The full structure of colistin B was determined as IOA→(α) DAB→-Thr→(α) DAB→(α) cyclo-(γ) DAB→(α) DAB→D-Leu→(α) DAB→(α) DAB→-Thr→with combination of enzymatic digestion and acid partial hydrolysis. The structure is identical to that of colistin A, with the exception that colistin B contains isoöctanoic acid instead of 6-methyl-octanoic acid in colistin A.
The authors with to thank Mr. T. Yano of Banyu Pharmaceutial Co., Ltd. for a gift of commercial colistin and to express our appreciation to Dr. T. Kawano of Osaka College of Pharmacy for the microbiological analysis.