Merocyclophanes A and B, Antiproliferative Cyclophanes from the Cultured Terrestrial Cyanobacterium Nostoc sp.
journal contributionposted on 08.11.2013, 00:00 by Hahk-Soo Kang, Bernard D. Santarsiero, Hyunjung Kim, Aleksej Krunic, Qi Shen, Steven M. Swanson, Hee-Byung Chai, A. Douglas Kinghorn, Jimmy Orjala
The cell extract of a cultured terrestrial Nostoc sp. (UIC 10062), obtained from a sample collected at Grand Mere State park in Michigan, displayed antiproliferative activity against the HT-29 human colon cancer cell line. Bioactivity-guided fractionation of the cell extract, combined with LC-MS analysis, led to the isolation of two new cyclophanes, named merocyclophanes A and B (1 and 2). The planar structures were determined by various spectroscopic techniques including HRESIMS, and 1D and 2D NMR experiments. The stereoconfiguration was assigned on the basis of X-ray crystallographic and CD analyses. The structures of merocyclophanes A and B (1 and 2) revealed a new natural [7.7]paracyclophane skeleton characterized by α-branched methyls at C-1/14. Merocyclophanes A and B (1 and 2) displayed antiproliferative activity against the HT-29 human colon cancer cell line with IC50 values of 3.3 and 1.7 μM, respectively.