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Updated: Aug 15, 2026

A Direct, Early Stage Guanidinylation Protocol for the Synthesis of Complex Aminoguanidine-containing Natural Products
Published on: September 9, 2016
Absolute stereochemistry of citrinadins a and B from marine-derived fungus
Takao Mugishima1, Masashi Tsuda, Yuu Kasai
1Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
Abstract:
[Structure: see text]. Citrinadin A (2) is a pentacyclic indolinone alkaloid isolated from the cultured broth of a fungus, Penicillium citrinum, which was separated from a marine red alga. The absolute stereochemistry of the pentacyclic core in 2 and its new congener, citrinadin B (1), was elucidated by analysis of the ROESY spectrum for the chlorohydrin derivative (3) of 1 as well as comparison of the electronic circular dichroism (ECD) spectra for 1 and 2 with those of known spirooxiindole alkaloids. On the other hand, the absolute configuration at C-21 bearing an epoxide ring was assigned as S by comparison of the vibrational circular dichroism (VCD) spectra of 1 with those of model compounds 2S- and 2R-2,3-epoxy-3,3-dimethyl-1-phenylpropan-1-one (4a and 4b, respectively).
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In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
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