Three new unstable metabolites, (6 E,10 Z)-2′- O-methylmyxalamide D ( 1 ), 2′- O-methylmyxalamide D ( 2 ) and (6 E)-2′- O-methylmyxalamide D ( 3 ) were isolated from the myxobacterium Cystobacter fuscus. The planar structures were elucidated by spectroscopic analyses to be geometrical isomers of a polyene amide related to a myxobacterial metabolite, myxalamide D ( 4 ). Their absolute stereochemistry was determined by synthesis of degradation products. Antifungal activities of 1– 3 as well as their acetates were evaluated against the phythopathogenic fungus Phythopthora capsici.