Continued interest in the bioactive alkaloids led to the isolation of five undescribed alkaloids ( 1 -5 ), ophiorglucidines A -E, and seven known analogues ( 6 -12 ) from the water-soluble fraction of Ophiorrhiza japonica. The structures were elucidated based on spectroscopic data and quantum calculations as well as X-ray crystallographic analysis. The structure of 1 was characterized as a hexacyclic skeleton including a double bridge linking the indole and the monoterpene moieties, which is the first report of a single crystal with this type of structure. Moreover, the inhibitory effect of zwitterionic indole alkaloid glycosides on xanthine oxidase was found for the first time. The alkaloids 2 and 3 , both of which have a pentacyclic zwitterionic system, were more active than the reference inhibitor, allopurinol (IC 50 = 11.1 mu M) with IC 50 values of 1.0 mu M, and 2.5 mu M, respectively. Structureactivity relationships analyses confirmed that the carbonyl group at C-14 was a key functional group responsible for the inhibitory effects of these alkaloids.