The invention relates to novel polyenes having formula (I), wherein: R1 represents alkyl, C1-C3; and R2 represents a functional group selected from CH3- or CONH2- (methyl or primary amide). The aforementioned polyenes have a biocide action on organisms comprising cell membranes that contain ergosterol, e.g. fungi or parasites. Said compounds can be obtained using a method that consists in cultivating a producing micro-organism under conditions that enable the production thereof. In addition, the invention also relates to a mechanism for the in vitro production of amidated polyenes, consisting in incubating carboxylated polyenes with cell-free extracts (or proteinaceous fractions) of the producers of same in the presence of ATP/Mg++ and an amide-group donor compound (preferably glutamine).