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, [a] D values, and HPLC analysis of 2b, 2c, and natural eudistomidin B. (C) 2010 Elsevier Ltd. All rights reserved.