Preparation of 9,13-dicis double bonds locked retinoids

Synthesis of two retionids in which the 9, 13-dicis double bonds were locked in cycloalkene or thiophene was described. The key steps were the Wittig olefination of phosphonium salt 3 and 23 with aldehyde 14, followed by carbonylation of vinyl bromide 17 and 24 with carbon monoxide in the presence ofPd(PPh3)4.     

Diverse synthesis of the C ring fragment of bryostatins via Zn/Cu-promoted conjugate addition of α-hydroxy iodide with enone

A convergent approach to 1,5-hydroxy ketones,the general precursors for constructing the C ring of bryostatins,has been developed via a Zn/Cu-promoted conjugate addition of a-hydroxy iodides with enones.The reaction leads to direct formation of the C21-C22 bond and tolerates diverse functionalities at the C17-,C18-and C24-positions.The approach also enables a more concise synthesis of the known C ring intermediate(10 longest linear steps and 14 total steps),in contrast to its previous synthesis(17 longest linear steps and 22 total steps) in our total synthesis of bryostatin 8.     

Regioselective protection of 10-deacetylbaccatin Ⅲ and semi-synthesis of paclitaxel

Semi-synthesis of paclitaxel was achieved in four steps from 10-deacetylbaccatin HI （10-DAB HI）. The key steps are the regioselective protection at the hydroxyl group at C-7 of 10-DAB HI, using 1,1′-thiocarbonyldiimidazole as a selective reagent, and the deprotection of the protected paclitaxel with a mixture of p-toluenesulfonic acid and 0.1 mol/L aqueous hydrochloride.     

Total synthesis and biological evaluation of dracaenins A and B

The first total synthesis of dracaenins A and B is achieved in four steps. The synthesis features the convergent coupling of three readily available fragments with minimized use of protecting groups. The chemical synthesis enables the discovery of their activity in stimulating platelet aggregation, and thus, sheds light on the possible origin of the hemostatic effect of dragon’s blood.     

Density Functional Study on the Reaction Mechanism for the Reaction of Ni^＋ with Ethane

The mechanism of the reaction of Ni^ (^2D) with ethane in the gas-phase was studied by using density functional theory.Both the B3LYP and BLYP functionals with standard all-electron basis sets are used to give the detailed information of the potential energy surface (PES) of [Ni,C2,H6]^ . The mechanisms forming the products CH4 and H2 in the reaction of Ni^ with ethane are proposed.The reductive eliminations of CH4 and H2 are typical addition-elimination reactions.Each of the two reactions consists of two elementary steps:C-C or C-H bond activations to form inserted species followed by isomerizations to from product-like intermediate.The rate determining steps for the elimination reactions of forming CH4 and H2 are the isomerization of the inserted species rather than C-C or C-H bond activations .The elimination reaction of forming H2 was found to be thermodynamically favored compared to that of CH4.     

Total Synthesis of (±) Euphraticol and Its Analogues

Total syntheses of racemic Euphraticol and its analogues are described, they constitute anew and efficient synthetic route to abietane diterpenoids. The key steps are alkylation of lithium eno-late of 8 with iodides in the presence of HMPA.     

First Synthesis of a Series of New Natural Glucosides

Alkyl glucoside 1 and aryl glycosides 2-4 were highly stereospecifically synthesized over 4-6 steps from commercially available starting materials. The coupling reaction of the acetobromo-α-D-glucose with the unprotective dihydroxy aglycon in the presence of silver oxide, or with aromatic aglycon in the presence of sodium hydroxide produced the key intermediate. Only β-configuration glycosides were formed in this procedure. The synthesis of all these glycosides was reported for the first time.     

OBSERVATION OF A COMPETITIVE PATH IN THE NUCLEOPHILIC ADDITION REACTION OF FLUOROOLEFINS:THE BROMOPHILIC REACTION OF THE ADDUCT CARBANION INTERMEDIATE

The nucleophilic addition reaction of per-or polyfluoroolefins with nucleophileshas been studied extensively and is generally considered to involve steps such as(1),(2)and(3)shown in Scheme 1.But in the reactions of bromotrifluoroethene(3)with alkoxides RO~-(2),besides the normally expected products ROCF_2CFBrH(4)     

Quick pH-responsive Films Prepared from Urethane Acrylate Anionomers Under UV Radiation and Their Responsive Performances

Urethane acrylate anionomers(UAA) were prepared in various compositions by three steps. Under UV radiation, UAA formed pH-sensitive films with drying film thicknesses of 60,200 and 330 ttm. The equilibrium swelling ratios(SR) of the films in various pH buffer solutions increased with the increase of the molecule weight of UAA. The influence of the film thicknesses on the swelling performances of the films was investigated. The film with a thickness of 60μm could reach the equilibrium state in 2.5--3.5 min. A high SR was obtained for a thick film due to its low average network density. The cured film could swell reversibly and rapidly with the change of pH, which is important for a controlled release system.     

A STUDY OF ELECTROCHEMICAL REDUCTION OF SAFRANINE T AND THE ELECTROGENERATED FREE RADICAL TRACING BY ESR

A study of the electrochemical reduction behavior of safranine T by means of electrochemical methods coupled with ESR (electron spin resonance) is presented. Through an "in situ" tracing of the 1-electron reduction intermediate—free radical, the structure of the free radical has been deduced. During the electrochemical reduction the free radical went through a post-electrolysis chemical decay including parallel steps of zero and first order reactions. This fact gives further support and experimental ascertainment of the viewpoint that some electrode processes are clearly related to the enzymatic catalyses~([1]). In accordance with the chemical behavior of safranine T free radicals at various concentrations and at different potentials the authors have advanced a scheme of reaction mechanism and evaluated the kinetic parameters of the reation steps by simulating the experimental curves.     

