Design, Synthesis, and Biological Evaluation of Desmuramyl Dipeptides Modified by Adamantyl-1,2,3-triazole.

Muramyl dipeptide (MDP) is the smallest peptidoglycan fragment able to trigger the immune response. Structural modification of MDP can lead to the preparation of analogs with improved immunostimulant properties, including desmuramyl peptides (DMPs). The aim of this work was to prepare the desmuramyl peptide (L-Ala-D-Glu)-containing adamantyl-triazole moiety and its mannosylated derivative in order to study their immunomodulatory activities in vivo. The adjuvant activity of the prepared compounds was evaluated in a murine model using ovalbumin as an antigen, and compared to the reference adjuvant ManAdDMP. The results showed that the introduction of the lipophilic adamantyl-triazole moiety at the C-terminus of L-Ala-D-Glu contributes to the immunostimulant activity of DMP, and that mannosylation of DMP modified with adamantyl-triazole causes the amplification of its immunostimulant activity.

Adamantyl pyran-4-one derivatives and their in vitro antiproliferative activity.

Pyran-4-one (maltol, kojic acid and chlorokojic acid 1) esters of adamantan-1-ylacetic acid were prepared through efficient synthetic routes in good yields and evaluated for their in vitro antiproliferative activity on four cancer cell lines: K562 (chronic myelogenous leukemia), HeLa (cervical cancer), Caco-2 (colorectal adenocarcinoma) and NCI-H358 (bronchioalveolar carcinoma). The results indicate that the presence and the position of the adamantyl acyl group or chlorine atom are the necessary requirement for antitumor activity of pyranone systems. Derivatives of kojic acid with either free (compounds 1 and 8) or acylated 5-OH group (compounds 2 and 9) have shown good-to-moderate activity (IC50 values ranging from 13.1 to 43.0 µM) on all cell lines. Adamantyl kojic acid derivative 5 with a free OH group on the position 2 showed activity only on the K562 cell line. It seems that removal of halogen or adamantyl unit from position 2 elicits antileukemic activity, as observed in compound 5. The positive influence of the adamantyl unit was also observed on a 3-OH acylated derivative of maltol I which was also selectively active on the same cell line. 5-O-benzylated adamantyl compounds 6 and 7 and unmodified starting pyranones were found to be inactive. Antibacterial activity of compounds was also evaluated on S. aureus ATCC 13709, M. catarrhalis ATCC 23246, E. faecalis ATCC29212 and E. coli TolC-Tn10, but no activity was observed (MIC values 128-256 µg/mL).

Adamantane Containing Peptidoglycan Fragments Enhance RANTES and IL-6 Production in Lipopolysaccharide-Induced Macrophages.

We report the enhancement of the lipopolysaccharide-induced immune response by adamantane containing peptidoglycan fragments in vitro. The immune stimulation was detected by Il-6 (interleukine 6) and RANTES (regulated on activation, normal T cell expressed and secreted) chemokine expression using cell assays on immortalized mouse bone-marrow derived macrophages. The most active compound was a α-D-mannosyl derivative of an adamantylated tripeptide with L-chirality at the adamantyl group attachment, whereby the mannose moiety assumed to target mannose receptors expressed on macrophage cell surfaces. The immune co-stimulatory effect was also influenced by the configuration of the adamantyl center, revealing the importance of specific molecular recognition event taking place with its receptor. The immunostimulating activities of these compounds were further enhanced upon their incorporation into lipid bilayers, which is likely related to the presence of the adamantyl group that helps anchor the peptidoglycan fragment into lipid nanoparticles. We concluded that the proposed adamantane containing peptidoglycan fragments act as co-stimulatory agents and are also suitable for the preparation of lipid nanoparticle-based delivery of peptidoglycan fragments.

Synthesis and In Vitro Screening of Novel Heterocyclic ß-d-Gluco- and ß-d-Galactoconjugates as Butyrylcholinesterase Inhibitors.

The development of selective butyrylcholinesterase (BChE) inhibitors may improve the treatment of Alzheimer's disease by increasing lower synaptic levels of the neurotransmitter acetylcholine, which is hydrolysed by acetylcholinesterase, as well as by overexpressed BChE. An increase in the synaptic levels of acetylcholine leads to normal cholinergic neurotransmission and improved cognitive functions. A series of 14 novel heterocyclic ß-d-gluco- and ß-d-galactoconjugates were designed and screened for inhibitory activity against BChE. In the kinetic studies, 4 out of 14 compounds showed an inhibitory effect towards BChE, with benzimidazolium and 1-benzylbenzimidazolium substituted ß-d-gluco- and ß-d-galacto-derivatives in a 10-50 micromolar range. The analysis performed by molecular modelling indicated key residues of the BChE active site, which contributed to a higher affinity toward the selected compounds. Sugar moiety in the inhibitor should enable better blood-brain barrier permeability, and thus increase bioavailability in the central nervous system of these compounds.

