Structural Revision of a Naphthodipyranodione from Gentian Root and its Degradation Pathway from Gentiopicroside.

Based on NOE experiments, the structure of naphthodipyranodione from Gentianaceae plants was revised to 1,2-dihydro-4H,6H,8H-naphto[1,2-d:4,5-c'd]dipyrano-4,8-dione. Naphthodipyranodione was assumed to be formed by the degradation of gentiopicroside by enzymatic hydrolysis at low water concentration. The degradation pathway was a unique domino-reaction triggered by enzymatic hydrolysis. Naphthodipyranodione may become an index compound for the drying and/or fermenting procedure of Gentian root.