Entrapment of peptidoglycans and adamantyltripeptides into liposomes: an HPLC assay for determination of encapsulation efficiency.

The encapsulation of different immunomodulating peptides, the peptidoglycan monomer, its semisynthetic derivatives (Adamant-1-yl)-acetyl-peptidoglycan monomer and Boc-Tyr-peptidoglycan monomer, respectively, and of two diastereoisomers of adamantyltripeptides into the large negatively charged multilamellar liposomes was investigated. The reproducible quantitative method using HPLC was established for the determination of the entrapped compounds. It was shown that the tested compounds could be efficiently incorporated into liposomes using either the film or modified film method. The results confirmed that the peptidoglycans with lipophilic substituents and particularly the adamantyltripeptides were incorporated into liposomes with higher efficiency than the peptidoglycan monomer using either of the described methods. Liposome preparations were stable at 4 degrees C up to seven days as shown by minimal leaking of the entrapped material.

Modified glycopeptides related to cell wall peptidoglycan: conformational studies by NMR and molecular modelling.

Polymeric peptidoglycans of bacterial cell walls, and smaller glycopeptides derived from them, exhibit versatile biological activities including immunomodulating properties. Peptidoglycan monomer (PGM) was isolated from Brevibacterium divaricatum and novel lipophilic derivatives of PGM bearing either (adamantyl-1-yl)-acetyl or Boc-Tyr substituents (Ad-PGM and BocTyr-PGM respectively) have recently been synthesized. We have obtained full assignments of the 1H and 13C spectra, using 2D NMR techniques, for all three compounds in DMSO solutions. NOESY/ROESY experiments have provided interproton distance restraints that were used in distance geometry modelling calculations to derive conformational preferences for each of these molecules. These data were supplemented with information available from chemical shifts, temperature dependence of amide proton shifts and proton-proton scalar couplings. Analysis of the results suggest that the lipophilic substituents attached to the Dap(3)- epsilon amino group of the parent PGM molecule introduce changes to the conformational preferences of the peptide moiety. In PGM electrostatic interactions between charged end groups apparently promote folded conformations with participation of the long Dap side chain. Derivatives wherein such interactions are suppressed by acylation of the Dap(3)- epsilon amino group are characterized by more extended conformations of the peptide chain. The new synthetic derivatives exhibit biological properties similar to those of the parent PGM. This may indicate that peripheral parts of the peptide chain such as the C-terminal and end groups of the long Dap side chain do not significantly contribute to the binding to receptors or enzymes participating in the biochemical interactions referred to above.

Reversed-phase high-performance liquid chromatographic method for the determination of peptidoglycan monomers and structurally related peptides and adamantyltripeptides.

The reversed-phase HPLC method using UV detection was developed for the determination of (a) immunostimulating peptidoglycan monomers represented by the basic structure GlcNAc-MurNAc-L-Ala-D-isoGln-meso-DAP(omegaNH(2))-D-Ala-D-Ala (PGM) and two more lipophilic derivatives, Boc-Tyr-PGM and (Ada-1-yl)-CH(2)-CO-PGM, (b) two diastereomeric immunostimulating adamantyltripeptides L- and D-(adamant-2-yl)-Gly-L-Ala-D-isoGln and (c) peptides obtained by the enzyme hydrolyses of peptidoglycans and related peptides. The enzymes used, N-acetylmuramyl-L-alanine amidase and an L,D-aminopeptidase are present in mammalian sera and are involved in the metabolism of peptidoglycans and related peptides. Appropriate solvent systems were chosen with regard to structure and lipophilicity of each compound. As well, different gradient systems within the same solvent system had to be applied in order to achieve satisfactory separation and retention time. HPLC separation was developed with the aim to use this method for the study of the stability of the tested compounds, the purity during preparation and isolation and for following the enzyme hydrolyses.