Enzymatic Synthesis of a CCK-8 Tripeptide Derivative

The enzymatic synthesis of CCK-8 tripeptide derivative Phae-Met-Asp(OMe)-Phe-NH2 is reported.Starting with Phac-Met-OCam,we have successfully synthesized the target tripeptide with three free or immobilized enzymes, α-chymotrypsin,papain and thermolysin in reasonable yields.The key steps in this synthesis were the coupling of Phac-Met-OCam and H-Asp(OMe)2 to from Met-Asp peptide bond catalyzed by α-chymotrypsin and the selective hydrolysis of α-ester of Phac-met-Asp(OMe)2 catalyzed by papain.     

Access to chiral homoallylic vicinal diols from carbonyl allylation of aldehydes with allyl ethers via palladium-catalyzed allylic C-H borylation

Chiral homoallylic vicinal diols are found in many bioactive compounds and are among the most versatile functional groups in organic chemistry. Here, we describe an asymmetric carbonyl allylation of aldehydes with allyl ethers proceeding via allylic C-H borylation enabled by palladium and chiral phosphoric acid sequential catalysis, providing facile access to homoallylic vicinal anti-diols in high yields and with excellent stereoselectivity. This protocol enables the total synthesis of aigialomycin D to be finished within 7 steps.     

SNAP-tag fluorogenic probes for wash free protein labeling

In this review, we described the design strategies of SNAP-tag fl uorogenic probes with turn-on fl uorescence responses, which minimized the fl uorescence background and allowed for direct imaging in living cells without wash-out steps. These probes can apply in real-time analysis of protein localization, dynamics, and protein– protein interactions in living cells. Furthermore, the excellent fl uorescent properties made it possible to apply some of the probes in super-resolution fl uorescence imaging.     

Metal and organo-catalysed asymmetric hydroaminomethylation of styrenes

A new protocol that enables asymmetric hydroaminomethylation of styrenes to afford chiral amines has been developed. Catalysed by an Rh-phosphine species and a chiral phosphoric acid, styrenes are converted into β-chiral amines with good enantioselectivities under syngas in the presence of an amine and Hantzsch ester. The reaction involves two key steps, hydroformylation and reductive amination, with the former catalysed by the Rh species whilst the latter by the phosphoric acid.     

Polymeric bilayer modified microelectrodes for in-vivo determination of neurotransmitter dopamine

A composite polymer carbon fiber electrode modified with Nafion and cellulose acetate is described.The modified electrode discriminates against both anionic reactants and big molecular organic compounds.The bilayer configuration is prepared in two steps.First,the carbon fiber electrode is coated with Nafion,then followed by air evaporation of the solvent,the electrode is dipped in a cellulose acetate solution and hydrolyzed for a selected time.The permeability of the film is explored by use of rotating disk electrode measurements.Parameters affecting the film electrochemistry are investigated.The resulting electrodes show high selectivity and stability in body fluids.For in-vivo voltammetry,the composite polymer modified electrode has been used for detection of the oxidative current of neurotransmitter dopamine in rat brain,while it inhabits the oxidation of anionic neurotransmitter metabolites and some electroactive compounds.     

A simple and efficient synthesis of the valsartan

Valsartan 1, one of the most important agents used in antihypertensive therapy today, was synthesized starting from L-valin methyl ester hydrochloride 2 through four steps in an overall yield of 60%. The key step involves the palladium-catalyzed Suzuki coupling. This method overcomes many of the drawbacks associated with the previously reported syntheses and is more suitable for industrial production.     

THE STUDY OF THE REACTION OF THE QUASI-AROMATIC COMPLEX [Ni(PnAO)-6H]~(?)WITH FORMALDEHYDE: KINETICS AND MECHANISM

The kinetics of the reaction of [Ni(PnAO)—6H]° with formaldehyde was studied in H_2O—CH_3OH solution under neutral condition and a complicated mechanism with three steps including competitive, consecutive and reverse reactions was proposed.     

STUDIES ON STEROIDAL PLANT-GROWTH REGULATORS (ⅩⅦ)——A NEW SYNTHESIS OF HOMOBRASSINOLIDE AND (22S,23S)-22,23-EPI-HOMOBRASSINOLIDE

Homobrassinolide (2) and (22S, 23S)-22,23-epi-homobrassinolide (4) were synthesized fromstigmasterol in seven steps respectively in 4.7% and 24.1% overall yields. The ratio of 2 to 4is 1:5. The key step is the highly regioselective formation of the B--homo-7-oxa-lactone ringby oxidation of an enol silyl ether with 3--chloro-peroxybenzoic acid.     

AN ESR STUDY OF ELECTROCHEMICAL REDUCTION OF NITROBENZENE

By means of a highly sensitive electrolytic cell installed in the ESR cavity, the authors investi-gated in situ the kinetic behavior of the primary electroreduction product (a radical anion) in a sol-vent mixture of water and ethanol over a wide range of pH. For the first time they observed somefurther complex kinetic behaviors of the electroreduction process of nitrobenzene. Through a study ofthe behavior of the radical anion (φ-NO_2~-.) with variations of pH, concentration of nitrobenzene(φ-NO_2) and electroreduction potential, they advanced a reaction scheme of the electroreduction ofnitrobenzene and simulated the experimental curves in order to evaluate the kinetic parameters of thereaction steps concerned.     

A Convenient Synthesis of Chrysin and Tectochrysin

Chrysin(1) and tectochrysin(2) were respectively synthesized in four steps from 1,3,5-tribromobenzene in an overall yield of 46.8％ and that of 37.0％ with the key step being the Bu_4NBr catalyzed hydrolysis of 1-phenyl-3-(2′,4′,6′-trimethoxyphenyl)-1, 3-propanedione (11) under different conditions.