# Naphthoquinone-Based Meroterpenoids from Marine-Derived _Streptomyces_ sp. B9173
## 3 Results
### Structural Elucidation of Naphthoquinone Family Metabolites
The 1D NMR data of **2** were similar to those of **1**, but there were ten more carbon signals including four double-bond carbons (\(\delta_{C}\): 119.8 (d); 142.6 (s); 123.7 (d); 131.8 (s)), three CH\({}_{2}\) (\(\delta_{C}\): 69.8 (t); 39.6 (t); 26.3 (t)), and three CH\({}_{3}\) (\(\delta_{C}\): 25.6 (q); 16.5 (q); 17.6 (q)), indicating that **2** contains a geranyl group. A dimethylallyl group in **2** was constructed by HMBC from two allylic methyls (\(\delta_{H}\) 1.65, H-8\({}^{\prime}\); \(\delta_{H}\) 1.58, H-10\({}^{\prime}\)) to \(\delta_{C}\) 131.8, C-7\({}^{\prime}\) and \(\delta_{C}\) 123.7, C-6\({}^{\prime}\) and a COSY cross-peak between \(\delta_{H}\) 5.05, H-6\({}^{\prime}\) and \(\delta_{H}\) 2.03, H-5\({}^{\prime}\). Another isoprene unit was identified by HMBCs from \(\delta_{H}\) 1.70 (s, CH\({}_{3}\), H-9\({}^{\prime}\)) and \(\delta_{H}\) 2.06 (m, CH\({}_{2}\), H-4\({}^{\prime}\)) to \(\delta_{C}\) 142.6 (C-3\({}^{\prime}\)) and \(\delta_{C}\) 119.8 (C-2\({}^{\prime}\)) and a vicinal coupling between \(\delta_{H}\) 5.49 (m, CH, H-2\({}^{\prime}\)) and \(\delta_{H}\) 4.87 (d, 2H, H-1\({}^{\prime}\)). The two units were joined between \(\delta_{H}\)  
Figure 3: \({}^{1}\)H-\({}^{1}\)H COSY (bold lines) and HMBC correlation (arrows) supporting planar structures of **1**-**3**. 2.06 (H-4\({}^{\prime}\)) and \(\delta_{H}\) 2.03 (H-5\({}^{\prime}\)) through COSY spectrum analysis. A geranyl group thus obtained was connected to 2-O from the correlation between \(\delta_{H}\) 4.87 (H-1\({}^{\prime}\)) and \(\delta_{C}\) 158.7 (C-2). Thus, **2** was established as (_E_)-8-amino-3-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-8-hydroxy-6-methoxy-2-methylnaphthalene-1,4-dione (Figure 3, Figure S4 and Table 2). Flaviogeranin D (**3**) was obtained as orange oil. [\(\alpha\)]\({}^{23}_{\rm D}\) +16.3 (c 0.10, CH\({}_{3}\)Cl); UV (CH\({}_{3}\)Cl) \(\lambda_{\rm max}\) (log \(\varepsilon\)): 256 (3.90), 310 (3.46), 353 (3.34) nm; HRESIMS analysis afforded an [M + H]\({}^{+}\) ion at \(n\)/z 359.1839, giving the molecular formula of **3** as C\({}_{21}\)H\({}_{26}\)O\({}_{5}\) (calcd. 359.1824 for [M + H]\({}^{+}\)). The \({}^{13}\)C and DEPT NMR spectra of **3** suggested the presence of four methyl (\(\delta_{C}\) 8.1, C-9; \(\delta_{C}\) 16.1, C-9\({}^{\prime}\); \(\delta_{C}\) 25.6, C-8\({}^{\prime}\); \(\delta_{C}\) 17.6, C-10\({}^{\prime}\)), one oxygenated quaternary carbon (\(\delta_{C}\) 77.9, C-2), four CH\({}_{2}\) (\(\delta_{C}\) 49.1, C-3; \(\delta_{C}\) 38.9, C-1\({}^{\prime}\); \(\delta_{C}\) 39.8, C-4\({}^{\prime}\); \(\delta_{C}\) 26.3, C-5\({}^{\prime}\)), two carbonyls (\(\delta_{C}\) 199.7, C-1; \(\delta_{C}\) 198.9, C-4), three olefin CH (\(\delta_{C}\) 116.0, C-2\({}^{\prime}\); \(\delta_{C}\) 123.9, C-6\({}^{\prime}\); \(\delta_{C}\) 106.5, C-8), and seven nonprotonated double-bond carbons (\(\delta_{C}\) 112.0, C-4a; \(\delta_{C}\) 161.2, C-5; \(\delta_{C}\) 119.2, C-6; \(\delta_{C}\) 162.1, C-7; \(\delta_{C}\) 131.4, C-8a; \(\delta_{C}\) 141.0, C-3\({}^{\prime}\); \(\delta_{C}\) 123.9, C-6\({}^{\prime}\)). A reduced naphthalene-1,4-dione substructure was constructed through analysis of the HMBC correlation from \(\delta_{H}\) 7.07 (H-8) to \(\delta_{C}\) 119.2 (C-6), \(\delta_{C}\) 112.0 (C-4a) and \(\delta_{C}\) 199.7 (C-1); \(\delta_{H}\) 2.19 (H-9) to \(\delta_{C}\) 119.2 (C-6), \(\delta_{C}\) 162.1 (C-7) and \(\delta_{C}\) 161.2 (C-5); \(\delta_{H}\) 3.23 and 3.13 (d, \(J\) = 16.8 Hz, H-3) to \(\delta_{C}\) 198.9 (C-4), \(\delta_{C}\) 112.0 (C-4a), and \(\delta_{C}\) 199.7 (C-1). A geranyl group was identified in comparison with the NMR data of **2** and connected to C-2 (\(\delta_{C}\) 77.9) based on the correlation from \(\delta_{H}\) 4.98 (C-2\({}^{\prime}\)) to \(\delta_{C}\) 77.9 (C-2); \(\delta_{H}\) 2.49, 2.38 (H-1\({}^{\prime}\)) to \(\delta_{C}\) 199.7 (C-1), \(\delta_{C}\) 77.9 (C-2), and 39.1 (C-3).