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From imine to amine: an unexpected left turn. Cis-? iron(ii) PNNP' precatalysts for the asymmetric transfer hydrogenation of acetophenone.

ABSTRACT: A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [-PR₂CH₂CH(OH)-]₂[Br]₂ R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH₂)₆]²⁺ to produce a new series of cis-? iron(ii) PNNP' precatalysts cis-?-[Fe(Br)(CO)(PNNP')]BPh₄ as a pair of diastereomers. The more stable orthophenylene amido group was chosen to imitate and replace the enamido moiety of a highly active iron precatalyst for the asymmetric transfer hydrogenation (ATH) of ketones in an attempt to prevent its deactivation caused by reduction of the enamido group. This objective was partially achieved using the complex with a PEt₂ group which catalyzed the transfer hydrogenation in isopropanol of 150?000 equivalents of acetophenone to racemic 1-phenylethanol. With a low acetophenone to catalyst ratio of 500 to 1, the catalytic activity was moderate and the enantiomeric excess (ee) of the product 1-phenylethanol ranged surprisingly from 94% (R) to 95% (S) depending on the nature of PR₂ and whether the precatalyst contained an imine or amine donor. The amine precatalyst with a PEt₂-group produced a more stable hydride species when activated, allowing the reaction mixture to be heated to 75 °C to obtain a TON of 8821 for acetophenone while retaining the high ee of 95% (S). The activation pathway in basic isopropanol (iPrOH) was studied for three precatalysts to elucidate that the cis-? precatalysts rearrange to form trans hydride complexes. The study suggests that the enantioselectivity of these complexes is determined by from which side of the PNNP' plane the hydride transfer occurs.

SUBMITTER: Demmans KZ

PROVIDER: S-EPMC5627452 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP' precatalysts for the asymmetric transfer hydrogenation of acetophenone.

Demmans Karl Z KZ Seo Chris S G CSG Lough Alan J AJ Morris Robert H RH

Chemical science 20170714 9

A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [-PR2CH2CH(OH)-]2[Br]2 R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH2)6]2+ to produce a new series of cis-β iron(ii) PNNP' precatalysts cis-β-[Fe(Br)(CO)(PNNP')]BPh4 as a pair of diastereomers. The more stable orthop ...[more]

PMID: 28989679

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Project description:Anatomically and functionally defined neuron types are sometimes further classified into individual subtypes based on unique functional or molecular properties. To better understand how developmental programs controlling neuron type specification are mechanistically linked to programs controlling neuronal subtype specification, we have analyzed a neuronal subtype specification program that occurs across the left/right axis in the nervous system of the nematode C. elegans. A terminal selector transcription factor, CHE-1, is required for the specification of the ASE neuron class, and a gene regulatory feedback loop of transcription factors and miRNAs is required to diversify the two ASE neurons into an asymmetric left and right subtype (ASEL and ASER). However, the link between the CHE-1-dependent ASE neuron class specification and the ensuing left-right subtype specification program is poorly understood. We show here that CHE-1 has genetically separable functions in controlling bilaterally symmetric ASE neuron class specification and the ensuing left-right subtype specification program. Both neuron class specification and asymmetric subclass specification depend on CHE-1-binding sites (;ASE motifs') in symmetrically and asymmetrically expressed target genes, but in the case of asymmetrically expressed target genes, the activity of the ASE motif is modulated through a diverse set of additional cis-regulatory elements. Depending on the target gene, these cis-regulatory elements either promote or inhibit the activity of CHE-1. The activity of these L/R asymmetric cis-regulatory elements is indirectly controlled by che-1 itself, revealing a feed-forward loop configuration in which che-1 restricts its own activity. Relative binding affinity of CHE-1 to ASE motifs also depends on whether a gene is expressed bilaterally or in a left/right asymmetric manner. Our analysis provides insights into the molecular mechanisms of neuronal subtype specification, demonstrating that the activity of a neuron type-specific selector gene is modulated by a variety of distinct means to diversify individual neuron classes into specific subclasses. It also suggests that feed-forward loop motifs may be a prominent feature of neuronal diversification events.

Dataset Information

From imine to amine: an unexpected left turn. Cis-? iron(ii) PNNP' precatalysts for the asymmetric transfer hydrogenation of acetophenone.

Publications

From imine to amine: an unexpected left turn. <i>Cis</i>-β iron(ii) PNNP' precatalysts for the asymmetric transfer hydrogenation of acetophenone.

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