ABSTRACT
Twelve N-terminal analogs of des-fatty acyl-polymyxin B (Des-FA-[X(1)]-PMB, X=various amino acids or peptides) were synthesized and examined for their antimicrobial activity against Escherichia coli (E. coli), Salmonella Typhimurium (S. Typhimurium) and Pseudomonas aeruginosa (P. aeruginosa). It was found that Des-FA-[Dap(1)]-, Des-FA-[Ser(1)]-, Des-FA-[Dab-Dab-Dab(1)]- and Des-FA-[Arg-Arg-Arg(1)]-PMB had potent activity only against P. aeruginosa, with MIC values of 0.5-1 nmol/ml. Analogs in which X was Lys, Arg, Leu or Ala did not have increased antimicrobial activity against the three bacterial species tested compared with the lead compounds Des-FA-[Dab(1)]-PMB and polymyxin B (PMB). Des-FA-[Trp(1)]-PMB and Des-FA-[Phe(1)]-PMB had reduced activity against P. aeruginosa. The results indicate that compact hydrophilic amino acids (C3) or basic tripeptides at the N-terminal provide specificity for bactericidal activity towards P. aeruginosa. For LPS-binding activity, Des-FA-[Dab-Dab-Dab(1)]-PMB and Des-FA-[Arg-Arg-Arg(1)]-PMB showed activity comparable to PMB, while Des-FA-[Ala-Ala-Ala(1)]-PMB showed very low activity. Reduced acute toxicity of Des-FA-[Dap(1)]-PMB and Des-FA-[Trp(1)]-PMB was demonstrated by a mouse tail intravenous administration test, with LD(50) values of 23.5 and 19.0 micromol/kg, respectively, in contrast to PMB (LD(50), 4.8 micromol/kg).
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Oligopeptides/chemical synthesis , Polymyxin B/analogs & derivatives , Pseudomonas aeruginosa/drug effects , Animals , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , Anti-Bacterial Agents/toxicity , Chromatography, High Pressure Liquid , Lethal Dose 50 , Male , Mice , Mice, Inbred Strains , Microbial Sensitivity Tests , Oligopeptides/chemistry , Oligopeptides/pharmacology , Oligopeptides/toxicity , Polymyxin B/chemical synthesis , Polymyxin B/chemistry , Polymyxin B/pharmacology , Polymyxin B/toxicityABSTRACT
Improved strategies for the chemical conversion of natural polymyxin B and colistin to their N-terminal analogs are reported. First, the protection of the side chains of five L-alpha,gamma-diaminobutyric acid (Dab) residues in natural polymyxin B and colistin was achieved with trichloroethoxycarbonyl (Troc), then the resulting pentakis(N gamma-Troc)-polymyxin B and pentakis(N gamma)Troc)-colistin were treated with trifluoroacetic acid (TFA) : methanesulfonic acid (MSA) : dimethylformamide (DMF) : H2O (10 : 30 : 55 : 5) at 40 degrees C in order to remove N alpha-alkanoyl-Dab(Troc)-OH selectively. The new key compounds, tetrakis(N gamma-Troc)-polymyxin B (2-10) and tetrakis(N gamma-Troc)-colistin (2-10), were obtained in 19% and 15% yields, respectively, which is higher than previous reports using trifluoroacetyl (Tfa) for tetrakis(N gamma-Tfa)-polymyxin B (2-10) and tetrakis(N gamma-Tfa)-colistin (2-10), respectively. Acylation of tetrakis(N gamma-Troc)-polymyxin B (2-10) and tetrakis(N gamma-Troc)-colistin (2-10) with various hydrophobic acids bearing aliphatic or aromatic ring structures, followed by the deprotection of Troc by Zn in AcOH, produced polymyxin B (2-10) and colistin (2-10) analogs which were used for structure-activity relationship studies. It was found that cyclohexylbutanoyl-, 4-biphenylacetyl-, and 1-adamantaneacetyl-polymyxin B (2-10) showed potent antimicrobial activity equal to that of polymyxin B against three Gram-negative bacterial strains. The lipopolysacharide (LPS) binding activity of cyclohexylbutanoyl-, 4-biphenylacetyl-, and cyclododecanecarbonyl-polymyxin B (2-10) increased greatly in comparison with that of polymyxin B (2-10). The various N alpha-acylated polymyxin B (2-10) analogs showed slightly higher antimicrobial and LPS binding activities than the corresponding N alpha-acylated colistin (2-10) analogs.
