Tunable Strategy for the Asymmetric Synthesis of Sulfoglycolipids from Mycobacterium tuberculosis To Elucidate the Structure and Immunomodulatory Property Relationships

We developed a versatile asymmetric strategy to synthesize different classes of sulfoglycolipids (SGLs) from Mycobacterium tuberculosis. The strategy features the use of asymmetrically protected trehaloses, which were acquired from the glycosylation of TMS α-glucosyl acceptors with benzylidene-protected thioglucosyl donors. The positions of the protecting groups at the donors and acceptors can be fine-tuned to obtain different protecting-group patterns, which is crucial for regioselective acylation and sulfation. In addition, a chemoenzymatic strategy was established to prepare the polymethylated fatty acid building blocks. The strategy employs inexpensive lipase as a desymmetrization agent in the preparation of the starting substrate and readily available chiral oxazolidinone as a chirality-controlling agent in the construction of the polymethylated fatty acids. A subsequent investigation on the immunomodulatory properties of each class of SGLs showed how the structures of SGLs impact the host innate immunity response.     

Resolving an apparent discrepancy between theory and experiment: spin-spin coupling constants for FCCF

Ab initio equation of motion coupled cluster singles and doubles (EOM-CCSD) and second-order polarization propagator approximation (SOPPA) calculations have been performed to evaluate spin-spin coupling constants for FCCF (difluoroethyne). The computed EOM-CCSD value of (3)J(F-F) obtained at the experimental geometry of this molecule supports the previously reported experimental value of 2.1 Hz, thereby resolving an apparent discrepancy between theory and experiment. This coupling constant exhibits a strong dependence on the C-C and C-F distances, and its small positive value results from a sensitive balance of paramagnetic spin-orbit (PSO) and spin-dipole (SD) terms. The three other unique FCCF coupling constants (1)J(C-C), (1)J(C-F), and (2)J(C-F) have also been reported and compared with experimental data. While (1)J(C-F) is in agreement with experiment, the computed value of (2)J(C-F) is larger than our estimate of the experimental coupling constant.     

Effects of nitrate and water on the oxygen isotopic analysis of barium sulfate precipitated from water samples

BaSO₄ precipitated from mixed salt solutions by common techniques for SO isotopic analysis may contain quantities of H₂O and NO that introduce errors in O isotope measurements. Experiments with synthetic solutions indicate that δ¹⁸O values of CO produced by decomposition of precipitated BaSO₄ in a carbon reactor may be either too low or too high, depending on the relative concentrations of SO and NO and the δ¹⁸O values of the H₂O, NO, and SO. Typical δ¹⁸O errors are of the order of 0.5 to 1‰ in many sample types, and can be larger in samples containing atmospheric NO, which can cause similar errors in δ¹⁷O and Δ¹⁷O. These errors can be reduced by (1) ion chromatographic separation of SO from NO, (2) increasing the salinity of the solutions before precipitating BaSO₄ to minimize incorporation of H₂O, (3) heating BaSO₄ under vacuum to remove H₂O, (4) preparing isotopic reference materials as aqueous samples to mimic the conditions of the samples, and (5) adjusting measured δ¹⁸O values based on amounts and isotopic compositions of coexisting H₂O and NO. These procedures are demonstrated for SO isotopic reference materials, synthetic solutions with isotopically known reagents, atmospheric deposition from Shenandoah National Park, Virginia, USA, and sulfate salt deposits from the Atacama Desert, Chile, and Mojave Desert, California, USA. These results have implications for the calibration and use of O isotope data in studies of SO sources and reaction mechanisms. Published in 2008 by John Wiley & Sons, Ltd.     

Faunal migration in late-glacial central Italy: implications for human resource exploitation

The hunter-gatherer transhumance model presents foragers as specialised hunters of migratory ungulates, which moved seasonally between coastal lowlands and interior uplands. We studied six animal teeth of horse (Equus hydruntinus) and red deer (Cervus elaphus) from four different archaeological sites: the Grotta di Vado all'Arancio, Grotta di Settecannelle, Grotta Polesini and Grotta di Pozzo, in central Italy to test whether the migratory patterns and seasonal variations recorded in their teeth were consistent with expectations of the transhumance model for this region during the late Upper Palaeolithic. Sequential sub-samples of enamel were analysed from each tooth for oxygen, carbon and strontium isotope ratios to reconstruct mobility and yearly seasonal variations. The results show little evidence that these animals were moving over different geological terrains throughout the year, although small variations in Sr isotope ratios and concentrations were detected that corresponded to probable seasonal variations as shown by variability in oxygen isotope sequences. The results do, however, demonstrate that Cervus elaphus and Equus hydruntinus had different ranging behaviours, with the former moving over wider areas than the latter. This methodology produces results appropriate to assess animal migratory behaviour and, in turn, to test the consistency of proposed models of hunter-gatherer subsistence and mobility strategies.     

