Asymmetric Building Blocks Research Articles

Controlling the Chirality of DNA Nanocages

Playing DNA Twister: By using asymmetric DNA building blocks, self-assembled DNA nanocages that are chiral on the nanoscale have been designed. The resulting DNA nanocages have been characterized with a variety of methods. Such chiral control could be useful for tuning the photonic/optical properties of DNA-templated nanostructures.

A novel Co3+-based asymmetrical building block: Heterobimetallic metallacycles versus coordination networks

Abstract A new Co3 +-based asymmetrical building block (1) offering both 2-pyridyl and 3-pyridyl appended groups has been synthesized and utilized for preparing heterobimetallic systems. The reactions of 1 with secondary metals afforded {Co3 +–Zn2 +} metallacycle (2), {Co3 +–Cd2 +} metallacycle‐based coordination polymer (3) and a {Co3 +–Hg2 +} coordination chain (4). The crystallographic studies reveal the importance of asymmetrical building block in generating unique structural motifs.

Umpolung Catalysis in Benzoin-type and Stetter-type Reactions: From Enzymatic Performances to Bio-mimetic Organocatalytic Concepts

The umpolung bezoin-type and Stetter-type reactions are valuable synthetic strategies to furnish an ample number of important compounds and asymmetric building blocks. Biocatalysis is contributing to this field with several thiamine-dependent lyases, enzymes that are able to catalyze these reactions under mild reaction conditions with high yields and enantioselectivities. Furthermore, recent developments in that field have led to an enzymatic process for the asymmetric Stetter reaction. Likewise, taking Nature as inspiration, several bio-mimetic, organocatalytic approaches have been developed for these syntheses as well. Herein one important strategy comprises the development of “holoenzyme” microenvironments for the organocatalyst, what create hydrophobic conditions that may mimic the role of an enzyme (apoenzyme). That has been achieved by several ways, like set-up of micellar systems, anchoring catalysts to long hydrophobic, aliphatic structures, or by immobilizing organocatalysts to several supports like cyclodextrins, polystyrenes, etc. Another important strategy to mimic enzymatic performances is represented by catalyst design. Herein, starting from seminal work dealing with thiazolium salts - bio-mimetic approach of thiamine, cofactor for enzymes -, impressive developments have been achieved with the establishment of triazolium catalysts as powerful organocatalysts for many asymmetric reactions. The present article will provide an overview from biocatalytic concepts to bio-mimetic possibilities in the field of benzoin-type and Stetter-type reactions. Keywords: Biocatalysis, organocatalysis, biomimetic, benzoin, acyloin, stetter, Kurasoin, Bupropion, Ephedrine, Ketoacid decarboxylase (KdCA), Holoenzyme, apoenzyme, micellar, Phenylaceytlcarbinol, Enantiomeric excess

Hydrothermal Syntheses and Structural Characterizations of Polyoxometalate (Mo/W) Compounds Consisting of M-L Cations, (M = Mn, Co, Ni, Cu, Zn; L = 3-(2-Pyridyl)pyrazole)

A series of molybdenum/tungsten polyoxometalate compounds, namely, [(MII(HL)2)Mo3O10] (M = Mn (1), Co (2), Ni (3)), [CuII2(L)2(HL)2]2(Mo8O26) (4), [Zn(HL)2(MoO4)]2·HL·4H2O (5), [CuII4(L)6WO4)]·3H2O (6) (HL = 3-(2-pyridyl)pyrazole), were designed and synthesized under hydrothermal conditions. X-ray diffraction analyses reveal that compounds 1−3 have an isostructural wavelike chain structure consisting of the asymmetric building blocks of [Mo3O10], in which the ratio of octahedron {MoO6} and square pyramid {MoO5} is 1:2. The hexacoordinated transitional metal cation, just like one “anchor” to fix the above wavelike chain, is linked by two terminal oxygen atoms belonging to two edged asymmetric molybdate [Mo3O10]2− units, and further chelated by two 3-(2-pyridyl)pyrazole ligands. Although a similar synthetic method in preparation of 1−5 was employed, compounds 4 and 5 show a completely different structure compared to compounds 1−3. Compound 4 is composed of two separate parts of the [CuII2(L)2(HL)2]2+ dimer and the ε-[Mo8O26]4− unit. Compound 5 consists of a bimetallic tetranuclear cluster that is constructed from corner-sharing {MoO4} tetrahedra and {ZnN4O2} distorted octahedron forming a cyclic {Zn2Mo2O4} core. For compound 6, a one-dimensional structure is composed of WO42− linked by the centrosymmetric tetranuclear copper grids, in which two approximately planar [CuII(L)]2 units with an inversion center stack parallel and face-to-face linked by two additional deprotonated ligands of L−1 perpendicularly.

Functionalised butanediacetal-protected 1,2-diols as suitable partners for Pd-catalysed cross-coupling reactions

A new method for the synthesis of dienes and enynes containing chiral 1,2-diols is described. The strategy is based on the Pd-catalysed cross-coupling reactions of a series of vinyl and alkynyl asymmetric butanediacetal-protected building blocks. After the coupling, removal of the protecting group leads to the desired functionalised dienes and enynes.