Design, synthesis and biological evaluation of immunostimulating mannosylated desmuramyl peptides.

Muramyl dipeptide is the minimal structure of peptidoglycan with adjuvant properties. Replacement of the N-acetylmuramyl moiety and increase of lipophilicity are important approaches in the preparation of muramyl dipeptide analogues with improved pharmacological properties. Mannose receptors present on immunocompetent cells are pattern-recognition receptors and by mannose ligands binding they affect the immune system. Here we present the design, synthesis and biological evaluation of novel mannosylated desmuramyl peptide derivatives. Mannose was coupled to dipeptides containing a lipophilic adamantane on N- or C-terminus through a glycolyl or hydroxyisobutyryl linker. Adjuvant activities of synthesized compounds were investigated in the mouse model using ovalbumin as an antigen. Their activities were compared to the previously described mannosylated adamantane-containing desmuramyl peptide and peptidoglycan monomer. Tested compounds exhibited adjuvant activity and the strongest enhancement of IgG production was stimulated by compound 21 (Man-OCH2-ᴅ-(1-Ad)Gly-ʟ-Ala-ᴅ-isoGln).

A comprehensive evaluation of novel oximes in creation of butyrylcholinesterase-based nerve agent bioscavengers.

A well-considered treatment of acute nerve agents poisoning involves the exogenous administration of butyrylcholinesterase (BChE, EC 3.1.1.8) as a stoichiometric bioscavenger efficient in preventing cholinergic crises caused by acetylcholinesterase (AChE, EC 3.1.1.7) inhibition. An additional improvement in medical countermeasures would be to use oximes that could reactivate BChE as well to upgrade bioscavenging from stoichiometric to oxime-assisted catalytic. Therefore, in this paper we investigated the potency of 39 imidazolium and benzimidazolium oximes (36 compounds synthesized for the first time) to be considered as the reactivators specifically designed for reactivation of phosphylated human BChE. Their efficiency in the reactivation of paraoxon-, VX-, and tabun-inhibited human BChE, as well as human AChE was tested and compared with the efficiencies of HI-6 and obidoxime, used in medical practice today. A comprehensive analysis was performed for the most promising oximes defining kinetic parameters of reactivation as well as interactions with uninhibited BChE. Furthermore, experimental data were compared with computational studies (docking, QSAR analysis) as a starting point in future oxime structure refinement. Considering the strict criteria set for in vivo applications, we determined the cytotoxicity of lead oximes on two cell lines. Among the tested oxime library, one imidazolium compound was selected for preliminary in vivo antidotal study in mice. The obtained protection in VX poisoning outlines its potential in development oxime-assisted OP-bioscavenging with BChE.

Surface modified liposomes by mannosylated conjugates anchored via the adamantyl moiety in the lipid bilayer.

The aim of the present study was to encapsulate mannosylated 1-aminoadamantane and mannosylated adamantyltripeptides, namely [(2R)-N-(adamant-1-yl)-3-(α,ß-d-mannopyranosyloxy)-2-methylpropanamide and (2R)-N-[3-(α-d-mannopyranosyloxy)-2-methylpropanoyl]-d,l-(adamant-2-yl)glycyl-l-alanyl-d-isoglutamine] in liposomes. The characterization of liposomes, size and surface morphology was performed using dynamic light scattering (DLS) and atomic force microscopy (AFM). The results have revealed that the encapsulation of examined compounds changes the size and surface of liposomes. After the concanavalin A (ConA) was added to the liposome preparation, increase in liposome size and their aggregation has been observed. The enlargement of liposomes was ascribed to the specific binding of the ConA to the mannose present on the surface of the prepared liposomes. Thus, it has been shown that the adamantyl moiety from mannosylated 1-aminoadamantane and mannosylated adamantyltripeptides can be used as an anchor in the lipid bilayer for carbohydrate moiety exposed on the liposome surface.

Adamantane-substituted guanylhydrazones: novel inhibitors of butyrylcholinesterase.

