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BACKGROUND Chemically defined media (CDM) are used routinely in industrial settings for the production of biopharmaceuticals from mammalian cells, so attention has shifted to understanding their chemical behavior and impact on process robustness. In this context, one particular problem is the risk of cross reactivity and instability in complex mixtures of chemicals at high concentrations. RESULTS: In order to characterize potentially unstable medium compounds in feed media, we developed and validated a novel liquid chromatography tandem mass spectrometry (LC‐MS/MS) method to simultaneously quantify the majority of medium compounds. We used this application advantage to provide the following insights into molecular processes occurring in CDM prepared at different temperatures and during storage: Concentration profiles of critical compounds in CDM are independent of preparation temperature and storage material but show significant alterations over time. In particular l‐cysteine, l‐proline, vitamin B6, thiamine and cyanocobalamin were found to be rather unstable. Using mixed mode chromatography allows expansion of the method to cover additional analytes of interest, as demonstrated by inclusion of seven additional CDM reaction products. CONCLUSION: The successful development of a new LC‐MS/MS method allowed us to show the impact of storage duration on the stability of CDM compounds. Furthermore, the results suggest that essential parameters for medium preparation (e.g. temperature) and storage upscaling (e.g. vessel material) are not impacting upon the chemical composition of CDM. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Research on ribosomally synthesized and posttranslationally modified peptides (RiPPs) has led to an increasing understanding of biosynthetic mechanisms, mostly drawn from bacterial examples. In contrast, reports on RiPPs from fungal producers, apart from the amanitins and phalloidins, are still scarce. The fungal cyclopeptide omphalotin A carries multiple N-methylations on the peptide backbone, a modification previously known only from nonribosomal peptides. Mining the genome of the omphalotin-producing fungus for a precursor peptide led to the identification of two biosynthesis genes, one encoding a methyltransferase OphMA that catalyzes the automethylation of its C-terminus, which is then released and cyclized by the protease OphP. Our findings suggest a novel biosynthesis mechanism for a RiPP in which a modifying enzyme bears its own precursor peptide., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)