Enantioselective Synthesis in Continuous Flow: Polymer-Supported Isothiourea-Catalyzed Enantioselective Michael Addition-Cyclization with α-Azol-2-ylacetophenones.

A packed reactor bed incorporating a polymer-supported isothiourea HyperBTM catalyst derivative has been used to promote the enantioselective synthesis of a range of heterocyclic products derived from α-azol-2-ylacetophenones and -acetamides combined with alkyl, aryl, and heterocyclic α,ß-unsaturated homoanhydrides in continuous flow via an α,ß-unsaturated acyl-ammonium intermediate. The products are generated in good to excellent yields and generally in excellent enantiopurity (up to 97:3 er). Scale-up is demonstrated on a 15 mmol scale, giving the heterocyclic product in 68% overall yield with 98:2 er after recrystallization.

Understanding divergent substrate stereoselectivity in the isothiourea-catalysed conjugate addition of cyclic α-substituted ß-ketoesters to α,ß-unsaturated aryl esters.

The development of enantioselective synthetic methods capable of generating vicinal stereogenic centres, where one is tetrasubstituted (such as either an all-carbon quaternary centre or where one or more substituents are heteroatoms), is a recognised synthetic challenge. Herein, the enantioselective conjugate addition of a range of carbo- and heterocyclic α-substituted ß-ketoesters to α,ß-unsaturated aryl esters using the isothiourea HyperBTM as a Lewis base catalyst is demonstrated. Notably, divergent diastereoselectivity is observed through the use of either cyclopentanone-derived or indanone-derived substituted ß-ketoesters with both generating the desired stereodefined products with high selectivity (>95 : 5 dr, up to 99 : 1 er). The scope and limitations of these processes are demonstrated, alongside application on gram scale. The origin of the divergent substrate selectivity has been probed through the use of DFT-analysis, with preferential orientation driven by dual stabilising CH⋯O interactions. The importance of solvation with strongly polar transition-states is highlighted and the SMD solvation model is demonstrated to capture solvation effects reliably.

Lewis acid-catalyzed asymmetric reactions of ß,γ-unsaturated 2-acyl imidazoles.

The investigation of diverse reactivity of ß,γ-unsaturated carbonyl compounds is of great value in asymmetric catalytic synthesis. Numerous enantioselective transformations have been well developed with ß,γ-unsaturated carbonyl compounds as nucleophiles, however, few example were realized by utilizing them as not only nucleophiles but also electrophiles under a same catalytic system. Here we report a regioselective catalytic asymmetric tandem isomerization/α-Michael addition of ß,γ-unsaturated 2-acyl imidazoles in the presence of chiral N,N'-dioxide metal complexes, delivering a broad range of optically pure 1,5-dicarbonyl compounds with two vicinal tertiary carbon stereocenters in up to >99% ee under mild conditions. Meanwhile, stereodivergent synthesis is disclosed to yield all four stereoisomers of products. Control experiments suggest an isomerization process involved in the reaction and give an insight into the role of NEt3. In addition, Mannich reaction and sulfur-Michael addition of ß,γ-unsaturated 2-acyl imidazoles proceed smoothly as well under the same catalytic system.

Enantioselective Imino-Ene Reaction of N-Sulfonyl Ketimines with Silyl Enol Ethers: Access to Chiral Benzosultams.

A highly efficient asymmetric imino-ene reaction of cyclic ketimines with silyl enol ethers was developed. Various chiral benzosultam derivatives were obtained in excellent yields (up to 99%), enantioselectivities (up to 99% ee), and diastereoselectivities (up to >19:1 dr) by utilizing a Ni(BF4)2·6H2O/N,N'-dioxide complex as the catalyst. A possible transition state model was proposed to explain the stereoinduction. Furthermore, the synthetic utility of the protocol provided quick access to optically pure HIV-1 inhibitor.

Organocatalytic Asymmetric Michael/Dieckmann Cyclization Reaction of Alkynones To Construct Spirocyclopentene Oxindoles.

A highly enantioselective conjugate addition/Dieckmann cyclization of 3-carboxymethyl substituted oxindoles with electron-deficient internal alkynes was achieved under the catalysis of a chiral guanidine catalyst and NaH. This protocol provides access to a wide range of synthetically useful optically active spirocyclopentenone oxindoles and their derivatives under mild reaction conditions.

Bimetallic Catalytic Asymmetric Tandem Reaction of ß-Alkynyl Ketones to Synthesize 6,6-Spiroketals.

