L-755,805, a new polyketide endothelin binding inhibitor from an actinomycete

L-755,805, 1, a hexacyclic polyketide with a novel ring system, has been isolated from an actinomycete culture, MA7150. The planar structure was determined from interpretation of spectroscopic data. 1 inhibits 125I-endothelin binding to ET-A and ET-B receptors with IC50's of 11 and 3.9 μM.