By utilizing a bioassay-guided separation (P388 lymphocytic leukemia and a panel of human cancer cell lines) offermentation broths from a
Kitasatospora sp. collected from a tundra soil sample taken at the shore of the Beaufort Sea,we have isolated three powerful (GI
50 to 0.0006
![](/images/entities/mgr.gif)
g/mL) cancer cell growth inhibitors (
1-
3) and determined their structuresto be closely related cyclodepsipeptides. From 380 L fermentations of
Kitasatospora sp. were obtained 2.6 mg of a newcyclodepsipeptide designated kitastatin 1 (
3), accompanied by the previously known respirantin (
1, 10.8 mg) and itsvaleryl homologue (
2, 4.8 mg). The structures were determined by employment of a series of high-resolution mass and2D NMR spectroscopic analyses. The stereochemical assignments and overall structures were confirmed by subsequenttotal synthesis of depsipeptide
1, as reported in the accompanying contribution.