Synthesis and Crystallographic Characterization of Helical Hairpin Oligourea Foldamers.

Invited for the cover of this issue is the group of Gilles Guichard at the University of Bordeaux. The image depicts sketches and technical drawing tools to illustrate the creation and precise characterization of foldamer tertiary structures. Read the full text of the article at 10.1002/chem.202300087.

Synthesis and Crystallographic Characterization of Helical Hairpin Oligourea Foldamers.

Oligomers designed to form a helix-turn-helix super-secondary structure have been prepared by covalently bridging aliphatic oligourea foldamer helices with either rigid aromatic or more flexible aliphatic spacers. The relative helix orientation in these dimers was investigated at high resolution using X-ray diffraction analysis. In several cases, racemic crystallography was used to facilitate crystallization and structure determination. All structures were solved by direct methods. Well-defined parallel helical hairpin motifs were observed in all cases when 4,4'-methylene diphenyl diisocyanate was employed as a dimerizing agent, irrespective of primary sequence and chain length.

Newborn Screening for Mucopolysaccharidoses: Results of a Pilot Study with 100 000 Dried Blood Spots.

OBJECTIVE: To test, in a newborn screening (NBS) laboratory, the performance of liquid chromatography-tandem mass spectrometry (LC-MS/MS) to assay 5 enzymatic activities in dried blood spots (DBS) for NBS of 5 lysosomal storage diseases (mucopolysaccharidosis [MPS]-II, MPS-IIIB, MPS-IVA, MPS-VI, and MPS-VII). STUDY DESIGN: Three mm punches from de-identified DBS were obtained from the Washington NBS laboratory and submitted to the 5-plex LC-MS/MS assay. Screen cut-offs were established by analyzing the enzymatic activity in patients confirmed to have the MPS disorder. DNA sequencing of the relevant gene was performed on a second DBS punch for all samples with enzyme activity below 10% of the mean daily activity. RESULTS: (1) For MPS-II, 18 below cut-off samples, 1 pathogenic genotype, and 2 "high risk" genotypes; (2) For MPS-IIIB, no below cut-off samples; (3) For MPS-IVA, 8 below cut-off samples, 4 non-pathogenic genotypes, 4 genotypes unobtainable; (4) For MPS-VI, 4 below cut-off samples and no high-risk genotypes; (5) For MPS-VII, 1 below cut-off sample confirmed by genotype and clinical report to be affected. CONCLUSIONS: These results establish that the number of initial screen positive samples is low and manageable. Thus, population newborn screening for these conditions is feasible in a state newborn screening laboratory.

Taiwan National Newborn Screening Program by Tandem Mass Spectrometry for Mucopolysaccharidoses Types I, II, and VI.

OBJECTIVE: To evaluate the initial cutoff values, rates of screen positives, and genotypes for the large-scale newborn screening program for multiple mucopolysaccharidoses (MPS) in Taiwan. STUDY DESIGN: More than 100 000 dried blood spots were collected consecutively as part of the national Taiwan newborn screening programs. Enzyme activities were measured by tandem mass spectrometry from dried blood spot punches. Genotypes were obtained when a second newborn screening specimen again had a decreased enzyme activity. Additional clinical evaluation was then initiated based on enzyme activity and/or genotype. RESULTS: Molecular genetic analysis for cases with low enzyme activity revealed 5 newborns with pathogenic alpha-L-iduronidase mutations, 3 newborns with pathogenic iduronate-2-sulfatase mutations, and 1 newborn was a carrier of an arylsulfatase B mutation. Several variants of unknown pathogenic significance were also identified, most likely causing pseudodeficiency. CONCLUSIONS: The highly robust tandem mass spectrometry-based enzyme assays for MPS-I, MPS-II, and MPS-VI allow for high-throughput newborn screening for these lysosomal storage disorders. Optimized cutoff values combined with second tier testing could largely eliminate false-positive results. Accordingly, newborn screening for these lysosomal storage disorders is possible.

Helix-forming propensity of aliphatic urea oligomers incorporating noncanonical residue substitution patterns.

Aliphatic N,N'-linked oligoureas are peptidomimetic foldamers that adopt a well-defined helical secondary structure stabilized by a collection of remote three-center H-bonds closing 12- and 14-membered pseudorings. Delineating the rules that govern helix formation depending on the nature of constituent units is of practical utility if one aims to utilize this helical fold to place side chains in a given arrangement and elaborate functional helices. In this work, we tested whether the helix geometry is compatible with alternative substitution patterns. The central -NH-CH(R)-CH2-NH-CO- residue in a model oligourea pentamer sequence was replaced by guest units bearing various substitution patterns [e.g., -NH-CH2-CH2-NH-CO-, -NH-CH2-CH(R)-NH-CO-, and -NH-CH(R(1))-CH(R(2))-NH-CO-], levels of preorganization (cyclic vs acyclic residues), and stereochemistries, and the helix formation was systematically assessed. The extent of helix perturbation or stabilization was primarily monitored in solution by Fourier transform IR, NMR, and electronic circular dichroism spectroscopies. Our results indicate that although three new substitution patterns were accommodated in the 2.5-helix, the helical urea backbone in short oligomers is particularly sensitive to variations in the residue substitution pattern (position and stereochemistry). For example, the trans-1,2-diaminocyclohexane unit was experimentally found to break the helix nucleation, but the corresponding cis unit did not. Theoretical calculations helped to rationalize these results. The conformational preferences in this series of oligoureas were also studied at high resolution by X-ray structure analyses of a representative set of modified oligomers.

Solid state NMR studies of oligourea foldamers: interaction of 15N-labelled amphiphilic helices with oriented lipid membranes.

Synthetic oligomers that are derived from natural polypeptide sequences, albeit with unnatural building blocks, have attracted considerable interest in mimicking bioactive peptides and proteins. Many of those compounds adopt stable folds in aqueous environments that resemble protein structural elements. Here we have chemically prepared aliphatic oligoureas and labeled them at selected positions with (15)N for structural investigations using solid-state NMR spectroscopy. In the first step, the main tensor elements and the molecular alignment of the (15)N chemical shift tensor were analyzed. This was possible by using a two-dimensional heteronuclear chemical shift/dipolar coupling correlation experiment on a model compound that represents the chemical, and thereby also the chemical shift characteristics, of the urea bond. In the next step (15)N labeled versions of an amphipathic oligourea, that exert potent antimicrobial activities and that adopt stable helical structures in aqueous environments, were prepared. These compounds were reconstituted into oriented phospholipid bilayers and the (15)N chemical shift and (1)H-(15)N dipolar couplings of two labeled sites were determined by solid-state NMR spectroscopy. The data are indicative of an alignment of this helix parallel to the membrane surface in excellent agreement with the amphipathic character of the foldamer and consistent with previous models explaining the antimicrobial activities of α-peptides.

5-Fluoroimidazo[4,5-b]pyridine Is a Privileged Fragment That Conveys Bioavailability to Potent Trypanosomal Methionyl-tRNA Synthetase Inhibitors.

Fluorination is a well-known strategy for improving the bioavailability of drug molecules. However, its impact on efficacy is not easily predicted. On the basis of inhibitor-bound protein crystal structures, we found a beneficial fluorination spot for inhibitors targeting methionyl-tRNA synthetase of Trypanosoma brucei. In particular, incorporating 5-fluoroimidazo[4,5-b]pyridine into inhibitors leads to central nervous system bioavailability and maintained or even improved efficacy.