'Istruzione, dell'Universita e della Ricerca [FIRB RBNE03LF7X]
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A total synthesis of the tripeptide alkaloid (-)-chaetominine (1) was achieved in 9.3% overall yield starting from commercially available D-tryptophan methyl ester, based on a short and straightforward (nine steps) sequence. The early stage introduction (first step) of the quinazolinone moiety and the late stage introduction (penultimate step) of the hydroxy group allowed a synthetic strategy devoid of protective groups. The key step of the process is the a-c tricyclic ring construction via an unprecedented NCS-mediated N-acyl cyclization on an indole ring to give tetrahydro-1H-pyrido[2,3-b]indole 11. In the penultimate step, oxidation of the tetracyclic intermediate 14 with oxaziridine 15 gave only one of the four possible diastereoisomers, the cis-diastereoisomer 16 resulting from the attack of the oxaziridine to the double bond face opposite to the c-d ring substituents. In the last step, the complete stereocontrol of the Et3SiH/TFA reduction of compound 16, probably involving a N-acyli-minium ion, can be attributed to ring constrain, which forces the b-c ring junction in the more stable cis-orientation. (-)-Chaetominine (1) showed a negligible inhibitory activity on several cancer cell lines.
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