Isolation and structure elucidation of merocyclophane C from the cultured cyanbacterium Nostoc sp. (UIC 10110)

Cyanobacteria are known to be prolific producers of biologically active natural products. Initial screening of the extract of UIC 10110, a Nostoc sp. based on 16S rRNA phylogenetic analysis, found it to be cytotoxic against MDA-MB-435 cells and HT-29 cells in an antiproliferation assay. Dereplication by mass spectrometry and NMR indicated the presence of a potentially novel active constituent which was isolated using semipreparative C18 HPLC. Accurate mass spectrometry allowed for the determination of the molecular formula. This in combination with the proton NMR spectrum revealed the active compound to be a [7,7] paracyclophane. The complete structure of Merocyclophane C was determined by a combination of 1D and 2-D NMR experiments. The absolute stereoconfiguration of Merocyclophane C was determined by CD spectroscopy.