Thiourea fused γ-amino alcohol organocatalysts for asymmetric Mannich reaction of ß-keto active methylene compounds with imines.

Catalytic functionality of new optically active thiourea fused γ-amino alcohols was examined in the asymmetric Mannich reaction of ß-keto active methylene compounds with imines to afford chiral Mannich products, ß-amino keto compounds, with continuous chiral centers, that are versatile synthetic intermediates for deriving various biologically active compounds. In particular, the thiourea fused γ-amino alcohols showed satisfactory catalytic activity in this reaction and afforded chiral Mannich products in excellent chemical yield (up to 88%) and stereoselectivities (up to syn : anti/93 : 7 dr, up to 99% ee).

New boro amino amide organocatalysts for asymmetric cross aldol reaction of ketones with carbonyl compounds.

Distinct types of new boron fused primary amino amide organocatalysts were designed and synthesized from commercially available amino acids. Their catalytic activities were investigated in asymmetric crossed aldol reaction of ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good chemical yields, moderate diastereoselectivity and good to excellent enantioselectivities (up to 94% yields, up to 90 : 10 dr, up to 94% ee).

Simple amino silyl ether organocatalyst for asymmetric hetero Diels-Alder reaction of isatins with enones.

New two catalysts component system comprising of a primary ß-amino silyl ethers as an organocatalyst and N-protected amino acids as a co-catalyst put together worked as an efficient organocatalyst system in the hetero Diels-Alder reaction of isatins with enones affording the chiral spirooxindole-tetrahydropyranones in good chemical yields and stereoselectivities (up to 94%, up to dr 78:22., up to 85% ee).

New small γ-turn type N-primary amino terminal tripeptide organocatalyst for solvent-free asymmetric aldol reaction of various ketones with aldehydes.

New small γ-turn type N-primary amino terminal tripeptides were synthesized and their functionality as an organocatalyst was examined in the asymmetric aldol reaction of various ketones with different aromatic aldehydes under solvent-free neat conditions to afford the desired chiral anti-aldol products in good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn : anti/13 : 87 dr, up to 99% ee).

Simple primary ß-amino alcohols as organocatalysts for the asymmetric Michael addition of ß-keto esters to nitroalkenes.

Simple primary ß-amino alcohols act as an efficient organocatalysts in the asymmetric Michael addition of ß-keto esters with nitroalkenes affording highly pure chiral Michael adducts. Also, both enantiomers of the adducts were obtained, depending on the specific catalyst used and reaction temperature.

Simple organocatalyst component system for asymmetric hetero Diels-Alder reaction of isatins with enones.

A simple two catalyst component system consisting of primary ß-amino alcohols as a catalyst and amino acids as a co-catalyst put together works as an efficient organocatalyst system in the hetero Diels-Alder reaction of isatins with enones to afford the chiral spirooxindole-tetrahydropyranones in good chemical yields and stereoselectivities (up to 86%, up to 85 : 15 dr., up to 95% ee).

Asymmetric synthesis of 1-substituted 2-azaspiro[3.3]heptanes: important motifs for modern drug discovery.

Highly diastereoselective addition of ethyl cyclobutanecarboxylate anions to Davis-Ellman's imines is reported. This methodology afforded the preparation of enantiomerically and diastereomerically pure 1-substituted 2-azaspiro[3.3]heptanes. This three-step procedure proceeded efficiently (yield up to 90%) and diastereoselectively (dr values up to 98 : 2). This methodology is applicable to the synthesis of 1-substituted 2-azaspiro[3.4]octane and 1-substituted 2-azaspiro[3.5]nonane.

Pd(II)/PhI(OAc)2 promoted direct cross coupling of glucals with aromatic acids.

A highly efficient oxidative C2-aroyloxylation of D-glucal with aromatic carboxylic acids has been achieved for the first time using 5 mol% Pd(OAc)2 and 1 equiv of PhI(OAc)2 to produce C2-aroyloxyglycals in good yields. The use of excess of PhI(OAc)2 (2 equiv) provides C2-acyloxyglycal exclusively.

Comparative evaluation of retention of prefabricated and conventional cast post: An in vitro study.