The enantioselective tandem reaction of ß,γ-unsaturated α-ketoesters with ß-alkynyl ketones was realized by a bimetallic catalytic system of achiral AuΙΙΙ salt and chiral N,N'-dioxide-MgΙΙ complex. The cycloisomerization of ß-alkynyl ketone and asymmetric intermolecular [4+2] cycloaddition with ß,γ-unsaturated α-ketoesters subsequently occurred, providing an efficient and straightforward access to chiral multifunctional 6,6-spiroketals in up to 97 % yield, 94 % ee and >19/1 d.r. Besides, a catalytic cycle was proposed based on the results of control experiments.

Chiral Zinc(II)-Catalyzed Enantioselective Tandem α-Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines.

A new catalytic asymmetric tandem α-alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N'-dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α-alkenyl addition of silyl enol ether to the ketimine. A wide range of ß-amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama-Mannich reaction and tandem α-alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained ß-amino silyl enol ethers were easily transformed into ß-fluoroamines containing two vicinal tetrasubstituted carbon centers.

Asymmetric Catalytic Double Michael Additions for the Synthesis of Spirooxindoles.

Asymmetric cascade double Michael additions to construct 2'-substituted 3,3'-spirooxindoles by using a chiral guanidine organocatalyst has been developed. A series of spirooxindole derivatives containing dihydrofuran or pyrrolidine subunits were obtained with good to excellent diastereo- and enantioselectivities. The method showed great tolerance of a number of aromatic and aliphatic alkynones. The strategy gave access to the asymmetric synthesis of (-)-salacin for the first time.

Chiral N,N'-dioxide/Sc(OTf)3 complex-catalyzed asymmetric dearomatization of ß-naphthols.

An efficient N,N'-dioxide-scandium(iii) complex catalytic system has been developed for the asymmetric dearomatization of ß-naphthols through conjugate addition to alkynones. A variety of Z-predominated ß-naphthalenone compounds were obtained in moderate to high yields with excellent enantioselectivities (up to 98% ee). Moreover, a possible transition state was proposed to explain the origin of the stereoselectivity.

Catalytic asymmetric [2+2] cycloaddition between quinones and fulvenes and a subsequent stereoselective isomerization to 2,3-dihydrobenzofurans.

The catalytic enantioselective [2+2] cycloaddition between quinones and fulvenes was achieved, for the first time, by the use of a chiral copper(ii) complex catalyst. The transformation afforded a series of enantiomerically enriched [6,4,5]-tricyclic cyclobutane derivatives in good yields with excellent regio- and stereoselectivities. Furthermore, the [2+2] adducts could be easily converted into formal [3+2] adducts efficiently and stereoselectively.

A Chiral N,N'-Dioxide-Zn(II) Complex Catalyzes the Enantioselective [2+2] Cycloaddition of Alkynones with Cyclic Enol Silyl Ethers.

A highly efficient enantioselective [2+2] cycloaddition between alkynones and cyclic enol silyl ethers was developed by using a chiral N,N'-dioxide-zinc(II) complex as a catalyst. This method functions well for a variety of terminal alkynes as well as cyclic enol silyl ethers, with good to excellent enantioselectivity (up to 97 % ee). This is also the first successful example for the catalytic enantioselective [2+2] cycloaddition of internal alkynes with cyclic enol silyl ethers to give fully substituted cyclobutenes. Meanwhile, the desired cyclobutene product can easily be transformed into fused cyclobutane derivatives.

Detection of Cytomegalovirus Antibodies Using a Biosensor Based on Imaging Ellipsometry.

BACKGROUND: Cytomegalovirus (CMV) is the most common infectious cause of mental disability in newborns in developed countries. There is an urgent need to establish an early detection and high-throughput screening method for CMV infection using portable detection devices. METHODS: An antibody analysis method is reported for the detection and identification of CMV antibodies in serum using a biosensor based on high spatial resolution imaging ellipsometry (BIE). CMV antigen (CMV-3A) was immobilized on silicon wafers and used to capture CMV antibodies in serum. An antibody against human immunoglobulin G (anti-IgG) was used to confirm the IgG antibody against CMV captured by the CMV-3A. RESULTS: Our results show that this assay is rapid and specific for the identification of IgG antibody against CMV. Further, patient serum was quantitatively assessed using the standard curve method, and the quantitative results were in agreement with the enzyme-linked immunosorbent assay. The CMV antibody detection sensitivity of BIE reached 0.01 IU/mL. CONCLUSIONS: This novel biosensor may be a valuable diagnostic tool for analysis of IgG antibody against CMV during CMV infection screening.

Scandium-catalyzed asymmetric 1,6-addition of 3-substituted oxindoles to linear dienyl ketones.

