## 2 Results
### Structural Elucidation of Compounds **1** and **2**  
The mutant M6 was selected to perform large-scale liquid fermentations under the same conditions as the small-scale fermentation. Total liquid cultures of M6 were extracted with organic solvent. Two novel benzopyran compounds **1** and **2**, as well as xiamenomycin (Figure 2), were isolated from peak F (Figure 1) after semi-preparative HPLC purification. The retention times of **1** and **2** are quite close to that of xiamenomycin during the HPLC analysis; thus, it was difficult to detect these two compounds from the crude extract initially. The molecular formula of **1** was determined to be C\({}_{17}\)H\({}_{23}\)NO\({}_{3}\) by HRESIMS (\(m\)/\(z\) = 290.1768 \(\left[\mathrm{M}+\mathrm{H}\right]^{+}\), positive ion mode and \(m\)/\(z\) = 288.1610 \(\left[\mathrm{M}-\mathrm{H}\right]^{-}\), negative ion mode). Based on similar UV characteristics, compound **1** was considered to be a derivative of xiamenomycin. The \({}^{1}\)H and \({}^{13}\)C NMR data, in combination with the HMBC and the HMQC correlations, resulted in the identification of benzopyran as the main structural feature. The HMBC correlations between H\({}_{2}\)-9 (\(\delta_{\mathrm{H}}\) 1.59, m), C-2 (\(\delta_{\mathrm{C}}\) 79.7), and C-3 (\(\delta_{\mathrm{C}}\) 66.3) confirmed the isoprenyl side chain to be located at C-2. The substituent position of the carboxamide was determined to be C-6 in the benzopyran skeleton based on the HMBC correlation between H-5 (\(\delta_{\mathrm{H}}\) 7.63, d, 1.8), H-6 (\(\delta_{\mathrm{H}}\) 7.60, dd, 8.4, 1.8) and C-1' (\(\delta_{\mathrm{C}}\) 168). The main difference in the NMR data between **1** and xiamenomycin was found in the amino acid moieties and was due to the missing signal related to the 1'-6' positions in the \({}^{1}\)H and the \({}^{13}\)C NMR spectra (Table 2). From biosynthetic reasoning and the similarity of the CD data compared with xiamenomycin, we assumed that compound **1** has the identical absolute configuration as xiamenomycin in the benzopyran portion of the molecule. Accordingly, the structure of **1** was identified as (25,35)-3-hydroxy-2-methyl-2-(4-methylpent-3-enyl)chroman-6-carboxylate and was named xiamenomycin C.  
Compound **2** gave a _pseudo_-molecular ions \(\left[\mathrm{M}+\mathrm{H}\right]^{+}\) peak at \(m\)/\(z\) = 406.2210 by HRESIMS, consistent with an elemental composition of C\({}_{22}\)H\({}_{31}\)NO\({}_{6}\), which was 15 amu more than the molecular weight of xiamenomycin. The \({}^{1}\)H and \({}^{13}\)C NMR data showed an additional methyl group due to the presence of signals at \(\delta_{\mathrm{H}}\) 3.65 (3H, s) and \(\delta_{\mathrm{C}}\) 52.3 (CH\({}_{3}\)). The HMBC correlations between CH\({}_{3}\)-7' and CO-6' (\(\delta_{\mathrm{C}}\) 171.8) confirmed the methyl esterification. The good agreement of the respective NMR data of **2** with those of xiamenomycin, together with ROESY data and proton coupling constants indicated that both compounds shared the same relative configurations of pyran-ring and the amino acid portion. Compound **2** possessed the same stereo-configurations as xiamenomycin, confirmed by the similar CD  
Figure 2: Structures of the anti-fibrotic benzopyran compounds **1**, **2**, and xiamenomycin. spectrum. Therefore, the structure of **2** was determined as (2\(R\),3_S_)-methyl 3-hydroxy-2-((2\(S\),3_S_)-3-hydroxy-2-methyl-2-(4-methylpent-3-enyl)chroman-6-carboxamido)butanoate, named xiamenomycin D.  
Inhibition of the Proliferation of Human Diploid Lung Fibroblast (WI26) Cells by Compounds **1** and **2**  
Fibroblasts play pivotal roles in establishing and maintaining the self-perpetuating inflammatory circuits and are, in fact, the main ECM generating cells in fibrotic diseases [18]. Thus, finding a small molecule that can slow the rapid fibrotic response would be a reasonable way to develop an anti-fibrotic drug. We investigated the anti-proliferative activities of **1** and **2** against human lung fibroblast.