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

Abstract

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.

Crews' rule—Still useful but often misquoted

“…[1] Some authors, familiar with the contents of the original publication, have applied or quoted this correctly. [2][3][4][5][6][7] Unfortunately, the first easily located publication [8] using the term Crews' rule gives the critical H/C atom ratio as 2 rather than the value of 1 given in the original paper. This error has propagated through the literature [9][10][11][12][13][14][15][16][17][18] and continues to do so to this day.…”

Current Perspectives on Pyrroloiminoquinones: Distribution, Biosynthesis and Drug Discovery Potential

“…They include the secobatzellines from a Caribbean Strongylodesma sp. sponge [19] (reassigned from Batzella [81]); zyzzyanones from Australian Z. fuliginosa [45,82]; makaluvic acids from Micronesian Z. fuliginosa [40] and South African Strongylodesma aliwaliensis [83]; the oxazole-containing makaluvamine W from Tongan Strongylodesma tongaensis [53]; the structurally related citharoxazole from Mediterranean Latrunculia citharistae [84] and zyzzyamines from Papua New Guinean Z. fuliginosa [85].…”

“…They include the secobatzellines from a Caribbean Strongylodesma sp. sponge [19] (reassigned from Batzella [81]); zyzzyanones from Australian Z. fuliginosa [45,82]; makaluvic acids from Micronesian Z. fuliginosa [40] and South African Strongylodesma aliwaliensis [83]; the oxazole-containing makaluvamine W from Tongan Strongylodesma tongaensis [53]; the structurally related citharoxazole from Mediterranean Latrunculia citharistae [84] and zyzzyamines from Papua New Guinean Z. fuliginosa [85]. Pyrroloiminoquinone isolations commonly result in the recovery of ortho-quinone analogs of makaluvamines, named damirones [86] (Figure 4; some analogs are referred to as batzellines [87] and this structural archetype also encompasses makaluvamine O).…”

Transition-metal-free approach to quinolines via direct oxidative cyclocondensation reaction of N,N-dimethyl enaminones with o-aminobenzyl alcohols

“…Quinolines represent an important class of heterocyclic compounds, which widely occur as a core structural motif in natural products ( McCormick et al, 1996 ; Subbaraju et al, 2004 ; McCauley et al, 2020 ), pharmaceuticals ( Gorka et al, 2013 ; Kokatla et al, 2013 ; Jentsch et al, 2018 ), functional materials ( Tong et al, 2003 ; Kim et al, 2005 ; Zhang et al, 2014 ), organocatalysis or ligands ( Biddle et al, 2007 ; Zhang and Sigman., 2007 ; Esteruelas et al, 2016 ), and valuable building blocks ( Wan et al, 2016 ; Duan et al, 2018 ; Wang et al, 2019 ; Ankade et al, 2021 ). Due to their great importance, considerable efforts have been focused on the development of efficient synthetic methods to their structures and modifications over the past years.…”