The present invention relates to novel compounds, termed serpentemycins, of the formula (I) ##STR00001## in which Y, R, R.sub.2, R.sub.3, R.sub.4, X, X.sub.2, X.sub.3, n, m and o are as defined in the specification, which are formed by the microorganism Actinomycetales sp. DSM 14865 during its fermentation, to chemical derivatives of the serpentemycins, to a process for preparing them, and to their use as pharmaceuticals, in particular for the treatment and prophylaxis of infectious bacterial diseases.