Constrained beta-amino acid-containing miniproteins.

The construction of ß-amino acid-containing peptides that fold to tertiary structures in solution remains challenging. Two model miniproteins, namely, Trp-cage and FSD, were scanned using a constrained ß-amino acid in order to evaluate its impact on the folding process. Relationships between forces stabilizing the miniprotein structure and conformational stability of analogues were found. The possibility of a significant increase of the conformational stability of the studied miniproteins by substitution with the ß-amino acid at the terminus of a helix is shown. On the basis of these results, ß-amino acid containing-peptide analogs with helical fragments substantially altered by the incorporation of several constrained ß-amino acids were designed, synthesized and evaluated with respect to their structure and stability. The smallest known ß-amino acid-containing peptide with a well-defined tertiary structure is described.

Modulating effect of a new ester, 28-O-phosphatidylbetulin (DAPB), obtained from hen egg yolk lecithin and betulin on lymphocyte subsets and humoral immune response in mice.

Context: Leaf extracts of plants of the genus Betula have traditionally been used as diuretic, anti-rheumatic and diaphoretic preparations. One of the main active ingredients of Betula bark is betulin, lupane-type triterpene alcohol, with multiple biological activities. Objectives: The aim of this study was to investigate in vitro and in vivo immunomodulatory effects of a newly synthesized ester of betulin: 28-O-phosphatidylbetulin [28-O-(1,2-diacyl-sn-glycero-3-phospho)-betulin, DAPB] in comparison with betulin in mice. Materials and methods: Cytotoxic activity of DAPB or betulin was tested against non-cancer (D10.G4.1 and J774E.1) and cancer (GL-1; CL-1 and Jurkat) cell lines. The in vivo part assessed total lymphocyte count, weight ratio and subsets of lymphocytes in the lymphatic organs, and humoral immune response to sheep erythrocytes (SRBC). Results: In vitro assay showed that DAPB, contrary to betulin, had no antiproliferative activity. Exposure to four doses of DAPB increased the absolute count of immature CD4+CD8+ thymic cells as well as the percentage and absolute count of mature CD4+ and CD8+ thymocytes. DAPB enhanced the percentage or absolute count of CD3+ cells in spleen and lymph nodes with corresponding decrease in the percentage and/or absolute count of CD19+ cells. Both DAPB and betulin enhanced the percentage and absolute count of CD8+ lymphocytes in lymph nodes. In SRBC-immunized mice, betulin contrary to DAPB enhanced the number of splenocytes producing anti-SRBC antibodies (PFC). Both DAPB and betulin increased the level of total (IgM + IgG) and IgG titers. Conclusion: Despite the lack of cytotoxic activity, DAPB shows valuable immunomodulatory properties.

4'-Methoxyphenacyl-Assisted Synthesis of ß-Kdo Glycosides.

3-Deoxy-ß-d-manno-oct-2-ulosonic acid (ß-Kdo) glycosides are mainly found in capsular polysaccharides and extracellular exopolysaccharides from Gram-negative bacteria. These compounds have profound biological implications in immune response and act as virulence factors. We have developed a novel methodology for the stereoselective synthesis of ß-Kdo glycosides via the use of a 4'-methoxyphenacyl (Phen) auxiliary group at the C1 position of a peracetylated ß-Kdo thioglycoside. Under the promotion of NIS/AgOTf in acetonitrile, a series of Kdo glycosides was synthesized in good yield and ß-selectivity while minimizing the formation of undesirable glycals. Stereoselectivity of the glycosylation was shown to be modulated by various factors such as promotor, solvent, anomeric ratio of donor, nature of acceptor, and Phen substitution. Chemoselective cleavage of the Phen group was performed under the action of Zn/HOAc. DFT calculations together with experimental results suggested that α-triflate and a six-membered α-spiroPhen are plausible intermediates of the reaction, accounting for the enhanced formation of ß-Kdo glycosides. The developed methodology could be applied to the synthesis of ß-Kdo-containing glycans from pathogenic bacteria.

Synthesis of the Tetrasaccharide Repeating Unit of the ß-Kdo-Containing Exopolysaccharide from Burkholderia pseudomallei and B. cepacia Complex.

The synthesis of the repeating unit of the immunogenic ß-Kdo-containing exopolysaccharide produced by Burkholderia pseudomallei and bacteria of the B. cepacia complex is described. The target tetrasaccharide was synthesized via stereoselective 1,2-cis- and 1,2-trans-galactosylations and ß-Kdosylation. A [3 + 1] coupling reaction between a trigalactosyl N-phenyl-2,2,2-trifluoroacetimidate donor and a Kdo acceptor has been successfully achieved for the assembly of the tetrasaccharide skeleton.