Search results for "SELECTIVITY"

A Molecular Electron Density Theory Study of the [3+2] Cycloaddition Reaction of Pseudo(mono)radical Azomethine Ylides with Phenyl Vinyl Sulphone

2022

The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY), derived from isatin and L-proline, with phenyl vinyl sulphone has been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. ELF topological analysis of AY classifies it as a pseudo(mono)radical species with two monosynaptic basins at the C1 carbon, integrating a total of 0.76 e. While vinyl sulphone has a strong electrophilic character, AY is a supernucleophile, suggesting a high polar character and low activation energy for the reaction. The nucleophilic Parr functions indicate that the pseudoradical C1 carbon is the most nucleophilic center. The 32CA reaction presents an activat…

Asymmetric Synthesis of Spirocyclic β-Lactams through Copper-Catalyzed Kinugasa/Michael Domino Reactions

2018

The first copper-catalyzed highly chemo-, regio-, diastereo-, and enantioselective Kinugasa/Michael domino reaction for the desymmetrization of prochiral cyclohexadienones is described. In the presence of a chiral copper catalyst, alkyne-tethered cyclohexadienones couple with nitrones to generate the chiral spirocyclic lactams with excellent stereoselectivity (up to 97 % ee, >20:1 dr). The new method provides direct access to versatile highly functionalized spirocyclic β-lactams possessing four contiguous stereocenters, including one quaternary and one tetra-substituted stereocenter.

Stereoselective Synthesis of Microcarpalide

2002

The first total synthesis of the naturally occurring nonenolide, microcarpalide, is described. The key step in the synthesis was the ring-closing metathesis of a dienic ester prepared in turn by coupling an acid and an alcohol stereoselectively synthesized from (S,S)-tartaric acid and (R)-glycidol, respectively. [structure: see text]

Stereoselective Synthesis of the Cytotoxic Macrolide FD-891

2006

[reaction: see text] A total synthesis of the naturally occurring, cytotoxic macrolide FD-891 is described. Three fragments were first stereoselectively constructed using mainly asymmetric aldol and allylation reactions. The complete framework was then assembled using two Julia-Kocienski olefinations to connect the three fragments and a Yamaguchi reaction to close the macrolactone ring.

Stereoselective solid-phase synthesis of chiral piperidine derivatives by using an immobilized galactose auxiliary.

2003

Pillar[n]arenes-a Novel, Highly Promising Class of Macrocyclic Host Molecules

2014

Since 2008 a new field of supramolecular chemistry has developed rapidly: the chemistry of pillar[n]arenes. These “younger brothers and sisters” of calixarenes are conveniently accessible and extremely guest-friendly. Guests from many different classes of organic compounds are welcome. Nevertheless, a high selectivity for the threading of guest molecules in the macrocyclic cavities can be achieved. The complex stability is characterized by association constants Ka between 10 and 1×108 M−1. The rate constants of the threading vary over several orders of magnitude. The focus of this article lies on the preparation (sections 2 and 3) and the structures (section 4) of pillar[n]arenes (n=5–10) i…

Molecular simulation of mixed gas hydrates in astrophysical conditions

2020

In this PhD work, numerical simulation methods have been used in order to model clathrate hydrates at the molecular scale, in thermodynamic conditions typical of astrophysical contexts. The aim was to characterize the trapping abilities of those peculiar structures of water, by means of the tools used in adsorption studies. The results presented in the present thesis are focused on a couple of chemical species which are found to be abundant in our astrophysical vicinity and are quite similar: carbon monoxide, CO, and nitrogen, N2. Thus, the single-component clathrates of CO and N2, and the mixed hydrate CO-N2 have been studied, mainly using grand canonical Monte Carlo simulations. First, th…

Novel Hydrazine Molecules as Tools To Understand the Flexibility of Vascular Adhesion Protein-1 Ligand-Binding Site: Toward More Selective Inhibitors

2011

Vascular adhesion protein-1 (VAP-1) belongs to a family of amine oxidases. It plays a role in leukocyte trafficking and in amine compound metabolism. VAP-1 is linked to various diseases, such as Alzheimer's disease, psoriasis, depression, diabetes, and obesity. Accordingly, selective inhibitors of VAP-1 could potentially be used to treat those diseases. In this study, eight novel VAP-1 hydrazine derivatives were synthesized and their VAP-1 and monoamine oxidase (MAO) inhibition ability was determined in vitro. MD simulations of VAP-1 with these new molecules reveal that the VAP-1 ligand-binding pocket is flexible and capable of fitting substantially larger ligands than was previously believ…

Stereoselective Synthesis and Cytoselective Toxicity of Monoterpene-Fused 2-Imino-1,3-thiazines

2014

Starting from pinane-, apopinane- and carane-based 1,3-amino alcohols obtained from monoterpene-based β-amino acids, a library of monoterpene-fused 2-imino-1,3-thiazines as main products and 2-thioxo-1,3-oxazines as side-products were prepared via two- or three-step syntheses. When thiourea adducts prepared from 1,3-amino alcohols and aryl isothiocyanates were reacted with CDI under mild conditions, O-imidazolylcarbonyl intermediates were isolated which could be transformed to the desired 1,3-thiazines under microwave conditions. 1,3-Thiazines and 2-thioxo-1,3-oxazine side-products could also be prepared in one-step reactions through the application of CDI and microwave irradiation. The rin…

Structure Determination of Photoproducts of Anthracenes with (Arylmethoxymethyl) Sidechains

2007

Irradiation of 9-(arylmethoxymethyl)anthracenes 3 leads either to a cyclomer and cyclodimer mixture (3a  4a,5a), to selectively formed dimers (3b  5b), or a selectively formed cyclomer (3c  4c). The [4π+4π]cyclodimerization is under the conditions used a regioselective head-to-tail process. In the crystals of the dimers 5a,b, the sidechains are attached in an antiperiplanar position related to the CC bonds generated in the dimerization. In solutions, however, the structures consist of three rotamers the equilibration of which was studied by temperature-dependent NMR spectra. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)