BACKGROUND AND OBJECTIVES: This study was conducted to evaluate the retention of various prefabricated posts and to compare them with that of the conventional cast post. MATERIALS AND METHODS: A sample of 60 freshly extracted single-rooted human mandibular first premolars were sectioned horizontally, 1 mm coronal to the cemento-enamel junction and randomly divided into four groups consisting of carbon fiber posts, glass fiber posts, stainless steel posts and cast metal posts. Cast metal post was the control group. Each group contained 15 specimen. The post space of 9 mm depth was prepared using specific drill supplied by the manufacturer. Resin patterns of the prepared post spaces were fabricated for 15 specimen and were cast in nickel chromium base metal alloy. All the posts were cemented with self-adhesive resin cement and mounted in acrylic cylinders. The teeth were subjected to tensile pull-out test using a universal testing machine. The force required to dislodge each post from the teeth was recorded. The data was analyzed using one-way analysis of variance and Bonferroni test. RESULTS: The bond strength of all the prefabricated posts was significantly lower than the conventional cast post. Among the prefabricated posts highest bond strength was obtained for prefabricated stainless steel post and lowest for carbon fiber posts. There was no significant difference in the mean bond strength obtained for stainless steel and glass fiber post. CONCLUSION: Though no single prefabricated post could achieve results close to the control group, most retentive among the experimental group were the stainless steel posts. However, conditions where nonmetallic posts are indicated most preferred type of post can be the glass fiber posts.

Effect of different cementation techniques on retained excess cement and uniaxial retention of the implant-supported prosthesis: an in vitro study.

PURPOSE: The aim of this study was to identify the different techniques of cementation (half filling, practice abutment, and venting) that will reduce the amount of retained cement and the effect of these techniques on retention of implant-supported prostheses. MATERIALS AND METHODS: Thirty implant-abutment assemblies were prepared and were subdivided further into three groups: half filling, practice abutment, and venting techniques. Crowns were prepared for each sample and cemented according to the respective techniques. The retention values were then determined using a universal testing machine, and the net weight of the retained cement was determined using a digital scale. RESULTS: Analysis of variance (ANOVA) tests revealed that there was not a significant difference in the retention values of the three cementation techniques, but a significant difference was observed in the amount of retained excess cement. Tukey honestly significant difference tests further showed that there was a significant difference in retained excess cement between the half-filling technique vs the venting and practice abutment techniques. CONCLUSION: The venting and practice abutment techniques are suitable methods for reducing retained excess cement with optimal retention values.

Effect of Ceramic Thickness and Luting Agent Shade on the Color Masking Ability of Laminate Veneers.

The main objective of the study was to recognize the effect of ceramic thickness and luting agent on the extent to which the restoration masks color variations that may be present in the underlying dental structure. Two pressable ceramics were used: Lithium disilicate reinforced (IPS e.max- Ivoclar Vivadent) and Leucite reinforced (Cergo- Dentsply). Fifteen ceramic discs were manufactured from each ceramic and divided into three groups, according to the thickness (0.5, 1, 1.5 mm). To simulate the color of a dark underlying dental structure, background discs, color C3, with 20 mm diameter, were made using resin composite. The ceramic discs with varying thicknesses were seated on the dark background of the resin composite with either resinous opaque cement or resinous cement. The color parameters were determined by the CIE Lab system of colors using a spectrophotometer and color differences (ΔE) were calculated. The results were then statistically analyzed, using ANOVA test and Tukey HSD test. The ΔE values of both ceramic systems were affected by both the luting agent and the ceramic thickness (P < 0.05). The use of an opaque luting agent resulted in an increase of the ΔE* values for all ceramics tested, regardless of the thickness. For the 1.5-mm thick veneers, higher values in the color parameters were obtained for both ceramic materials. The color masking ability of ceramics used for laminate veneers is significantly affected by the thickness of the ceramic and the shade of the luting agent used.

Structures of Na9[SO4]4X.2H2O2, where X = Cl or Br, in which the halide anions orchestrate extended orientation sequences of H2O2 solvate molecules.

Detailed structures of nonasodium tetrakis(sulfate) chloride diperhydrate, Na9[SO4]4Cl.2H2O2, and its novel bromide analogue are compared. Hydrogen peroxide could not be resolved in a previously reported Na9[SO4]4Cl.2H2O2 substructure. However, on lowering the symmetry to P4/n, and using reflection data based on full unit-cells, the H2O2 solvate can be clearly seen. Although H2O2 molecules are not directly bonded to the halide anions, they exert considerable influence on the eight sodium cations that constitute each halide's coordination shell so that H2O2 ordering can be linked to halide dimensions.