# Anti-Inflammatory Butenolides from a Marine-Derived _Streptomyces_ sp. 13G036
## 1 Introduction  
Acute and chronic inflammation is a complex biological response of the body to various external stimuli including pathogens, damaged cells and toxins, resulting in various diseases, such as allergies, inflammatory bowel diseases, sepsis, cancer and Alzheimer's disease [1, 2, 3]. Many studies have reported several signaling pathways that are associated with the initiation and progression of inflammation in canonical/non-canonical fashions and that are essential factors for successful therapy of inflammation-related diseases [4].  
Even though many attempts have been made to discover potent anti-inflammatory agents in small molecule drugs or natural compounds, the therapeutic outcomes are still not satisfactory owing to limitations and potential risks. Thus, the development of new anti-inflammatory agents without adverse effects is urgently required for clinical application.  
Microbial natural products are regarded as one of the major sources of bioactive compounds and have been used as potential drug leads. Marine-derived actinobacteria is the most prolific group of microorganisms that provide bioactive natural products [5, 6, 7]. Particularly, cyclomavirus and salinamides have been reported as marine actinobacteria-derived anti-inflammatory natural products [8, 9].  
The increasing rediscovery rate of natural products and a time-consuming dereplication process have become bottlenecks that retard the progress of natural product-derived drug discovery. With the advent of new techniques, there are commonly used natural product databases, such as \"MarineLit\", \"Antibase\" and the \"Dictionary of Natural Products\", which relay the MS information of samples to dereplicate known natural products [10; 11; 12]. These databases, however, cannot enable automatic spectral mining of large experiments with up to thousands of samples within few hours [13].  
The tandem mass spectrometry (MS/MS)-based dereplication platform, called 'Global Natural Products Social Molecular Networking (GNPS)', is widely used today to shorten the dereplication time and investigate the molecular groups in the mixture samples, such as crude extracts and fractions [13; 14; 15; 16; 17]. GNPS provides the molecular annotation results if the observed MS/MS data of the chemical components in samples are found in the GNPS-database. Although the acquired MS/MS data in this study were not found from the GNPS-database, the GNPS platform provided the molecular networking map showing the molecular families with their associated compound nudes.  
As the part of our goal to discover anti-inflammatory natural products, _Streptomyces_ sp. 13G036 was cultured in SYP broth medium. Molecular networking analysis on the crude extract of _Streptomyces_ sp. 13G036 using the GNPS platform showed several molecular clusters without molecular annotation results. Among the molecular clusters, the Molecular Family-1 (MF-1) cluster was found to consist of molecules mostly possessing parent ion mass values (_m/z_) between 200 and 250 amu. Further LC-ESI-MS analysis on the subfractions of the extract showed that members of the MF-1 cluster were mostly found in the subfractions B-D.  
Further LC-ESI-MS-guided isolation led to the purification of compounds **1-7** possessing butanolide structures (Figure 1). The natural occurrence of compound **7** has not been reported previously. Importantly, compounds **1-6** showed potential anti-inflammatory effects by inhibiting the production of NO, TNF-\(\alpha\) and IL-6 in LPS-stimulated macrophages via down-regulation of NF-\(\kappa\)B (nuclear factor kappa-light-chain-enhancer of activated B cells) activity.