MS-681a, b, c and d, new inhibitors of myosin light chain kinase from Myrothecium sp. II. Physico-chemical properties and structure elucidation.

MS-681a, b, c and d are new inhibitors of myosin light chain kinase produced by Myrothecium sp. They are novel octapeptides containing alpha-alkyl-alpha-amino acids and a polyamine moiety. The structures were determined by NMR and FAB-MS/MS spectral analyses of the intact peptides. Their absolute configurations were elucidated by GC analysis on a chiral column of the constituent amino acids and by chemical synthesis of the polyamine moieties.