142563-39-1 A2bu-Cyclo(A2bu-A2bu-phe-leu-A2bu-A2bu-thr) Dab-cyclo(dab-dab-phe-leu-dab-dab-thr) sulfate salt Diaminobutyryl-cyclo(diaminobutyryl-diaminobutyryl-phenylalanyl-leucyl-diaminobutyryl-diaminobutyryl-threonyl) PBOP Polymyxin B octapeptide