Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates

An efficient direct one-pot glycosylation method with anomeric hydroxy sugars as glycosyl donors employing phthalic anhydride and triflic anhydride as activating agents has been developed. Thus, highly stereoselective beta-mannopyranosylations were achieved by the reaction of 2,3-di-O-benzyl-4,6-O-benzylidene-D-mannopyranose (2) with phthalic anhydride in the presence of DBU at room temperature followed by sequential addition of DTBMP and Tf2O and glycosyl acceptors to the reaction mixture at -78 degrees C in one-pot. Stereoselective alpha-glucopyranosylations with 2,3-di-O-benzyl-4,6-O-benzylidene-D-glucopyranose (25) and other glycosylations with glucopyranoses and mannopyranoses having tetra-O-benzyl- and tetra-O-benzoyl protecting groups were also possible by utilizing the present one-pot glycosylation protocol. The possible mechanism for the beta-mannosylation with 2 was proposed based on the NMR study, in which alpha-mannosyl phthalate 55alpha and alpha-mannosyl triflate 59 were detected as intermediates. The versatility and efficiency of the present glycosylation methodology, especially those of the beta-mannopyranosylation protocol, were readily demonstrated by the efficient synthesis of protected beta-(1-->4)-D-mannotriose 62 and beta-(1-->4)-D-mannotetraose 67 with perfect beta-stereoselectivity.     

Cyclic diarylheptanoids inhibit cell-mediated low-density lipoprotein oxidation

Two cyclic diarylheptanoids, garugamblin-3 (1) and acerogenin L (2), isolated from the MeOH extract of the fruits of Alnus japonica Steud., inhibited human low-density lipoprotein (LDL) oxidation in the thiobarbituric acid-reactive substance assay with IC50 values of 2.9 and 1.7 microM, respectively, and they also inhibited cell-mediated LDL oxidation more than five times more strongly than that of a well-known antioxidant, probucol, at a concentration of 10 microM. 1 had no effect on the anti-atherogenesis in low-density lipoprotein receptor- deficient mice.     

Modification of both the electrophilic center and substituents on the nonleaving group in pyridinolysis of O-4-nitrophenyl benzoate and thionobenzoates

A kinetic study is reported for reactions of 4-nitrophenyl benzoate (1c) and O-4-nitrophenyl X-substituted thionobenzoates (2a-e) with a series of pyridines in 80 mol % H2O/20 mol % dimethyl sulfoxide (DMSO) at 25.0 +/- 0.1 degrees C. O-4-Nitrophenyl thionobenzoate (2c) is more reactive than its oxygen analogue 1c toward all the pyridines studied. The Br?nsted-type plot is linear with beta(nuc)=1.06 for reactions of 1c but curved for the corresponding reactions of 2c with beta(nu)c decreasing from 1.38 to 0.38 as the pyridine basicity increases, indicating that the reaction mechanism is also influenced on changing the electrophilic center from C=O to C=S. The curvature center of the curved Br?nsted-type plots (defined as pK(a)(o)) occurs at pKa = 9.3 regardless of the electronic nature of the substituent X in the nonleaving group. The Hammett plot for reactions of 2a-e with 4-aminopyridine is nonlinear, i.e., the substrates having an electron-donating substituent exhibit negative deviations from the Hammett plot. However, the Yukawa-Tsuno plot for the same reactions exhibits good linear correlation, indicating that the negative deviations shown by these substrates arise from stabilization of the ground state through resonance interaction between the electron-donating substituent X and the C=S bond.     

A Multifunctional Subphthalocyanine Nanosphere for Targeting,Labeling, and Killing of Antibiotic‐Resistant Bacteria

Developing a material that can combat antibiotic‐resistant bacteria, a major global health threat, is an urgent requirement. To tackle this challenge, we synthesized a multifunctional subphthalocyanine (SubPc) polymer nanosphere that has the ability to target, label, and photoinactivate antibiotic‐resistant bacteria in a single treatment with more than 99 % efficiency, even with a dose as low as 4.2 J cm⁻² and a loading concentration of 10 nM . The positively charged nanosphere shell composed of covalently linked SubPc units can increase the local concentration of photosensitizers at therapeutic sites. The nanosphere shows superior performance compared to corresponding monomers presumably because of their enhanced water dispersibility, higher efficiency of singlet‐oxygen generation, and phototoxicity. In addition, this material is useful in fluorescence labeling of living cells and shows promise in photoacoustic imaging of bacteria in vivo.     

Highly Stable,Water‐Dispersible Metal‐Nanoparticle‐Decorated Polymer Nanocapsules and Their Catalytic Applications

A facile synthesis of highly stable, water‐dispersible metal‐nanoparticle‐decorated polymer nanocapsules (M@CB‐PNs: M=Pd, Au, and Pt) was achieved by a simple two‐step process employing a polymer nanocapsule (CB‐PN) made of cucurbit[6]uril (CB[6]) and metal salts. The CB‐PN serves as a versatile platform where various metal nanoparticles with a controlled size can be introduced on the surface and stabilized to prepare new water‐dispersible nanostructures useful for many applications. The Pd nanoparticles on CB‐PN exhibit high stability and dispersibility in water as well as excellent catalytic activity and recyclability in carbon–carbon and carbon–nitrogen bond‐forming reactions in aqueous medium suggesting potential applications as a green catalyst.     

Iron‐catalyzed living radical polymerization of acrylates: Iodide‐based initiating systems and block and random copolymerizations

A half‐metallocene iron iodide complex [Fe(Cp)I(CO)₂] induced living radical polymerization of methyl acrylate (MA) in conjunction with an iodide initiator [(CH₃)₂C(CO₂Et)I, 1 ] and Al(Oi‐Pr)₃ to give polymers of controlled molecular weights and narrow molecular weight distributions (MWDs) (M_w/M_n < 1.2). With the use of chloride and bromide initiators, the MWDs were broader, whereas the molecular weights were similarly controlled. Other acrylates such as n‐butyl acrylate (nBA) and tert‐butyl acrylate (tBA) can be polymerized with 1 /Fe(Cp)I(CO)₂ in the presence of Ti(Oi‐Pr)₄ and Al(Oi‐Pr)₃, respectively, to give living polymers. The 1 /Fe(Cp)I(CO)₂ initiating system is applicable for the synthesis of block and random copolymers of acrylates (MA, nBA, and tBA) and styrene of controlled molecular weights and narrow MWDs (M_w/M_n = 1.2–1.3). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2033–2043, 2002     

Direct glycosylation with anomeric hydroxy sugars by activation with 3-fluorophthalic anhydride and trifluoromethanesulfonic anhydride

An efficient and direct one-pot glycosylation method using anomeric hydroxy sugars as glycosyl donors, employing 3-fluorophthalic anhydride and triflic anhydride as activating agents, has been developed. The present glycosylation utilizing 3-fluorophthalic anhydride resulted in few to no undesired self-condensed esters than the glycosylation using phthalic anhydride. Intermediates in the present glycosylation were identified by an NMR study.