1.Preparation of S-glycoside surfactants and cysteine thioglycosides using minimally competent Lewis acid catalysis.
Szabó LZ1, Hanrahan DJ1, Jones EM1, Martin E1, Pemberton JE1, Polt R2. Carbohydr Res. 2016 Mar 3;422:1-4. doi: 10.1016/j.carres.2015.12.008. Epub 2016 Jan 6.
Here we report a method for the preparation of anomerically pure β-S-glycopyranosides (1,2-trans-glycosides) from the corresponding peracetate donors. S-glycosylation was performed in CHCl3 at reflux in the presence of a catalytic amount of InBr3. Deacylation of the intermediate peracetates were achieved under Zemplén conditions. Five pyranose examples, monosaccharides D-glucose and D-galactose and disaccharides cellobiose, maltose, and lactose, were used as donors, and five thiols including an α/ω dithiol and Fmoc-L-cysteine were used as acceptors. Melting points, high res MS, [α]D and NMR data ((1)H and (13)C, including COSY, HSQC and HMBC) are reported for compounds not previously described.
2.Rapid acidolysis of benzyl group as a suitable approach for syntheses of peptides naturally produced by oxidative stress and containing 3-nitrotyrosine.
Niederhafner P1,2, Šafařík M2, Brichtová E2, Šebestík J3. Amino Acids. 2016 Apr;48(4):1087-98. doi: 10.1007/s00726-015-2163-2. Epub 2016 Jan 14.
3-Nitrotyrosine (Nit) belongs to products of oxidative stress and could probably influence conformation of neurodegenerative proteins. Syntheses of peptides require availability of suitable synthon for introduction of Nit residue. Common phenolic protection groups are more acid labile, when they are attached to Nit residue. We have found that Fmoc-Nit(Bn)-OH is a good building block for syntheses of Nit containing peptides by Fmoc/tBu strategy. Interestingly, the peptides containing multiple Nit residues can be available solely by use of Fmoc-Nit(Bn)-OH synthon. Bn is removed rapidly with ca 80 % trifluoroacetic acid in dark. The cleavage of Bn from Fmoc-Nit(Bn)-OH proceeds via pseudo-first order mechanism with activation barrier 32 kcal mol(-1) and rate k = 15.3 s(-1) at 20 °C. This rate is more than 2,000,000 times faster than that for cleavage of benzyl from Tyr(Bn).
3.Analysis of glyphosate and aminomethylphosphonic acid in leaves from Coffea arabica using high performance liquid chromatography with quadrupole mass spectrometry detection.
Schrübbers LC1, Masís-Mora M2, Rojas EC2, Valverde BE3, Christensen JH4, Cedergreen N4. Talanta. 2016 Jan 1;146:609-20. doi: 10.1016/j.talanta.2015.07.059. Epub 2015 Jul 20.
Glyphosate is a commonly applied herbicide in coffee plantations. Because of its non-selective mode of action it can damage the crop exposed through spray drift. Therefore, it is of interest to study glyphosate fate in coffee plants. The aim of this study was to develop an analytical method for accurate and precise quantification of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) at trace levels in coffee leaves using liquid chromatography with single-quadrupole mass spectrometry detection. The method is based on a two-step solid phase extraction (SPE) with an intermediate derivatization reaction using 9-fluorenylmethylchloroformate (FMOC). An isotope dilution method was used to account for matrix effects and to enhance the confidence in analyte identification. The limit of quantification (LOQ) for glyphosate and AMPA in coffee leaves was 41 and 111 μg kg(-1) dry weight, respectively. For the method optimization a design of experiments (DOE) approach was used.
4.Sequence Adaptive Peptide-Polysaccharide Nanostructures by Biocatalytic Self-Assembly.
Abul-Haija YM1, Ulijn RV1,2. Biomacromolecules. 2015 Nov 9;16(11):3473-9. doi: 10.1021/acs.biomac.5b00893. Epub 2015 Oct 12.
Coassembly of peptides and polysaccharides can give rise to the formation of nanostructures with tunable morphologies. We show that in situ enzymatic exchange of a dipeptide sequence in aromatic peptide amphiphiles/polysaccharide coassemblies enables dynamic formation and degradation of different nanostructures depending on the nature of the polysaccharide present. This is achieved in a one-pot system composed of Fmoc-cysteic acid (CA) and Fmoc-lysine (K) plus phenylalanine amide (F) in the presence of thermolysin that, through dynamic hydrolysis and amide formation, gives rise to a dynamic peptide library composed of the corresponding Fmoc-dipeptides (CAF and KF). When the cationic polysaccharide chitosan is added to this mixture, selective amplification of the CAF peptide is observed giving rise to formation of nanosheets through coassembly. By contrast, upon addition of anionic heparin, KF is formed that gives rise to a nanotube morphology.