The Choice of Phosphane Reagent in Fukuyama−Mitsunobu Alkylation: Intramolecular Selectivity Between Primary and Secondary Alcohols in the Preparation of Asymmetric Tetraamine Building Blocks for Synthesis of Philanthotoxins

AbstractPhilanthotoxin‐433 (PhTX‐433) is a polyamine wasp toxin that antagonizes certain ionotropic receptors noncompetitively. Four analogues of PhTX‐433, C‐methylated in the polyamine chain, were synthesized from (RS)‐1,3‐butanediol, two diamine building blocks, and an activated/protected tyrosine derivative. Use of a phosphane reagent more bulky than trimethylphosphane gave a high intramolecular selectivity between primary and secondary hydroxy groups in the Fukuyama−Mitsunobu reaction. Thus, trimethylphosphane proved to be the only phosphane reagent that enabled alkylation of 2‐nitrobenzenesulfonamides with a wide range of secondary alcohols, whereas tributylphosphane was selective for primary alcohol groups. This selectivity was utilized to obtain orthogonally protected, asymmetric, branched tetraamines, employed for solution‐phase synthesis of philanthotoxin analogues. The branched philanthotoxin analogues thus obtained were tested in an electrophysiological assay using rat brain ionotropic glutamate receptors expressed in Xenopus laevis oocytes. Their potencies proved to be similar to the corresponding nonbranched analogues. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

ChemInform Abstract: Electrophilic Amination of Ketone Enolates Mediated by the DiTOX Asymmetric Building Block: Enantioselective Formal Synthesis of α‐Aminoacids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electrophilic Amination of Ketone Enolates Mediated by the DiTOX Asymmetric Building Block: Enantioselective Formal Synthesis of α-Aminoacids

Diastereoselective electrophilic amination of enolates derived from 2-acyl-1,3-dithiane 1-oxides is used as the key step for an enantioselective synthesis of two α-hydrazido carboxylic acids, well-known precursors of α-amino acids.

Perceptual differences in fetal alcohol effect boys performing a modeling task.

Perceptual differences were examined for four boys identified with fetal alcohol effect (FAE) and labeled learning disabled for educational purposes. Without a model, all FAE boys built asymmetrical building block designs with no stacking of blocks. When the boys were shown a short videotape of a peer building a simple symmetrical structure with one-layer stacking of blocks, none of the FAE boys successfully imitated. They continued to place blocks randomly on the floor surface with no stacking or layering. This limited study suggests modeling perceptual tasks may not be an effective teaching strategy for children identified with fetal alcohol effect and such children may not be able to learn new skills using demonstration or modeling.

ChemInform Abstract: The Development and Application of 1,3‐Dithiane 1‐Oxide Derivatives as Chiral Auxiliaries and Asymmetric Building Blocks for Organic Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective synthesis of α-hydroxyketones using the ditox asymmetric building block

The 2-( R)and 2-( S)-hydroxy-1-phenylbutan-1-ones have been prepared in high enantiomeric excesses and in five steps from propanal using a dithiane oxide unit as an asymmetric building block and a modified Sharpless enantioselective sulphur oxidation as the source of Chirality.

Asymmetric synthesis of allylic sulfones useful as asymmetric building blocks.

Asymmetric synthesis of allylic sulfones useful as asymmetric building blocks.

The enantioselective synthesis of simplified southern-half fragments of soraphen A

The compound 2 comprises a southern-half subunit of the fungicidal macrolide soraphen A 1. It was prepared by a Meinwald reaction of the enolate of S-7 with the lactone S-8 . Its enantiomer and diastereomers were synthesized in a similar manner. The lactone S-8 and its enantiomer R-8 were prepared by three different routes, including the enantioselective catalytic reduction of the β-keto ester 17. These lactones are new and potentially useful as C-5 asymmetric building blocks.

ChemInform Abstract: Enantioselective Synthesis of (R)‐(‐)‐2,6‐Dimethyl Heptanoic Acid: The First Application of the DITOX Asymmetric Building Block

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective synthesis of (R)-(−)-2,6-dimethyl heptanoic acid: The first application of the DITOX asymmetric building block

The 1,3-dithiane 1-oxide (DITOX) asymmetric building block/chiral auxiliary has been used to prepare ( R)-(−)-2,6-dimethyl heptanoic acid (1), a simple derivative of citronellal, in two steps from (2).

ChemInform Abstract: Diastereoselectivity in the Addition of Grignard Reagents to Ketones Controlled by the 1,3‐Dithiane 1‐Oxide Asymmetric Building Block.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diastereoselectivity in the addition of grignard reagents to ketones controlled by the 1,3-dithiane 1-oxide asymmetric building block

2-Acyl-1,3-dithiane 1-oxides undergo diastereoselective addition of Grignard reagents; the degree of selectivity observed is highly dependent upon the solvent and the halide counter-ion used; very high selectivities have been observed under certain reaction conditions.

Symmetry in building block design for learning disabled and nonlearning disabled boys.

This study examined perceptual differences in symmetry with and without a model between 21 learning disabled boys with reading deficits and 28 learning disabled boys with deficits in mathematics. 55 nonlearning disabled boys served as controls. All boys were in Grades 3, 4, or 5. Without a model, all learning disabled boys built significantly more asymmetrical building block designs than nonlearning disabled boys. However, with a model, all learning disabled boys could imitate the model, but it took them longer to complete the task successfully. All boys appeared to have difficulty in modeling asymmetrical tasks, taking more time for task completion after seeing an asymmetrical model. This study suggests modeling perceptual tasks might be an effective teaching strategy for such children.