Nucleocidin is a fluorine-containing nucleoside produced by Streptomyces calvus. During 1968 the attempts to identify nucleocidin were made and at that time it was assigned to a structure of a 9-adenyl-4' -sulfamoyloxypentofuranoside, which was mainly based on experiments from pmr and mass spectroscopy, as well as testing in chemical reactions. It was ultimately proven to have a structure of a 4' -fluoro-5' -O-sulphamoyladenosine. Nucleocidin is an antibiotic that can be produced from Streptomyces calvus that grows on Indian land. It is essentially toxic for mammals, although nucleocidin is able to function against bacteria, such as gram negative, and gram positive. Moreover it can be used against trypanosomes.