A new natural Pepstatin from Kitasatospora (Actinomycetales)
The pepstatins are linear peptides biosynthesized and excreted into culture filtrates by several species of Actinomycetes and are well known inhibitors of aspartic proteinases, such as pepsin and cathepsins D and E. Apart from their role as proteinase inhibitors, their other pharmacological and cellular activities remain unclear.
Our lab has isolated Pepstatin A  and a new member of this family from an actinomycete strain belonging to the genus Kitasatospora. BLAST searches and sequence alignments of partial ribosomal DNA sequences revealed that this strain is closely related to strains of the species Kitasatospora mediocidica. The producing organism was isolated from the rhizosphere of a juniper-tree (Juniperus communis L.) after plating and incubation of a soil suspension on a selective glycerol arginine agar isolation medium. How was it fermented? Fermentation discovery strategy?
A 1L fermentation of the strain was extracted with acetone and, after evaporation of the organic solvent, fractionated on a SPE resin (SP207ss) on reverse phase mode. Acetonitrile/water semi-preparative HPLC gradient of one of these fractions led us to the detection (LC/MS) of two components related to the pepstatin family. Both secondary metabolites were isolated by preparative HPLC under similar conditions. Structural elucidation of both components was based on NMR (1H, 13C, COSY, HSQC, HMBC) and low and high resolution Mass Spectrometry (LC/MS-ESI) data. The isolated compounds were finally identified as pepstatin A and the new derivative we designate as pepstatin K. Data on the isolation, structural characterization and biological properties of both compounds will be presented.
References: . Umezawa H et al. (1970)J Antibiot 23: 259