MS-681a, b, c and d, New Inhibitors of Myosin Light Chain Kinase from Myrothecium sp. KY6568. I. Characterization of Producing Strain and Production, Isolation and Biological Activities.

Novel compounds MS-681a, b, c and d were isolated from the culture broth of a fungal strain KY6568. The strain was identified as Myrothecium sp. from its morphological characteristics. MS-681a, b, c and d inhibited the activity of purified smooth muscle myosin light chain kinase with IC50 values of 0.11, 0.29, 0.095 and 0.26 microM, respectively. Cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase and protein kinase C were not inhibited at 100 microM by MS-681 compounds.