A comparative 1H-n.m.r. study of MurNAc-L-Ala-D-iGln (MDP) and its analogue murabutide: evidence for a structure involving two successive beta-turns in MDP

Investigation of chemical transformations of thiophenylglycoside of muramyl dipeptide on the fumed silica surface using TPD-MS, FTIR spectroscopy and ES IT MS

In this study, chemical transformations of benzyl ester of О-(phenyl-2-acetamido-2,3-dideoxy-1-thio-β-d-glucopyranoside-3-yl)-d-lactoyl-l-alanyl-d-isoglutamine (SPhMDPOBn) on the fumed silica surface were examined, and the surface complex structure was characterized by temperature-programmed desorption mass spectrometry (TPD-MS), infrared spectroscopy (FTIR) and electrospray ion trap mass spectrometry (ES IT MS). Stages of pyrolysis of SPhMDPOBn in pristine state and on the silica surface have been determined. Probably, hydrogen-bonded complex forms between silanol surface groups and the C = O group of the acetamide moiety NH-(CH3)-C = O…H-O-Si≡. The thermal transformations of such hydrogen-bonded complex result in pyrolysis of SPhMDPOBn immobilized on the silica surface under TPD-MS conditions. The shifts ∆ν of amide I band (measured from 1,626 to 1,639 cm(-l) for SPhMDPOBn in pristine state) of 33 and 35 cm(-l) which occurred when SPhMDPOBn was immobilized on the silica surface may be caused by a weakening of the intramolecular hydrogen bonding of the SPhMDPOBn because the interaction with the silica surface as hydrogen bond with silanol groups is weaker than that in associates.

N-[trans-2-[[2'-(acetylamino)cyclohexyl]oxy]acetyl]-L-alanyl-D-glutamic acid: a novel immunologically active carbocyclic muramyl dipeptide analogue

A novel non-pyrogenic carbocyclic muramyl dipeptide (MDP) analogue, N-¿trans-2-[[2'-(acetylamino)cyclohexyl]oxy]acetyl¿-L-alanyl-D-glutamic acid, was obtained by replacement of the N-acetylmuramic acid part and the D-isoglutamine residue of the MDP molecule by a trans-2-[[2'-(acetylamino)cyclohexyl]oxy]acetyl moiety and D-glutamic acid, respectively. The title compound was selected as a promising candidate for further evaluation among several related analogues on the basis of an immunorestoration test in mice. This novel nor-MDP analogue protects mice against the immunosuppressive effect of cyclophosphamide and increases the nonspecific resistance of mice against fungal infection. It is an immunomodulator which enhances the maturation of lymphocytes B to plasma cells and increases the activity of lymphocytes B and lymphocytes T as well as that of macrophages but does not alter the number of these cells.

Apyrogenic synthetic desmuramyldipeptide, LK-409, with immunomodulatory properties

The synthesis and some immunological characteristics of a new desmuramyl dipeptide 7-oxooctanoyl-L-alanyl-D-isoglutamine (LK-409) are presented. The effects of this compound were compared with those of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP). The influence of LK-409 on the number of B and T cells in spleen and the number of peritoneal macrophages was studied; Jerne's plaque forming cells assay was performed to monitor the effect of B cell differentiation. The blast transformation of T cells stimulated with concanavalin A was used to detect the influences on T lymphocytes. The activation of macrophages was studied as well. In contrast to MDP, LK-409 was apyrogenic in the doses applied but had similar immunomodulatory properties. Tested immunological properties and the absence of pyrogenicity and low toxicity make LK-409 a candidate for an immunomodulatory drug and a model molecule suitable for studying and understanding the dual activity of the MDP and its analogues.

Cooperativity of carbohydrate moiety orientation and beta-turn stability is determined by intramolecular hydrogen bonds in protected glycopeptide models

The 2,3,4,6-Tetra-O-acetyl-beta-D-gluco-, and beta-D-galactopyranosides, as well as approximately 4:1 anomeric mixtures of alpha- and beta-mannopyranosides of Boc-X-Y-NHCH3 dipeptides (X-Y = Pro-Ser, Pro-D-Ser, Val-Ser, Val-D-Ser, and Gly-Ser) have been synthesized. CD and ir spectroscopic studies were performed to characterize the conformation of the glycosylated peptide backbone and examine the possible formation of intrapeptide and glycopeptide intramolecular H-bonds. It was found that O-glycosylated peptides containing a D-serine residue are likely to adopt a type II beta-turn while those with the Pro-Ser or Val-Ser sequence feature a type I (III) beta-turn in solution. Glycosylation also increases the magnitude of the CD bands, characteristic of the given type of beta-turns, which can be interpreted as an indication of the stabilization of the folded backbone conformation. Infrared data showed that in nonpolar solutions the peracetyl glycopeptides adopt both single- and double H-bonded conformations whose ratio, in some cases, depends on the position at C-2' of the H-bond acceptor acetoxy group. These data suggest that five-, seven-, or ten-membered glyco-turns may play an important role in fixing the steric orientation of the carbohydrate antennae systems in glycoproteins.

1H-N.M.R. studies of a natural immunoadjuvant peptidoglycan monomer: proposed structure in solution in methyl sulfoxide

The conformation in solution in methyl sulfoxide of the immunoadjuvant peptidoglycan monomer (PGM), obtained by digestion with lysozyme of the linear peptidoglycan polymer isolated from Brevibacterium divaricatum, was studied by 1H-n.m.r. spectroscopy. The temperature dependence of the chemical shift of the resonances of the amide protons suggested that the amino group of alanine-5 is involved in hydrogen bonding, most probably to the alpha-carbonyl of the isoglutamine which showed restricted rotation, as indicated by the large chemical shift non-equivalence for the resonances of the beta CH2 group. A cyclic structure is proposed for the C-terminal pentapeptide of PGM, which is further supported by various n.O.e. interactions involving the meso-diaminopimelic residue and the N-acetylmuramoyl group.