Myxobacteria are recognized as one of the outstanding prokaryotic sources of bioactive compounds in nature. More than 100 core structures with diverse biological activities had been elucidated, most of which were novel.1 In the continuous screening program for anti-infectives focusing on novel, rare, and unexplored myxobacterial taxa, great potential was discovered in Angiococcus disciformis SBAn001. The strain was routinely cultivated in TS-6 medium (Tryptone (Difco, BD Biosciences, San Jose, CA, USA) 0.6%, MgSO4·7H2O 0.2%, soluble starch (Roth, Karlsruhe, Germany) 0.4%, HEPES 1.19%, pH adjusted to 7.2 with KOH before autoclaving).

HRESI (+)MS analysis of 1 (Table 1) revealed a pseudomolecular ion ([M+Na]+) indicative of a molecular formula (C23H26O4) requiring 11 double bond equivalents. Examination of the NMR (methanol-d4) data (Table 2, Supplementary Figures S1–S4) revealed 15 sp2 carbon resonances, 12 of which were attributed as aromatic (δC 115.3–157.4), an olefinic double bond (δC 105.8, 153.2) and an ester carbonyl (δC 175.1) accounting for 7 double bond equivalent and requiring that 1 be tricyclic. Analysis of the 1D and 2D NMR data revealed equivalent aromatic protons H-2′′ plus H-6′′ (δH 7.00, d, 7.6) and H-3′′ plus H-5′′ (δH 6.63, d, 8.3), which showed HMBC correlations to their same HSQC-correlated 13C resonances, the quaternary carbons C-1′′ (δC 127.5), C-4′′ (δC 157.4) and to the methylene C-6 (δC 41.2), indicating the presence of a 4-hydroxybenzyl moiety (Figure 1). COSY correlations from the aromatic methines H-2′ to H-6′ extended by HMBCs to the olefinic methine H-5 (δH 5.25) led to the construction of a mono-substituted aromatic ring attached to an exocyclic double bond (Figure 1). Moreover, HMBCs from H-2 (δH 2.83) to the ester carbonyl C-1 (δC 175.1) and to an oxy quaternary carbon C-3 (δC 80.8), and from H2-6 (δH 2.96, 2.65) to C-2 (δC 52.2), C-3, and the oxygenated sp2 carbon C-4 (δC 153.2) and together with long-range correlations from H-5 to C-3 and C-4 corraborated the presence of a substituted furanone ring. The final substituent on the furanone ring by examination of the COSY spectra revealed an isolated spin system (H3-11- H-2) consistent with an isopentyl group (Figure 1). On the basis of these data, the planar structure of angiolactone (1) was determined to be 5-benzylidene-4-hydroxy-4-(4-hydroxybenzyl)-3-isopenty-γ-butyrolactone. Despite our efforts in experimenting with different media components to get a better production for 1, we were unsuccessful in ramping up production of 1 and as a result were not able to acquire enough material to address the stereochemistry and bioactivity of 1.

Table 1 Physico-chemical properties of 1
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Table 2 NMR (500 MHz, methanol-d4) data for angiolactone (1)
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