A series of novel adamantane-substituted guanylhydrazones was synthesized and used in a study of inhibitory potential toward butyrylcholinesterase. The experimental results were further supported by using docking studies to examine the behavior of the inhibitors within the active site regions of the enzyme. The enzyme-inhibitor dissociation constants K(i) were determined from Hunter-Downs diagrams using Ellman's method for cholinesterase activity determination. Compounds 2-(N-guanidino)iminoadamantane hydrochloride (1) and 2,4-bis(N,N'-guanidino)iminoadamantane dihydrochloride (2) were found to be the best BChE inhibitors and their affinities for the enzyme active site were about five times higher compared to the enzyme peripheral site. The strongest interaction observed in complexes obtained by docking studies was the H-bond between the guanidine and the carboxylate of Glu199 and the second guanidine group in bisguanidine compounds was stabilized with additional H-bonds.

Synthesis and immunostimulating properties of novel adamant-1-yl tripeptides.

The aim of this work was to prepare L- and D-(adamant-1-yl)-Gly-L-Ala-D-isoGln peptides in order to study their adjuvant (immunostimulating) activities. Adjuvant activity of adamant-1-yl tripeptides was tested in the mouse model using ovalbumin as an antigen and in comparison to the peptidoglycan monomer (PGM; ß-D-GlcNAc-(1→4)-D-MurNAc-L-Ala-D-isoGln-mesoDAP(εNH(2) )-D-Ala-D-Ala) and structurally related adamant-2-yl tripeptides.

Influence of mannosylation on immunostimulating activity of adamant-1-yl tripeptide.

The mannosylated derivative of adamant-1-yl tripeptide (D-(Ad-1-yl)Gly-L-Ala-D-isoGln) was prepared to study the effects of mannosylation on adjuvant (immunostimulating) activity. Mannosylated adamant-1-yl tripeptide (Man-OCH(2) CH(Me)CO-D-(Ad-1-yl)Gly-L-Ala-D-isoGln) is a non-pyrogenic, H(2) O-soluble, and non-toxic compound. Adjuvant activity of mannosylated adamantyl tripeptide was tested in the mouse model with ovalbumin as an antigen and in comparison to the parent tripeptide and peptidoglycan monomer (PGM, ß-D-GlcNAc-(1→4)-D-MurNAc-L-Ala-D-isoGln-mesoDAP(εNH(2) )-D-Ala-D-Ala), a well-known effective adjuvant. The mannosylation of adamantyl tripeptide caused the amplification of its immunostimulating activity in such a way that it was comparable to that of PGM.

Preparation of novel meta- and para-substituted N-benzyl protected quinuclidine esters and their resolution with butyrylcholinesterase.

Since the optically active quinuclidin-3-ol is an important intermediate in the preparation of physiologically or pharmacologically active compounds, a new biocatalytic method for the production of chiral quinuclidin-3-ols was examined. Butyrylcholinesterase (BChE; EC 3.1.1.8) was chosen as a biocatalyst in a preparative kinetic resolution of enantiomers. A series of racemic, (R)- and (S)-esters of quinuclidin-3-ol and acetic, benzoic, phthalic and isonicotinic acids were synthesized, as well as their racemic quaternary N-benzyl, meta- and para-N-bromo and N-methylbenzyl derivatives. After the resolution, all N-benzyl protected groups were successfully removed by catalytic transfer hydrogenation with ammonium formate (10% Pd-C). Hydrolyses studies with BChE confirmed that (R)-enantiomers of the prepared esters are much better substrates for the enzyme than (S)-enantiomers. Introduction of bromine atom or methyl group in the meta or para position of the benzyl moiety resulted in a considerable improvement of the stereoselectivity compared to the non-substituted compounds. Optically pure quinuclidin-3-ols were prepared in high yields and enantiopurity by the usage of various N-benzyl protected groups and BChE as a biocatalyst.

Targeted Delivery of Adamantylated Peptidoglycan Immunomodulators in Lipid Nanocarriers: NMR Shows That Cargo Fragments Are Available on the Surface.

We present an in-depth investigation of the membrane interactions of peptidoglycan (PGN)-based immune adjuvants designed for lipid-based delivery systems using NMR spectroscopy. The derivatives contain a cargo peptidoglycan (PGN) dipeptide fragment and an adamantyl group, which serves as an anchor to the lipid bilayer. Furthermore, derivatives with a mannose group that can actively target cell surface receptors on immune cells are also studied. We showed that the targeting mannose group and the cargo PGN fragment are both available on the lipid bilayer surface, thereby enabling interactions with cognate receptors. We found that the nonmannosylated compounds are incorporated stronger into the lipid assemblies than the mannosylated ones, but the latter compounds penetrate deeper in the bilayer. This might be explained by stronger electrostatic interactions available for zwitterionic nonmannosylated derivatives as opposed to the compounds in which the charged N-terminus is capped by mannose groups. The higher incorporation efficiency of the nonmannosylated compounds correlated with a larger relative enhancement in immune stimulation activities upon lipid incorporation compared to that of the derivatives with the mannose group. The chirality of the adamantyl group also influenced the incorporation efficiency, which in turn correlated with membrane-associated conformations that affect possible intermolecular interactions with lipid molecules. These findings will help in improving the development of PGN-based immune adjuvants suitable for delivery in lipid nanoparticles.

