58420-91-0Relevant academic research and scientific papers
Carbon-13 Nuclear Magnetic Resonance in Isotopically Enriched High-spin Iron(III) Porphyrins: ?-Electron Spin Distribution
Mispelter, Joel,Momenteau, Michel,Lhoste, Jean-Marc
, p. 1729 - 1734 (1981)
The 13C n.m.r. spectrum of high-spin chloro(5,10,15,20-tetraphenylporphyrinato)iron(III) has been unambiguously assigned using pophyrins isotopically enriched at selected positions.The unexpected linewidth of the resonances of the porphyrin core carbons is explained by the dipolar interaction of the carbon nuclei with the ligand unpaired ?-electron spin densities.This interaction is the dominant mechanism of relaxation for the meso carbons and the pyrrole β carbons.The relative contribution of this mechanism increases for nuclei farther from the iron ion.As a result, it is also the dominant mechanism for the relaxation of the porphyrin protons.The ? spin distribution on the porphyrin ring has been derived from the dipolar contribution to the linewidth for the carbon nuclei.Furthermore, the experimental β proton resonance linewidth can be interpreted only by considering a normalized iron spin density lower than unity.A value of 3.5/5 is proposed in good agreement with earlier molecular-orbital calculations.This analysis provides a set of self-consistent data for the quantitative description of the various contributions to the observed shifts, including the ligand-centred pseudo-contact contribution, and to the linewidth for both the proton and the carbon nuclei.
Synthesis of 4-thia-[6-13C]lysine from [2-13C] glycine: Access to site-directed isotopomers of 2-aminoethanol, 2-bromoethylamine and 4-thialysine
Maity, Amarendra Nath,Shaikh, Ajam C.,Srimurugan, Sankareswaran,Wu, Chi-Ju,Chen, Chinpiao,Ke, Shyue-Chu
, p. 309 - 315 (2012)
4-Thialysine (S-(2-aminoethyl)-L-cysteine) is an analog of lysine. It has been used as an alternative substrate for lysine in enzymatic reactions. Site-directed isotopomers are often needed for elucidation of mechanism of reactions. 4-Thialysine can be synthesized by reacting cysteine with 2-bromoethylamine, an important reagent in chemicalmodification rescue (CMR) of proteins. Here, we present the synthesis of 4-thia-[6-13C]lysine, one of the isotopomers of 4-thialysine, from commercially available starting material [2-13C]glycine via formation of five intermediates including 2-amino[2-13C]ethanol and 2-bromo[1-13C]ethylamine. The compounds were characterized using various spectroscopic techniques. Moreover, we discuss that our strategy would provide access to site-directed isotopomers of 2-aminoethanol, 2-bromoethylamine and 4-thialysine. Biological activity of 4-thia-[6-13C]lysine was tested in the enzymatic reaction of lysine 5,6-aminomutase. Springer-Verlag 2010.
Highly enantioselective ruthenium/PNNP-catalyzed imine aziridination: Evidence of carbene transfer from a diazoester complex
Egloff, Joel,Ranocchiari, Marco,Schira, Amata,Schotes, Christoph,Mezzetti, Antonio
supporting information, p. 4690 - 4701 (2013/09/23)
The ruthenium/PNNP complexes [RuCl(Et2O)(PNNP)]Y (Y = PF 6, 4PF6; BF4, 4BF4; or SbF 6, 4SbF6) (10 mol %) catalyze the enantioselective aziridination of imines with ethyl diazoacetate (EDA) as carbene source (PNNP = (1S,2S)-N,N′-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine) . The highest enantioselectivity was obtained with 4SbF6, which aziridinated N-benzylidene-1,1-diphenylmethanamine (5a) to cis-ethyl 1-benzhydryl-3-phenylaziridine-2-carboxylate (cis-6a) with 93% ee at 0 C. To the best of our knowledge, this is the highest enantioselectivity ever obtained in transition metal-catalyzed asymmetric aziridination. Aziridine yields were overall moderate to low (up to 33% isolated yield of the cis isomer) because of the competitive formation of diethyl maleate (7). The scope of the catalyst was studied with p- and m-substituted imines. NMR spectroscopic studies with 13C- and 15N-labeled EDA indicate that aziridine 6a is formed by carbene transfer from an EDA complex, [RuCl(EDA)(PNNP)]PF6 (8), to the imine. The observation of a dinitrogen complex (9) gives further support to this mechanism. The EDA adduct 8 decomposes to the carbene complex [RuCl(CHCO2Et)(PNNP)]+ (10), whose reaction with EDA gives diethyl maleate. This unprecedented mechanism is rationalized on the basis of the nucleophilic nature of diazoalkanes, which is enhanced by coordination to a π-back-donating metal such as ruthenium(II).
