2-Phenylbutyryl colistin nonapeptide hydrochloride 52438-36-5 Polymyxin E1, 1-de(N(sup 2)-(6-methyl-1-oxooctyl)-L-2,4-diaminobutanoic acid)-2-(N-(1-oxo-2-phenylbutyl)-L-threonine)-, hydrochloride