Eudistomidin G, a new beta-carboline alkaloid from the Okinawan marine tunicate Eudistoma glaucus and structure revision of eudistomidin B.

A new beta-carboline alkaloid, eudistomidin G (1), has been isolated from the Okinawan marine tunicate Eudistoma glaucus, and the structure was elucidated from spectroscopic data. Furthermore, the structure of eudistomidin B (2), which has been isolated from the same tunicate, was revised from 2a to 2b by detailed analyses of spectroscopic data. Asymmetric synthesis of the revised structure (2b) of eudistomidin B (2) and its (1S,10S)-diastereomer (2c) has been accomplished with the Noyori catalytic asymmetric hydrogen-transfer reaction. The absolute configuration of eudistomidin B (2) was confirmed to be 2b possessing (1R,10S)-configuration, from comparison of the (1)H NMR data, CD spectra, [alpha](D) values, and HPLC analysis of 2b, 2c, and natural eudistomidin B. 2010 Elsevier Ltd. All rights reserved.