| 1. |
- Butts, Craig P, et al.
(författare)
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Structure-based rationale for selectivity in the asymmetric allylic alkylation of cycloalkenyl esters employing the Trost 'Standard Ligand' (TSL): isolation, analysis and alkylation of the monomeric form of the cationic eta(3)-cyclohexenyl complex [(eta(3)-c-C6H9)Pd(TSL)]+.
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:29, s. 9945-57
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Tidskriftsartikel (refereegranskat)abstract
- The solution-phase structures of the monomeric forms of the cationic Pd-eta(3)-allyl and Pd-eta(3)-cyclohexenyl complexes [Pd(R,R)-1(eta(3)-C(3)H(5))](+) (7(+)) and [Pd(R,R)-1(eta(3)-C(6)H(9))](+) (8(+)) bearing the trans-cyclohexylenediamine-based Trost 'Standard Ligand' (R,R)-1 have been elucidated by NMR, isotopic labeling and computation. In both complexes, (R,R)-1 is found to adopt a C(1)-symmetric conformation, leading to a concave shape in the 13-membered chelate in which one amide group in the chiral scaffold projects its NH unit out of the concave surface in close vicinity to one allyl terminus. The adjacent amide has a reversed orientation and projects its carbonyl group out of the concave face in the vicinity of the opposite allyl terminus. Stoichiometric and catalytic asymmetric alkylations of [8(+)][X(-)] by MCHE(2) (E = ester, M = 'escort' counterion, X = Pd allyl counterion) show the same selectivities and trends as have been reported for in situ-generated catalysts, and a new model for the enantioselectivity has been explored computationally. Three factors are found to govern the regioselectivity (pro-S vs pro-R) of attack of nucleophiles on the eta(3)-C(6)H(9) ring in 8(+) and thus the ee of the alkylation product: (i) a pro-R torquoselective bias is induced by steric interaction of the eta(3)-C(6)H(9) moiety with one phenyl ring of the ligand; (ii) pro-S delivery of the nucleophile can be facilitated by hydrogen-bonding with the concave orientated amide N-H; and (iii) pro-R delivery of the nucleophile can be facilitated by escort ion (M) binding to the concave orientated amide carbonyl. The latter two opposing interactions lead to the selectivity of the alkylation being sensitive to the identities of X(-) and M(+). The generation of 8(+) from cyclohexenyl ester substrate has also been explored computationally. The concave orientated amide N-H is able to activate the leaving group of the allylic ester by hydrogen bonding to its carbonyl group. However, this interaction is only feasible for the (S)-enantiomer of substrate, leading to the prediction of a powerful kinetic resolution (k(S) >> k(R)), as is found experimentally. This new model involving two regiochemically distinct (NH) and (CO) locations for nucleofuge or nucleophile binding, may prove of broad utility for the interpretation of the selectivity in asymmetric allylic alkylation reactions catalyzed by Pd complexes of (R,R)-1 and related ligands.
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| 2. |
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| 3. |
- Pupier, Marion, et al.
(författare)
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NMReDATA, a standard to report the NMR assignment and parameters of organic compounds
- 2018
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Ingår i: Magnetic Resonance in Chemistry. - : John Wiley & Sons. - 0749-1581 .- 1097-458X. ; 56:8, s. 703-715
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Tidskriftsartikel (refereegranskat)abstract
- Even though NMR has found countless applications in the field of small molecule characterization, there is no standard file format available for the NMR data relevant to structure characterization of small molecules. A new format is therefore introduced to associate the NMR parameters extracted from 1D and 2D spectra of organic compounds to the proposed chemical structure. These NMR parameters, which we shall call NMReDATA (for nuclear magnetic resonance extracted data), include chemical shift values, signal integrals, intensities, multiplicities, scalar coupling constants, lists of 2D correlations, relaxation times, and diffusion rates. The file format is an extension of the existing Structure Data Format, which is compatible with the commonly used MOL format. The association of an NMReDATA file with the raw and spectral data from which it originates constitutes an NMR record. This format is easily readable by humans and computers and provides a simple and efficient way for disseminating results of structural chemistry investigations, allowing automatic verification of published results, and for assisting the constitution of highly needed open-source structural databases.
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| 4. |
- Wieske, Hermina, 1994-
(författare)
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Bringing Structure to Drug Discovery
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Drug discovery is aided by structural information. The type of structural information needed depends on the question at hand. The methods that can be used to determine the absolute configuration of a newly synthesised compound are different from those needed to study ligand binding. This thesis employs a set of structural techniques to study a variety of research questions.NMR methods were used to understand the binding of an inhibitor to an enzyme responsible for antibiotic resistance. This thesis describes the backbone resonance assignment of the enzyme and the investigation of the protein-ligand interaction. The binding-site as well as the binding-affinity were investigated.Obtaining insights into the passive membrane permeability of unconventionally large drugs was achieved by looking at their solution ensembles in polar and apolar environments. NMR experiments were used to obtain the solution ensembles of eight antimicrobial and antiviral drugs.One of the antiviral drugs was studied by MicroED, a new methodology capable of obtaining crystal structures. MicroED requires less material, smaller crystals and the crystals can be of lower quality as compared to conventional X-ray diffraction. This thesis shows that MicroED can be used to obtain the crystal structure of a flexible small molecule that is challenging to elucidate by X-ray crystallography.The final study of this thesis investigated the applicability of time-saving sampling schemes for the acquisition of quantitative NOESY data. It explores different variables, but none of the investigated conditions lead to the level of accuracy needed for NOE-based distance determination.
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