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Abstract MS/MS-based molecular networking is an effective strategy to rapidly dereplicate known compounds and to guide the discovery process for new and novel natural products. In the present study, the chemical diversity of indole diterpenoids from the marine-derived fungus Penicillium sp. N4-3 was investigated using molecular networking techniques. Guided by this information, targeted isolation resulted in two new indole diterpenoids shearinines R and S ( 1 , 2 ) and an oxidative artifact shearinine T ( 3 ), together with the verification of two known analogs ( 4 , 5 ). Furthermore, five indole diterpenoids ( 6 − 10 ), including three putatively new ones, shearinines U−W ( 6 , 9 , 10 ), were predicted from the molecular ion cluster by the combination of GNPS molecular networking and manual analysis of MS/MS fragmentation clusters. Shearinines T ( 3 ) and W ( 10 ) are characterized by an oxidative cleavage of the C-2–C-18 double bond. Feature fragment ions of these shearinines revealed two type of dominant ions related to the indole moiety and the breaking of C-9 side chain or Ring I. Compound 1 showed antibacterial activities against a panel of pathogenic bacteria with IC 50 values ranging from 6.34 to 47.96 μg/mL and inhibited the growth of the human hepatic (HepG2) and gastric (SGC-7901) cancer cells lines with IC 50 values of 6.27 and 19.16 μg/mL, respectively.
Chen et al. (Mon,) studied this question.