Three new unstable metabolites, (6E,10Z)-20 -O-methylmyxalamide D (1), 20 -O-methylmyxalamide D (2) and (6E)-20 -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.