Unraveling Structures Containing Highly Conjugated Pyrrolo[4,3,2-de]quinoline Cores That Are Deficient in Diagnostic Proton NMR Signals

This study began with the goal of identifying additional constituents from Zyzzya fuliginosa extracts obtained from an Indo-Pacific sponge (coll. no. 06132). The previous work identified several red and green pyrroloiminiquinones (aka pyrrolo­[4,3,2-de]­quinolines), and this reinvestigation provided two additional analogues, a blue compound named zyzzamine A (1) and a green compound named zyzzamine B (2). The relatively low ratio of H/[sum­(CNO)] = 0.71 or 0.76 of this pair greatly complicated the final steps of compound characterization and required the use of five 2D NMR strategies and MS² data sets.