The advantages of stable glycosyl donors for saccharide coupling are many, and we describe herein the utility of propargyl glycosides for anomeric activation and glycoside synthesis exploiting the alkynophilicity of AuCl3. Various aglycones were reacted with propargyl glycosides, resulting in the formation of an alpha,beta-mixture of glycosides and disaccharides in good yields.
An unprecedented visible-light inspired selective radical azidation of unactivated and diverse substituted vinylarenes with sulfonium iodate reagent has been realized. The intrinsic radical process triggered by light tolerated several synthetically useful functionalities enabling two new carbon-hetero bonds which display distinctive late-stage applications to biologically relevant scaffolds.
Photoresponsive gold nanoparticle networks were prepared by functionalizing them with azobenzene derivatives. A network can be formed when a linker molecule constituting the azobenzene moiety suitably derivatized on either side with gold surface sensitive groups such as thiols and amines is added to the nanoparticle solution. It is shown that the interparticle spacing in the networks could be controlled by the reversible trans-cis isomerization of the azobenzene moiety induced by UV and visible light, respectively. The photoinduced variation in the interparticle spacings is inferred by the changes in the optical spectra of the gold nanoparticles which display a red or blue shift in the surface plasmon resonance peak depending on a decrease or increase in the interparticle spacing, respectively. Transmission electron microscopy images are in consonance with the evidence from the optical spectra.
[reaction: see text] Various pseudo-oligosacchardies and amino acid glycoconjugates were synthesized via an intermolecular 1,3-dipolar cycloaddition ("click") reaction using easily accessible carbohydrate and amino acid derived azides and alkynes as building blocks. It is pertinent to mention that the conjugation reaction is highly regioselective and high yielding and can be carried out under mild reaction conditions.
We acknowledge that Drs. Zoe Pikramenou and Peter Glover (University of Birmingham) first prepared and provided a sample of the nonfluorinated Er(tpip) 3 compound for initial studies, though none of the work detailed in this paper has utilized that sample. Table 1 should read as follows: a Obtained with graphite-monochromated Mo KR (λ ) 0.71073 Å) radiation for 1, 3, 4, and 5, and synchrotron radiation (λ ) 0.775 Å) for 2 and 6. Supporting Information Available: An incorrect spatial correction file was used for the X-ray detector at the Advanced Light Source of Lawrence Berkeley National Laboratory. This caused systematic errors in the lattice parameters and peak prediction and resulted in poor integration and loss of highangle data for compounds 2 and 6. A reintegration of the X-ray diffraction data for these compounds using the correct spatial correction file provided a more precise refinement of the crystal structures. Updated CIF files have therefore been submitted for compounds 2 and 6. This material is available free of charge via the Internet at http://pubs.acs.org. We have now found that the transglycosylation reaction we described does not proceed in the presence of organic bases such as triethyl amine and diisopropylethyl amine. Furthermore, propargyl glycosides do not behave as glycosyl donors in dioxane‚HCl or Et 2 O‚HCl. Interestingly, the transglycosylation reaction between the propargyl per-O-benzylated glucoside (4a) and menthol (6a) proceeded with 5 mol % of HAuCl 4 in acetonitrile at 60°C, giving 45% of lactol 5a and 30% of menthyl glucoside 5b.The authors thank the reader who suggested these experiments.
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