Abstract: New compounds, which we have named the "Leustroducsins" have the formula (I): ##STR1## in which R represents a 5-methylhexanoyloxy group, a 6-methyloctanoyloxy group or a 7-methyloctanoyloxy group, and salts thereof, and may be prepared by fermentation using a microorganism of the genus Streptomyces, especially a strain of the species Streptomyces platensis, such as strain SANK 60191 (FERM BP-3288). These compounds may be used for the treatment or prophylaxis of: adverse reactions resulting from cancer chemotherapy or radiotherapy; infections; cancer; cerebral dysfunction; and fungal infections.