Highly efficient Suzuki-Miyaura coupling reactions catalyzed by bis(oxazolinyl)phenyl-Pd(II) complex

Bis(oxazolinyl)phenyl-palladium(II)(Phebox-Pd) complexes were found to be efficient catalysts for Suzuki-Miyaura coupling reactions of aryl boronic acids and their derivatives with aryl halides to give the corresponding biaryl products in high yield along with moderate enantioslectivities in the case of axially chiral induction. The catalytic activity was attained more than 900,000 of TON and 45,000 of TOF. The catalyst can be recovered quantitatively and could be reused for Suzuki-Miyaura reactions.     

Synthesis of beta-substituted alpha-amino acids with use of iridium-catalyzed asymmetric allylic substitution

The asymmetric synthesis of beta-substituted alpha-amino acids with use of iridium-catalyzed allylic substitution was described. The Ir-catalyzed allylic substitution of diphenylimino glycinate with allylic phosphates proceeded smoothly even at 0 degrees C and gave branch products with high enantioselectivity (up to 97% ee), when chiral bidentate phosphite bearing the 2-ethylthioethyl group was employed. In addition, both diastereomers of the branch products were synthesized stereoselectively by simply switching the base employed. These methods were also applied to the asymmetric synthesis of quaternary alpha-amino acids.     

Hydroxylamines as oxygen atom nucleophiles in transition-metal-catalyzed allylic substitution

[reaction: see text] The viability of hydroxylamines as nucleophiles in transition-metal-catalyzed allylic substitutions was examined. We have found that the oxygen atom of hydroxylamines having an N-electron-withdrawing substituent (also known as hydroxamic acids) acts as a reactive nucleophile. The palladium-catalyzed O-allylic substitution of hydroxylamines with allylic carbonate afforded the linear hydroxylamines. The selective formation of the branched hydroxylamines was observed in iridium-catalyzed reaction. Regio- and enantioselective allylic substitution of the unsymmetrical phosphates with hydroxylamines was studied by using the iridium complex of chiral pybox ligand. The aqueous-medium reaction with hydroxylamines proceeded smoothly in the presence of Ba(OH)(2).H(2)O to give the branched products with good enantioselectivities.     

Application of the synthetic aminosugars for glycodiversification: synthesis and antimicrobial studies of pyranmycin

A divergent approach was employed for the synthesis of aminosugars, from which a novel library of aminoglycoside antibiotics (pyranmycins) was synthesized. Pyranmycins have comparable antibacterial activity as neomycin, a clinically used aminoglycoside antibiotic, against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Mycobacterium smegmatis. In addition, pyranmycins, like streptomycin, are bacteriocidal while isoniazid (INH) is bacteriostatic. Therefore, pyranmycins may provide new therapeutic options in the treatment against tuberculosis. Several members of pyranmycins also manifest modest anti-Tat and anti-Rev activities, which may aid in the development of new anti-HIV agents. Although the antibacterial activity of pyranmycins against aminoglycoside resistant bacteria is less than expected, the synthetic methodologies of utilizing a library of aminosugars can be a model for future studies of glycodiversification or glycorandomization.     

Indium-mediated tandem radical addition-cyclization-trap reactions in aqueous media

[reaction: see text] Tandem carbon-carbon bond-forming reactions were studied by using indium as a single-electron-transfer radical initiator. The radical addition-cyclization-trap reaction of a substrate having a vinyl sulfonamide group and an olefin moiety proceeded smoothly in aqueous media. The radical addition-cyclization reaction of hydrazone gave the functionalized cyclic products.     

