Branching of poly(ADP-ribose): Synthesis of the Core Motif

The synthesis of the core motif of branched poly­(adenosine diphosphate ribose) (poly­(ADPr)) is described, and structural analysis reasserted the proposed stereochemistry for branching. For the synthesis, a ribose trisaccharide was first constructed with only α-<i>O</i>-glycosidic linkages. Finally, the adenine nucleobase was introduced via a Vorbrüggen-type glycosylation reaction. The orthogonality of the selected protecting groups was demonstrated, allowing for the construction of branched poly­(ADPr) oligomers in the near future

Stereoselective Ribosylation of Amino Acids

The glycosylation properties of ribofuranosyl <i>N</i>-phenyltrifluoroacetimidates toward carboxamide side chains of asparagine and glutamine were investigated. Conditions were found that promote nearly exclusive formation of the α-anomerically configured <i>N</i>-glycosides. The strategy allows for the synthesis of Fmoc-amino acids suitably modified for the preparation of ADP-ribosylated peptides. Furthermore, ribosylation of serine with these donors proved to be completely α-selective, and for the first time, α-ribosylated glutamic and aspartic acid, the naturally occurring sites for poly-ADP-ribosylation, were synthesized

Chemoselective Cleavage of <i>p</i>‑Methoxybenzyl and 2‑Naphthylmethyl Ethers Using a Catalytic Amount of HCl in Hexafluoro-2-propanol

A new, fast, mild and chemoselective deprotection method to cleave <i>p</i>-methoxybenzyl and 2-naphthylmethyl ethers using catalytic amounts of hydrochloric acid in a 1:1 mixture of hexafluoro-2-propanol (HFIP) and methylene chloride (DCM) is described. The scope of the methodology becomes apparent from 14 examples of orthogonally protected monosaccharides that are subjected to HCl/HFIP treatment. The applicability of the HCl/HFIP method is illustrated by the synthesis of a sulfated β-mannuronic acid disaccharide

Acylazetine as a Dienophile in Bioorthogonal Inverse Electron-Demand Diels–Alder Ligation

A new bioorthogonal <i>N</i>-acylazetine tag, suitable for tetrazine mediated inverse electron-demand Diels–Alder conjugation, is developed. The tag is small and achiral. We demonstrate the usefulness of <i>N</i>-acylazetine-tetrazine based bioorthogonal chemistry in two-step activity-based protein profiling. The performance of the new tetrazinophile in the labeling of catalytically active proteasome subunits was comparable to that of the more sterically demanding norbornene tag

Stereoselectivity in the Lewis Acid Mediated Reduction of Ketofuranoses

The Lewis acid mediated reduction of ribose-, arabinose-, xylose-, and lyxose-derived methyl and phenyl ketofuranoses with triethylsilane as nucleophile was found to proceed with good to excellent stereoselectivity to provide the 1,2-<i>cis</i> addition products. The methyl ketoses reacted in a more stereoselective manner than their phenyl counterparts. The stereochemical outcome of the reactions parallels the relative stability of the oxocarbenium ion conformers involved, as assessed by calculating the free energy surface maps of their complete conformational space. The Lewis acid mediated reduction allows for a direct synthesis of <i>C</i>-glycosides with predictable stereochemistry

The Optimization of Bioorthogonal Epitope Ligation within MHC‑I Complexes

Antigen recognition followed by the activation of cytotoxic T-cells (CTLs) is a key step in adaptive immunity, resulting in clearance of viruses and cancers. The repertoire of peptides that have the ability to bind to the major histocompatibility type-I (MHC-I) is enormous, but the approaches available for studying the diversity of the peptide repertoire on a cell are limited. Here, we explore the use of bioorthogonal chemistry to quantify specific peptide–MHC-I complexes (pMHC-I) on cells. We show that modifying epitope peptides with bioorthogonal groups in surface accessible positions allows wild-type-like MHC-I binding and bioorthogonal ligation using fluorogenic chromophores in combination with a Cu­(I)-catalyzed Huisgen cycloaddition reaction. We expect that this approach will make a powerful addition to the antigen presentation toolkit as for the first time it allows quantification of antigenic peptides for which no detection tools exist

Design, Synthesis, and Structural Analysis of Turn Modified <i>cyclo</i>-(αβ³αβ²α)₂ Peptide Derivatives toward Crystalline Hexagon-Shaped Cationic Nanochannel Assemblies

Intrigued by the not fully extended hairpin monomeric structure of the previously reported <i>cyclo</i>-(αβ³αβ²α)₂ peptide <b>2</b>, as well as its nanochannel crystallographic assembly, we here investigate the structural properties of a series of turn derivatives (<b>3</b>–<b>17</b>). Five crystallographic monomeric structures of the symmetric and asymmetric <i>cyclo</i>-(αβ³αβ²α)₂ peptides <b>3</b>–<b>17</b> are found; the novel saddlelike (<b>4</b> and <b>16</b>) and the twisted hairpin (<b>6</b>) conformers, as well as the not fully extended hairpins <b>7</b> and <b>14</b>. The pentafluorophenyl/1-naphthyl and pentafluorophenyl/9-phenanthryl derivatives <b>7</b> and <b>14</b>, respectively, adopt the anticipated hexagon-shaped crystalline nanotube assemblies, resembling the crystal packing of the parent peptide <b>2</b>. The structural analysis of the compounds as described here can serve as a basis for biological applications, such as the design of β-sheet mimics or for the development of functional nanomaterials

Statistics of <i>in vivo</i> tumor experiments.

<p>ns: not significant (considered if p>0.05). Exp.: experiment.</p><p>nt: not tested. TFS: tumor-free survival.</p><p>*: Unpaired <i>t</i>-test. CI: CpG & imiquimod.</p><p>**: Logrank test for survival (endpoint tumor size max 200 mm²). MIC: monobenzone, imiquimod & CpG.</p>1<p>:Day of tumor size comparison (last day on which experimental animals were all alive).</p><p>For Exp. 2 see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010626#pone-0010626-g001" target="_blank">Fig. 1A/B</a>, for Exp. 3 see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010626#pone-0010626-g003" target="_blank">Fig. 3C</a> (upper panel), for Exp. 4 see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010626#pone-0010626-g003" target="_blank">Fig. 3A/B and C</a> (lower panel),</p