# Anti-Inflammatory Butenolides from a Marine-Derived _Streptomyces_ sp. 13G036
## 3 Results
### Structure Elucidation of the Isolated Compounds  
Compound **1** was isolated as yellowish colored oil and its molecular formula was deduced as C\({}_{13}\)H\({}_{20}\)O\({}_{4}\) on the basis of HR-FAB-MS [M + H]\({}^{+}\) 241.1440 (Figure S8 in the Supplementary Materials), indicating four unsaturation numbers. Analysis of \({}^{1}\)H NMR spectrum showed two olefinic signals at \(\delta_{\rm H}\) 7.42 (CH-3) and \(\delta_{\rm H}\) 6.10 (CH-2), one heteroatomic bond CH at \(\delta_{\rm H}\) 5.02 and two singlet methyls at \(\delta_{\rm H}\) 2.21 and \(\delta_{\rm H}\) 1.36.  
Interpretation of the \({}^{13}\)C NMR spectrum of compound **1** showed one ketone (C-11, \(\delta_{\rm C}\) 212.21), one ester carbonyl (C-1, \(\delta_{\rm C}\) 173.05), one olefinic (C-2, \(\delta_{\rm C}\) 121.85; C-3, \(\delta_{\rm C}\) 156.12), two oxygen bonded carbons (C-4, \(\delta_{\rm C}\) 83.35; C-10, \(\delta_{\rm C}\) 78.89) and seven alkyl groups (C-5, \(\delta_{\rm C}\) 33.21; C-6, \(\delta_{\rm C}\) 25.59; C-7, \(\delta_{\rm C}\) 29.57; C-8, \(\delta_{\rm C}\) 23.72; C-9, \(\delta_{\rm C}\) 39.39; C-12, \(\delta_{\rm C}\) 23.29; C-13,\(\delta_{\rm C}\) 24.97). Combined analysis of \({}^{1}\)H and \({}^{13}\)C NMR data suggested that compound **1** could be a butenolide, which is a family of \(\alpha\), \(\beta\)-unsaturated lactones [16; 17].  
The following COSY correlations were observed: \(\delta_{\rm H}\) 6.10 (C-2, CH)/\(\delta_{\rm H}\) 7.42 (C-3, CH), \(\delta_{\rm H}\) 7.42 (C-3, CH)/\(\delta_{\rm H}\) 5.02 (C-4, CH) and \(\delta_{\rm H}\) 5.02 (C-4, CH)/\(\delta_{\rm H}\) 1.68 (C-5, CH)\({}_{2}\)). HMBC correlations (H-13/C-9, C-10, C-11; H-12/C-11; C-10-OH/C-9, C-11, C-13) were also observed as shown in Figure 3. The planar structure of compound **1** was confirmed as (4S)-4,10-dihydroxy-10-methyl-11-oxo-dodec-2-en-1,4-olide (mycenolide A) by comparing the NMR data with published data from the literature [22].  
Likewise, the planar structures of compounds **2**-7 were deduced by comparison of the NMR spectroscopic data with the published data from the literature. The absolute configuration of the C-4 in compounds **1**-7 was assigned by ECD absorption around 210 nm corresponding to positive \(\pi\)-\(\pi\) * Cotton effect (Figure 4) [18].  
The chiral centers at C-10/C-11 in compounds **4** and **7** were confirmed as 10R/115 and 10S/115 by the comparison of the NMR data and specific rotations with the previously reported data of synthetic butenolides [18; 20]. The relative configuration at C-10/C-11 in compound **6** was elucidated as a three (10S *, 11S *) by comparison with the partial  
Figure 3: Key COSY and HMBC correlations of compound **1**.  
Figure 2: The molecular networking map of the fractions A–I. (**A**) A molecular networking map. (**B**) Expansion of the MF-1 cluster.  
structure according to the reported data; however, the absolute configuration has not yet been determined [23; 24].  
Thus, the structures of compounds **1-7** were confirmed as follows: 1, (45)-4,10-dihydroxy-10-methyl-11-oxo-dodec-2-en-1,4-olide; 2, (45)-4,10-dihydroxy-10 -methyl-undec-2-en-1,4-olide [25]; 3, (45)-4,10-dihydroxy-10-methyl-dodec-2-en-1,4-olide [25]; 4, (45,10R,115)-4,11-dihydroxy-10-methyl-dodec-2-en-1,4-olide; 5, (45)-4-hydroxy-10-methyl-11-oxo-dodec-2-en-1,4-olide [20]; 6, (45,105,115)-4,10,11-trihydroxy-10-methyl-dodec-2-en-1,4-olide [25]; 7, (45,105,115)-4,11-dihydroxy-10-methyl-dodec-2-en-1,4-olide. Due to the limitation of compound supply or inactiveness of the stereogenic carbonyls of compounds **1**, **3** and **6**, the absolute configuration of stereogenic centers, except for C-4, could not be determined.