The 18 Da increase in mass was Selleckchem OICR-9429 attributed to the hydrolysis of a lactone. This result indicated that the two compounds were cyclic lipopeptide antibiotics. The MS/MS spectrum
of the doubly charged precursor ion of the hydrolyzed compound at m/z 567.4 with a mass of 1133 Da was shown in Figure 1. Successive fragmentations from the two termini of the ring-opened lipopeptide resulted in b-type ions at m/z 1014.3, 901.2, 802.1, 702.1, 589.1, 441.9, 341.9, and 228.8, along with corresponding y-type ions detected at m/z 905.2, 792.1, 692.0, 544.9, 431.9, 331.6, and 232.7. These fragment ions allowed for the assignment of the following sequence: Ile/Leu-Dab-Phe- Leu/Ile-Dab-Val-Leu/Temsirolimus clinical trial Ile-Thr-OH. The b-type ions at m/z 228.8 corresponded to fatty acid (FA)-Dab, which indicated that the fatty acyl moiety has the elemental composition of C7H12O2. Figure 1 MS/MS spectrum of PE1 and its proposed amino acid sequence. (A) MS/MS spectrum of the doubly charged precursor ion at m/z 567.4 of the
hydrolyzed PE1 of 1,133 Da. (B) Proposed amino acid sequence of PE1. The ring-opened PE2 with a mass [M + H]+ of 1,119 Da was also analyzed by CID. The tandem mass spectrum of this this website derivative was shown in Figure 2. All of the b-type ions that were generated from this doubly charged precursor ion [M + 2H]2+ at m/z 560.3 were 14 Da less than those generated from the precursor ion [M + 2H]2+ at m/z 567.4. However, the two y-type ion series for the two compounds were almost the same in mass, which indicated that the two compounds had identical amino acid sequences but different fatty acid chains. Similar to PE1, PE2 also produced a fragment ion at m/z 905.1, which corresponded
to the loss of 214 Da from the [M + H]+ ion. Examination of the neutral fragment that was lost suggested that it contains a Dab residue and a fatty acyl moiety (C6H10O2). These results further confirmed that the two compounds were different in their fatty acyl moieties. Figure 2 MS/MS spectrum of PE2 and its proposed amino acid sequence. (A) MS/MS spectrum of the doubly charged precursor ion at m/z 560.3 of the hydrolyzed PE2 of 1,119 Da. (B) Proposed amino acid sequence of PE2. Apart from in the C-terminal amino acid (Thr), no hydroxyl group was found in the peptide moieties of P. ehimensis lipopeptides studied here. Thus, a lactone linkage was Thiamet G only formed between the carboxyl group of the C-terminal and the hydroxyl group of fatty acid moieties. The proposed structures for PE1 and PE2 are showed in Figure 3. Figure 3 Proposed structures of PE1 and PE2 produced by Paenibacillus ehimensis B7. Antimicrobial activities of the purified compounds The antimicrobial activities of the purified compounds PE1 and PE2 were measured using micro dilution methods. Table 1 showed that PE1 and PE2 both had a similar level of strong activity against all of the tested Gram-positive and Gram-negative pathogens as well as Candida albicans.