Reference

a-Amino acids and N-protected a-amino aldehydes by stereoselective additions of a chiral vinyllithium reagent to sulfonyl imines

a-Amino acids and N-protected a-amino aldehydes by stereoselective additions of a chiral vinyllithium reagent to sulfonyl imines. Braun, Manfred; Opdenbusch, Kersten (Inst.Several substances are used for example 402-46-0 which is its cas registry number. Organische Chem. Makromolekulare Chem., Univ. Duesseldorf, Duesseldorf D-40225, Germany). Liebigs Annalen/Recueil, (1), 141-154 (English) 1997 VCH. CODEN: LIARFV. DOCUMENT TYPE: Journal CA Section: 34 (Amino Acids, Peptides, and Proteins) The vinyllithium reagent (S,E)-MeO(CH2)2OCH2OCHMeCH:CBrLi, readily generated from the appropriate dibromoalkene by Br/Li exchange, adds stereoselectively to mesitylsulfonyl imines to give the bromoalkenes I [R = Ph, 4-MeOC6H4, 4-(Me2CHCMe2Me2SiO)C6H4, Me2CHCH2, Me2CH, Me3C] in 398% d.e. after column chromatog. Bromoalkenes I [R = Ph, 4-MeOC6H4, 4-(Me2CHCMe2Me2SiO)C6H4, Me2CHCH2] are submitted to ozonolysis in MeOH to give the corresponding a-mesitylsulfonylamino esters (S)-2,4,6-Me3C6H2NHCRCO2Me which were hydrolyzed to deliver N-protected a-amino acids in >95% ee. a-Mesitylsulfonylamino aldehydes (S)-2,4,6-Me3C6H2NHCRCHO are available when I (R = Ph, Me2CHCH2, Me2CH, Me3C) is first debrominated and subsequently ozonized. To avoid racemization, the aldehydes are not purified but submitted to a Mukaiyama-type aldol addn. whereby hydroxy esters (S,S)-2,4,6-Me3C6H2NHCRCHOHCMe2CO2Me are formed as single diastereomers in a chelate-controlled reaction. The relative configuration of the latter is proven by conversion into the oxazolidinones II whose optical purity is detd. to exceed 92% ee by 1H NMR in the presence of chiral shift reagents. The sulfonyl imines 4-RC6H4SO2N:CHPh (R = H, Me2N, MeO, Me, F, Cl, CF3, NO2) are also allowed to react with (S,E)-MeO(CH2)2OCH2OCHMeCH:CBrLi to give mixts. of the corresponding diastereomers III. The logarithms of the diastereomeric ratios of the latter correlate with Hammett's s-values. .

The use of p-fluorobenzenesulfonyl chloride as a reagent for studies of proteins by fluorine nuclear magnetic resonance

The use of p-fluorobenzenesulfonyl chloride as a reagent for studies of proteins by fluorine nuclear magnetic resonance. Liao, Ta Hsiu; Berlin, K. Darrell (Dep. Biochem., Oklahoma State Univ., Stillwater, OK 74078, USA). Anal. Biochem., 148(2), 365-75 (English) 1985. CODEN: ANBCA2. ISSN: 0003-2697. DOCUMENT TYPE: Journal CA Section: 9 (Biochemical Methods) Section cross-reference(s): 6, 77 The reagent p-fluorobenzenesulfonyl chloride modifies the protein side chains of tyrosine, lysine, and histidine and the a-NH2 group. The p-fluorobenzenesulfonyl (Fbs-) group, identified by the 19F NMR signal, exhibits a different 19F chem. shift for each functional group modified. The Fourier-transformed spectra of the Fbs- group displayed the expected 9-line multiplet in Fbs-amino acids and simple Fbs-peptides but not i n the Fbs-proteins, where the resoln. was reduced. Lysozyme, RNase, DNase, and chymotrypsin react with this reagent and each Fbs-protein exhibits a distinctive pattern of 19F NMR signals due to the label, suggesting that the reaction of the reagent varies with the reactivity of the side chains in a protein. The 3 major 19F signals of the unfolded Fbs-RNase in 8M urea are due to the Fbs label on the imidazolium, a-NH2, and e-NH2 groups. Based upon results from amino acid and 19F NMR analyses of the tryptic-chymotryptic peptides of Fbs-RNase, portions of the imidazolium and e-NH2 resonances were assigned to the Fbs-label on His-105 and Lys-41, resp., whereas the a-NH2 resonance was entirely due to the Fbs-label on the a-NH2 of Lys-1. Because Fbs-RNase has an unchanged, near-UV CD spectrum and because it retains ~80% of the RNase activity, the conformation of Fbs-RNase is probably not altered from the folded conformation of the native enzyme. Upon unfolding in 8M urea or heating at 70°, Fbs-RNase gave a 19F NMR spectrum differing from that of the folded Fbs-RNase. In the presence of uridylic acid, Lys-41 was the only residue protected from modification by the reagent, with a concomitant redn. of the e-NH2 resonance, the RNase thus modified was fully active.In this experiment, several chemicals are used like 402-46-0 Hence, 19F NMR anal. of proteins after reaction with p-fluorobenzenesulfonyl chloride, provided not only information about the protein conformation but also direct measurements of the modification status. .