Normal carbon acid referencing for protein amide hydrogen exchange

Measurement of the exchange kinetics for amide hydrogens along the protein backbone continues to offer valuable insights into structural stability and conformational dynamics. Since such studies routinely compare samples that differ in solution conditions or mechanical handling, normalization of the relative exchange rates can present a potentially significant source of experimental uncertainty. The carbon acids 1,3-dimethylimidazolium cation and thiomethylacetonitrile exhibit base catalyzed exchange rates similar to those of the slowly exchanging amides, under conditions typical for protein studies. With 13C enrichment at the acidic carbon position to facilitate selective observation, such carbon acids offer practical internal calibration of exchange.     

The impact of impurities in synthetic peptides on the outcome of T-cell stimulation assays

Protein-spanning peptide pools have proven valuable as a screening tool for detecting T-lymphocyte responses against a wide range of proteins. We have used this approach in our search for T cells reactive to the onconeural protein HuD. We found positive responses in only 3 of 127 individuals; however, these were highly unusual in that the same class I HLA alleles and peptides were involved. These T-cell responses were not confirmed when peptides re-synthesized by the same manufacturer with similar and with higher purity levels were used. Our observations indicated that these T-cell responses were not directed against the designed HuD peptides. Here, we report on (i) comparisons of the peptide batches analyzed by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) that did--and did not--elicit T-cell responses and (ii) a detailed analysis of the various by-products of peptides, irrespective of T-cell assay outcome. We found numerous differences between the peptide batches, such as omissions of amino acids in the primary structure of the peptides. Furthermore, some batches revealed strong interactions with calcium ions or contained sulfated peptides. Our data reveal that different batches from the same peptide may contain artefacts that influence the outcome of HLA-restricted T-cell response assays.     

A mild Boc deprotection and the importance of a free carboxylate

We report a facile and rapid removal of Boc protecting groups using microwave heating in H₂O, with deprotection only requiring a free carboxylic acid group in the starting material. Unlike previous approaches, no additional reagents are required.     

Tethered dinuclear europium(III) macrocyclic catalysts for the cleavage of RNA

Dinuclear europium(III) complexes of the macrocycles 1,3-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-m-xylene (1), 1,4-bis[1-(4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane]-p-xylene (2), and mononuclear europium(III) complexes of macrocycles 1-methyl-,4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (3), 1-[3'-(N,N-diethylaminomethyl)benzyl]-4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (4), and 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane (5) were prepared. Studies using direct excitation ((7)F0 --> (5)D0) europium(III) luminescence spectroscopy show that each Eu(III) center in the mononuclear and dinuclear complexes has two water ligands at pH 7.0, I = 0.10 M (NaNO3) and that there are no water ligand ionizations over the pH range of 7-9. All complexes promote cleavage of the RNA analogue 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) at 25 degrees C (I = 0.10 M (NaNO3), 20 mM buffer). Second-order rate constants for the cleavage of HpPNP by the catalysts increase linearly with pH in the pH range of 7-9. The second-order rate constant for HpPNP cleavage by the dinuclear Eu(III) complex (Eu2(1)) at pH 7 is 200 and 23-fold higher than that of Eu(5) and Eu(3), respectively, but only 7-fold higher than the mononuclear complex with an aryl pendent group, Eu(4). This shows that the macrocycle substituent modulates the efficiency of the Eu(III) catalysts. Eu2(1) promotes cleavage of a dinucleoside, uridylyl-3',5'-uridine (UpU) with a second-order rate constant at pH 7.6 (0.021 M(-1) s(-1)) that is 46-fold higher than that of the mononuclear Eu(5) complex. Methyl phosphate binding to the Eu(III) complexes is energetically most favorable for the best catalysts, and this supports an important role for the catalyst in stabilization of the developing negative charge on the phosphorane transition state. Despite the formation of a bridging phosphate ester between the two Eu(III) centers in Eu2(1) as shown by luminescence spectroscopy, the two metal ion centers are only weakly cooperative in cleavage of RNA and RNA analogues.     

Age-related changes in sensitivity to native phonotactics in Japanese infants

Japanese infants at the ages of 6, 12, and 18 months were tested on their ability to discriminate three nonsense words with different phonotactic status: canonical keetsu, noncanonical but possible keets, and noncanonical and impossible keet. The results showed that 12 and 18 months olds discriminate the keets/keetsu pair, but infants in all age groups fail to discriminate the keets/keet pair. Taken together with the findings in our previous study [Kajikawa et al., J. Acoust. Soc. Am. 120(4), 2278-2284 (2006)], these results suggest that Japanese infants develop the perceptual sensitivity for native phonotactics after 6 months of age, and that this sensitivity is limited to canonical patterns at this early developmental stage.