Inokosterone, an insect metamorphosing substance from Achyranthes fauriei : Absolute configuration and synthesis

Inokosterone, a phytoecdysone isolated from Achyranthes fauriei (Amaranthaceae), has been partially acetylated to give the 2,26-diacetate (4) which has been converted into methyl 5 - acetoxy - 4 - methylpentanoate (7), showing no apparent []_D, and 2β - acetoxy - 3β,14 - dihydroxy - 5β - pregn - 7 - ene - 6,20 - dione (8). Chemical and physiochemical studies have shown the configurations at C-20 and C-22 to be R. Inokosterone has thus been concluded to be a mixture of C-25 epimers of (20R,22R) - 2β,3β,14,20,22,26 - hexahydroxy - 5β - cholest - 7 - en - 6 - one (1). After the synthesis of the model compound, a C-25 epimeric mixture of (20R,22R) - 3β,20,22,26 - tetrahydroxy - 5 - cholestane (23), inokosterone has been synthesized via (20R) - 2β,3β,14,20 - tetrahydroxy - 20 - formyl - 5β - pregn - 7 - en - 6 - one (25) by Grignard reaction with 4 - (tetrahydrofuran - 2 - yloxy) - 3 - methylbutynylmagnesium bromide (15) followed by hydrogenation and hydrolysis. The use of an NMR shift reagent with the inokosterone acetates (9, 29) and the optical activity measurement of - methylglutaric acid (3) derived from inokosterone have established that inokosterone is a 1:2 mixture of the C-25 R and S epimers.     

Functional monomers and polymers. CVIII. Photodimerization of pendant thymine bases in thymine containing poly-lysine derivatives

The photodimerization reaction of pendant thymine bases in thymine-containing poly-lysine derivatives was studied over a wide range in aqueous solution. It was found that the quantum yield of the photodimerization of pendant thymine bases is affected mainly by the conformation of the polymers in solution. The differences in photoreaction behavior were discussed for poly-D -, poly-L -, and poly-DL -lysine derivatives.     

Membrane-permeabilizing activities of cyclic lipodepsipeptides, syringopeptin 22A and syringomycin E from Pseudomonas syringae pv. syringae in human red blood cells and in bilayer lipid membranes

The pore-forming activities of cyclic lipodepsipeptides (CLPs), syringopeptin 22A (SP22A) and syringomycin E (SRE) were compared on the human red blood cell (RBC) membrane and on bilayer lipid membranes (BLMs). SP22A above a concentration of 4 x 10(5) molecules/cell significantly increased the RBC membrane permeability for 86Rb. With electric current measurements on BLM, it was proved that like SRE, the SP22A formed two types of ion channels in the membrane, small and large, the latter having six times larger conductance and longer dwell time. Both CLPs formed clusters consisting of six small channels, and the channel-forming activity of SP22A is about one order of magnitude higher than that of SRE. A Hill coefficient of 2-3 estimated from the concentration dependence of these CLPs-induced lysis gave a proof of the pore oligomerization on RBCs. Transport kinetic data also confirmed that SP22A pores were oligomers of at least three monomers. While SRE pores were inactivated in time, no pore inactivation was observed with SP22A. The 86Rb efflux through SP22A-treated RBCs approached the tracer equilibrium distribution with a constant rate; a constant integral current was measured on the BLM for as long as 2.5 h as well. The partition coefficient (Kp = 2 x 10(4) l/mol) between the RBC membrane and the extracellular space was estimated for SRE to be at least six times higher than that for SP22A. This finding suggested that the higher ion permeability of the SP22A-treated cells compared to that of SRE was the result of the higher pore-forming activity of SP22A.     

Six new triterpenoidal glycosides including two new sapogenols from Albizziae Cortex. V.

Six new triterpenoid glycosides called julibrosides A1-A4, B1 and C1 were isolated from Albizziae Cortex, the dried stem bark of Albizzia julibrissin Durazz. Their structures were determined based on spectral and chemical evidence. Julibrosides B1 and C1 had new sapogenols, designated julibrogenin B and C, respectively, while julibrosides A3 included N-acetyl-D-glucosamine as a sugar component.     

包结聚合

本文主要叙述以脱胆酸(DCA)为包结体的包结聚合的研究历史。各种烯类单体、双烯、环状双烯、双炔、氯代丙烯腈等聚合单体在DCA管道中的包结聚合行为及不对称包结聚合。