Chiroptical Analysis of Marine Sponge Alkaloids Sharing the Pyrrolopyrazinone Core
作者:Delphine E. N. Jacquot、Peter Mayer、Thomas Lindel
DOI:10.1002/chem.200305392
日期:2004.3.5
A systematic experimental study has been conducted on the chiroptical properties of bi- and tricyclic pyrrolopyrazinones, which occur as the core in a variety of marine pyrrole-imidazole alkaloids, such as the immunosuppressive palau'amine. On the basis of the chiral-pool synthesis of conformationally fixed dipyrrolopyrazinones, it was possible to predict the CD spectrum of (-)-dibromophakellin above
The dipyrrolopyrazinone (ABC) core of the phakelline-type pyrrole-imidazole alkaloids from marine sponges was synthesized starting from L-prolinol and 2-trichloroacetylated pyrroles. On oxidation of the condensation product with IBX, immediate cyclization occurs. It was found that the presence of a bromine substituent in the 8-position of the resulting tricyclic N,O-hemiacetal exclusively favors the cis relative configuration at the stereogenic centers C10 and C10a. Via an intermediate tertiary N-acyliminium ion, the pyrazinone core was dihydroxylated by treatment with m-CPBA in the presence of water. The simultaneous functionalization of the C10 and C10a positions is an important step towards the synthesis of the cytotoxic natural product dibromophakellstatin (C) 2002 Elsevier Science Ltd. All rights reserved.
Hypervalent Iodine-Mediated Vicinal Syn Diazidation: Application to the Total Synthesis of (±)-Dibromophakellstatin
作者:Raymond Chung、Eunsun Yu、Christopher D. Incarvito、David J. Austin
DOI:10.1021/ol0490532
日期:2004.10.1
[reaction: see text] The totalsynthesis of (+/-)-dibromophakellstatin is described. The molecule is constructed from a key syn-diazide, formed by a hypervalent iodine-mediated diazidation of a dihydrodipyrrolopyrazinone ring structure.