Synthesis of the dipyrrolopyrazinone core of dibromophakellstatin and related marine alkaloids
摘要:
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.
Study on the absolute configuration of (−)-palau’amine
作者:Thomas Lindel、Delphine E.N. Jacquot、Michael Zöllinger、Robin B. Kinnel、Shayna McHugh、Matthias Köck
DOI:10.1016/j.tetlet.2010.09.148
日期:2010.12
absolute stereochemistry of the immunosuppressive pyrrole–imidazole alkaloid (−)-palau’amine from the marinesponge Stylotella aurantium is analyzed by CD spectroscopy. With the help of a series of model compounds it is shown that the CD spectrum of (−)-palau’amine can be explained based on the assumption that the pyrrolopyrazinone partial structure is planar in 2,2,2-trifluoroethanol (TFE). Surprisingly