The first example of a N,N'-dioxide-Sc(III) -catalyzed 1,6-addition of 3-substituted oxindoles to dienyl ketones has been developed. This procedure tolerates a relatively wide range of 3-substituted oxindoles under mild conditions, facilitating the preparation of various chiral oxindoles with quaternary stereocenters. In addition, the reliable catalyst was found to be effective in the asymmetric 1,6-addition of both δ-unsubstituted and δ-methyl-substituted dienyl ketones, achieving excellent regioselectivities and enantioselectivities (up to>99 % ee).

Kinetic analysis of the weak affinity interaction between tris and lysozyme.

The biosensor based on total internal reflection imaging ellipsometry (TIRIE), regarded as an automotive real-time research approach for biomolecular interaction, is introduced to analyze the kinetic process of the weak interaction between tris and lysozyme. The experiment is performed by delivering lysozyme solution diluted to different concentrations to the biosensor substrate interface immobilized with tris. By applying pseudo-first-order interaction kinetics model, we are able to obtain the kinetic parameters from fitting experimental data. The calculated association rate constant and dissociation rate constant of tris and lysozyme interaction are in 10(-2) mol(-1) s(-1) and 10(3)s(-1) magnitude, respectively. To further improve TIRIE's ability for kinetically characterizing biomolecular interaction, a theoretical method to deduce associate rate constant before experiment is proposed.

Analysis of interactions between SNARE proteins using imaging ellipsometer coupled with microfluidic array.

The soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins are small and abundant membrane-bound proteins, whose specific interactions mediate membrane fusion during cell fusion or cellular trafficking. In this study, we report the use of a label-free method, called imaging ellipsometer to analyze the interactions among three SNAREs, namely Sec22p, Ykt6p and Sso2p. The SNAREs were immobilized on the silicon wafer and then analyzed in a pairwise mode with microfluidic array, leading us to discover the interactions between Ykt6p and Sso2p, Sec22p and Sso2p. Moreover, by using the real-time function of the imaging ellipsometer, we were able to obtain their association constants (K(A)) of about 10(4) M(-1). We argue that the use of imaging ellipsometer coupled with microfluidic device will deepen our understanding of the molecular mechanisms underlying membrane fusion process.

Highly diastereo- and enantioselective Michael addition of 3-substituted benzofuran-2(3H)-ones to 4-oxo-enoates catalyzed by lanthanide(III) complexes.

An efficient lanthanide(III)-catalyzed diastereo- and enantioselective Michael addition of 3-substituted benzofuran-2(3H)-ones to 4-oxo-enoates was developed. The desired adducts with contiguous quaternary-tertiary stereocenters were obtained in up to 99% yield with up to >95/5 dr and 98% ee.

Joint detection of tumor markers with imaging ellipsometry biosensor.

Tumor marker detection contributes to the early diagnosis of cancers. However, due to the lack of detection specificity, its results cannot act as a direct evidence to confirm cancer occurrence in clinic. Joint detection of tumor markers may improve the detection specificity. As a trial for clinical diagnosis of hepatocellular carcinoma, α-fetoprotein, α-l-fucosidase and ferritin have been combined and detected with a label-free, phase sensitive and high throughput imaging ellipsometry biosensor (IEB). Eighty-two sera have been quantitatively detected with IEB and the results are in agreement with the clinical standard approaches. Evaluated by receiver operating characteristic analysis, the specificity of joint detection improves remarkably with IEB for hepatocellular carcinoma. It can be foreseen that the joint detection of tumor markers with IEB has a potential for clinical cancer diagnosis.

Analysis of the interaction between tropomyosin allergens and antibodies using a biosensor based on imaging ellipsometry.

A biosensor based on high spatial resolution imaging ellipsometry has been studied to examine its role in the rapid detection and analysis of the tropomyosin allergen existing in crustaceans. This methodology has been established for detection of the tropomyosin allergen and includes ligand screening, the determination of sensitivity, and a comparison with traditional detection methods. Three kinds of monoclonal antibodies (2F9, 4C7, and 2H6) known to have a high bioactivity against the tropomyosin allergen were screened and separately immobilized as ligands on a silicon wafer surface, thus allowing them to capture the tropomyosin allergen. Resulting changes on the wafer surface were visualized in gray scale variation on an ellipsometry image. Images showed that these antibodies are able to recognize the presence of the tropomyosin allergen in shrimp and crab with sensitivity of 1 mg L(-1), and at a detecting time of approximately 30 min for an extracted sample. This preliminary study has shown that the detection of the tropomyosin allergen is rapid and specific when using this type of assay on products containing shrimp and crab. When compared with the enzyme-linked immunosorbent assay, the biosensor based on imaging ellipsometry is able to perform a fast label-free analysis.