Analysis of the NMR (DMSO-d6) data for symphyocladins J/K (9a/b) (Figures S30 and S31, Table 1, Table 2 and Table S8) identified an inseparable mixture of C-6 CO2Me homologues of 7a/b and 8a/b, as evidenced by spectroscopic comparisons and diagnostic HMBC correlations from the additional CO2Me resonances to C-6 (Figure 3). In this instance, as hydrogen bonding does not stabilize double bond isomers, the Z/E mixture prevails even in an aprotic solvent (i.e., DMSO-d6). Analysis of the NMR (acetone-d6) data for symphyocladin L (10) (Figures S32 and S33, Table 3, Table 5 and Table S9) revealed a ∆3,4 isomer and 1-CO2Me homologue of 7a/b and 8a/b, as evidenced by COSY correlations between H-2 and H2-7′, and diagnostic HMBC correlations positioning both C-1 CO2Me and C-5 CO2Me (Figure 3). The structure of 10 inclusive of an E ∆3,4 configuration and its racemic nature were confirmed by single crystal X-ray analysis with the compound crystallizing in a centrosymmetric space group (Figures S34 and S35). Analysis of the NMR (methanol-d4) data for symphyocladin M (11) (Figures S36 and S37, Table 3, Table 5 and Table S10) revealed it as a C-6 CO2Et homologue of 10, as evidenced by spectroscopic comparisons and an HMBC correlation from the CO2Et moiety to C-6.