Novel mannosyl derivatives of peptidoglycan monomer: Synthesis and biological evaluation of immunomodulatory properties.

The aim of this work was to prepare mannosyl derivatives of peptidoglycan monomer (PGM, beta-d-GlcNAc-(1-->4)-d-MurNAc-l-Ala-d-isoGln-mesoDAP(epsilonNH(2))-d-Ala-d-Ala) in order to study the effects of mannosylation on adjuvant (immunostimulating) activity. Novel Man-OCH(2)CH(CH(3))CO-PGM isomers were substrates for N-acetylmuramyl-l-alanine amidase, like the parent PGM molecule. Adjuvant activity of Man-OCH(2)CH(CH(3))CO-PGM was tested in the mouse model using ovalbumin as an antigen.

Synthesis and intramolecular transesterifications of pivaloylated methyl alpha-D-galactopyranosides.

Selective pivaloylations of methyl alpha-D-galactopyranoside have been studied under various reaction conditions. Partially pivaloylated products were submitted to additional acetylations. The structures were established by 1H and 13C NMR spectroscopies. Both, 2,6- and 3,6-dipivalates underwent intramolecular cyclization in neutral conditions (phosphate buffered saline, pH 7.2) to give a stable 2,3-orthoacid with a parallel 6-->4 migration of the pivaloyl group.

Synthesis, intramolecular migrations and enzymic hydrolysis of partially pivaloylated methyl alpha-D-mannopyranosides.

A series of methyl O-pivaloyl-alpha-D-mannopyranosides was synthesized using pivaloyl chloride in pyridine. The 3,6-di-O-pivaloyl derivative 6 undergoes intramolecular transesterification in neutral conditions (buffer, pH 7.2) to give its 2,6-di-O-pivaloyl analogue 5. The course of this migration was followed using 14C-labelled 6. As opposed to 6 compound 5 was shown to be a good substrate for esterases present in rabbit serum. Thus, regioselective enzymic hydrolysis led to the preferential cleavage of the 2-OPiv group to yield a mixture of 2- and 6-O-monopivalates in a ratio of 1:2.6.

Mannosylated N-aryl substituted 3-hydroxypyridine-4-ones: synthesis, hemagglutination inhibitory properties, and molecular modeling.

Structural alterations of the aglycon portions of α-mannosides influence their inhibitory potency toward type 1-fimbriated Escherichia coli. The aim of our work was to prepare and explore inhibitory properties of novel mannosylated N-aryl-substituted 3-hydroxypyridine-4-ones because they possess needed structural characteristics as possible FimH antagonists. Hemagglutination inhibitory tests showed that the examined 3-hydroxypyridine-4-one α-mannosides exhibited better inhibitory activity than methyl α-d-mannopyranoside used as a reference compound. Molecular modeling studies revealed the specific interactions responsible for the observed binding activities toward the mannose-specific FimH lectin. The activity depends on the substituent in p-position on the aglycon aromatic ring.

3-Amidoquinuclidine derivatives: synthesis of compounds and inhibition of butyrylcholinesterase.

The synthesis of racemic and enantiomerically pure 3-butanamidoquinuclidines ((+/-)-Bu, (R)-Bu and (S)-Bu), (1-3) and 3-benzamidoquinuclidines ((+/-)-Bz, (R)-Bz, and (S)-Bz), (4-6) is described. The N-quaternary derivatives, N-benzyl-3-butanamidoquinuclidinium bromides ((+/-)-BnlBu, (R)-BnlBu and (S)-BnlBu), (7-9) and N-benzyl-3-benzamidoquinuclidinium bromides ((+/-)-BnlBz, (R)-BnlBz and (S)-BnlBz), (10-12) were subsequently synthesized. The interaction of the four enantiomerically pure quaternary derivatives with horse serum butyrylcholinesterase (BChE) was tested. All tested compounds inhibited the enzyme. The best inhibitior of the enzyme was (S)-BnlBz with a K(i) = 3.7 microM. The inhibitor potency decreases in order (S)-BnlBz > (R)-BnlBz >> (R)-BnlBu > (S)-BnlBu.