Stereoselective synthesis of alpha-C-glucosyl serine and alanine via a cross-metathesis/cyclization strategy

C-Glycosyl amino acids represent stable mimics of monomeric units within natural O-linked glycoproteins. Olefin cross-metathesis has been used to provide alkene precursors for a mercury(II)-mediated cyclization, yielding alpha-C-glucosyl serine and alanine.     

Stability of Generalized Transition Fronts

We study the qualitative properties of the generalized transition fronts for the reaction–diffusion equations with the spatially inhomogeneous nonlinearity of the ignition type. We show that transition fronts are unique up to translation in time and are globally exponentially stable for the solutions of the Cauchy problem. The results hold for reaction rates that have arbitrary spatial variations provided that the rate is uniformly positive and bounded from above.     

Syntheses of alpha- and beta-C-glucopyranosyl serines from a common intermediate

A versatile synthesis leading to either C-linked alpha- or beta-glucopyranosyl serines is presented from a common, advanced synthetic intermediate. Cyclization of the penultimate carbinol onto the alkene and methanolysis of the lactone yields selectively the alpha-linkage. A transposition of these last steps leads to the beta-linked isomer selectively.     

Synthesis of C-linked glycopyranosyl serines via a chiral glycine enolate equivalent

[formula: see text] The stereoselective preparation of C-linked D-gluco- and D-galactopyranosyl L-serines in their alpha and beta forms is herein reported. The syntheses require the conversion of the allyl C-glycopyranosides into their iodoethyl derivatives, which then undergo substitution with the Williams' chiral glycine enolate equivalent. Deprotection and acetylation affords Boc-protected amino acids for peptide synthesis.     

Synthesis of Orthogonally Protected S,S-2,6-Diaminopimelic Acid via Olefin Cross-Metathesis

A short synthesis of orthogonally protected S,S-diaminopimelic acid, DAP, via a selective cross-metathesis between S-allyl glycine and S-vinyl glycine followed by hydrogenation is reported. By analogy, the S,S-diaminosuberic acid, DAS, is produced by self-metathesis of S-allyl glycine, and the self-metathesis of S-vinyl glycine is described.     

Computing reactive front speeds in random flows by variational principle

We study reactive front speeds in randomly perturbed cellular flows using a variational representation for the front speed. We develop this representation into a computational tool for computing the front speeds without resorting to closure approximations. We demonstrate that the front speeds depend on flow statistics and topologies in a complex and dramatic manner.     

Combined chromatographic-isotopic dilution analysis of fecapentaenes in human feces

Fecapentaene-12 (FP-12) and fecapentaene-14 (FP-14) are genotoxic unsaturated ether lipids produced by colonic bacteria in man. We have developed and applied to feces collections from normal volunteers direct isotopic dilution procedures using tritium-labeled (at C5) FP-12 and FP-14 for measuring these compounds. FPs were recovered from feces by solvent extraction, silica cartridge clean-up, and analytical liquid chromatography. Low levels of FP-12 and FP-14 (less than 0.1 to 2.4 micrograms/g of freeze-dried feces) were observed. Identity of chromatographic peaks was established by co-elution and by ultraviolet absorption spectra obtained via photodiode array scanning. Two unknown peaks were tentatively identified from absorption spectra as closely related compounds with increased (hexane?) or decreased (tetraene?) number of double bonds. Levels of FPs increased after incubation of feces at 37 degrees C for 96 h under anaerobic conditions and pre-FP-12 and pre-FP-14 peaks were observed, which showed identical spectra with authentic FPs. These were interpreted to be isomeric forms of the all-trans-[3H]FPs used for the isotopic dilution analysis. Total FPs (including pre-FP) yielded a range of 0.3-80 micrograms FP-12 and 2.8-44 micrograms FP-14 per g of freeze-dried feces from the study group.