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Blocking Group (blocking + group)
Selected AbstractsStereo- and Regioselectivity in an Intramolecular Nitrone,Alkene Cycloaddition of Hept-6-enoses with a trans -Acetonide Blocking GroupCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2009Abstract From sugar to cycloadduct: The effect of the trans -acetonide blocking group and the stereochemistry of the substituents on the regio- and stereoselectivity in the intramolecular nitrone,alkene cycloaddition (INAC) reaction of hept-6-enoses (see scheme) is reported and studied by using theoretical analysis. The positional effect of the trans -acetonide blocking group and the effect of the stereochemistry of the substituents on the regio- and stereoselectivity in intramolecular nitrone,alkene cycloaddition (INAC) reactions of hept-6-enoses are reported. Hept-6-enoses with a 2,3- trans -acetonide group were reacted with N -alkyl hydroxylamine to give a mixture of exo and endo cycloadducts (cyclohexanols and cycloheptanols, respectively). Complete formation of endo cycloadducts (cycloheptanols) was realized for the INAC reaction of hept-6-enoses containing a 3,4- trans - O -isopropylidene ring. Similarly, reaction of a hept-6-enose possessing a 4,5- trans -acetonide group surprisingly afforded exo cycloadducts (cyclohexanols) exclusively. The regio- and stereochemical outcomes of these reactions were rationalized on the basis of transition-state energies obtained by computation. [source] Tandem electrospray mass spectrometric studies of proton and sodium ion adducts of neutral peptides with modified N- and C-termini: synthetic model peptides and microheterogeneous peptaibol antibioticsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2006Varatharajan Sabareesh The fragmentations of [M+H]+ and [M+Na]+ adducts of neutral peptides with blocked N- and C-termini have been investigated using electrospray ion trap mass spectrometry. The N-termini of these synthetically designed peptides are blocked with a tertiarybutyloxycarbonyl (Boc) group, and the C-termini are esterified. These peptides do not possess side chains that are capable of complexation and hence the backbone amide units are the sole sites of protonation and metallation. The cleavage patterns of the protonated peptides are strikingly different from those of sodium ion adducts. While the loss of the N-terminal blocking group occurs quite readily in the case of MS/MS of [M+Na]+, the cleavage of the C-terminal methoxy group seems to be a facile process in the case of MS/MS of [M+H]+. Fragmentation of the protonated adducts yields only bn ions, while yn and an ions are predominantly formed from the fragmentation of sodium ion adducts. The an ions arising from the fragmentation of [M+Na]+ lack the N-terminal Boc group (and are here termed an* ions). MS/MS of [M+Na]+ species also yields bn ions of substantially lower intensities that lack the N-terminal Boc group (bn*). A similar distinction between the fragmentation patterns of proton and sodium ion adducts is observed in the case of peptides possessing an N-terminal acetyl group. An example of the fragmentation of the H+ and Na+ adducts of a naturally occurring peptaibol from a Trichoderma species confirms that fragmentation of these two ionized species yields complementary information, useful in sequencing natural peptides. Inspection of the isotopic pattern of bn ions derived from [M+H]+ adducts of peptaibols provided insights into the sequences of microheterogeneous samples. This study reveals that the combined use of protonated and sodium ion adducts should prove useful in de novo sequencing of peptides, particularly of naturally occurring neutral peptides with modified N- and C-termini, for example, peptaibols. Copyright © 2006 John Wiley & Sons, Ltd. [source] Primary structural determination of N-terminally blocked peptides from the bark of Eucommia ulmoides Oliv by mass spectrometric analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2003Ren-Huai Huang Sequencing of N-terminally blocked proteins/peptides is a challenge since these molecules inhibit processing by Edman degradation. By using high accuracy Fourier transform ion cyclotron resonance (FTICR) tandem mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), the primary structures of two novel N-terminally blocked antifungal peptides (EAFP1 and EAFP2), purified from the bark of Eucommia ulmoides Oliv, have been determined. The results show that the high mass accuracy provided by FTICR mass spectrometry is effective to determine the N-terminally blocking group, and can simplify the task of spectral interpretation and improve the precision of sequence determination. The combination of MALDI-TOFMS with carboxyl peptidase Y digestion was used to determine the C-terminal 36- and 27-residue sequences of EAFP1 and EAFP2, respectively, to provide the sequence linkage information for tryptic fragments. Compared with traditional peptide chemistry the advantage of mass spectrometric techniques is their simplicity, speed and sensitivity. Copyright © 2003 John Wiley & Sons, Ltd. [source] Stereo- and Regioselectivity in an Intramolecular Nitrone,Alkene Cycloaddition of Hept-6-enoses with a trans -Acetonide Blocking GroupCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2009Abstract From sugar to cycloadduct: The effect of the trans -acetonide blocking group and the stereochemistry of the substituents on the regio- and stereoselectivity in the intramolecular nitrone,alkene cycloaddition (INAC) reaction of hept-6-enoses (see scheme) is reported and studied by using theoretical analysis. The positional effect of the trans -acetonide blocking group and the effect of the stereochemistry of the substituents on the regio- and stereoselectivity in intramolecular nitrone,alkene cycloaddition (INAC) reactions of hept-6-enoses are reported. Hept-6-enoses with a 2,3- trans -acetonide group were reacted with N -alkyl hydroxylamine to give a mixture of exo and endo cycloadducts (cyclohexanols and cycloheptanols, respectively). Complete formation of endo cycloadducts (cycloheptanols) was realized for the INAC reaction of hept-6-enoses containing a 3,4- trans - O -isopropylidene ring. Similarly, reaction of a hept-6-enose possessing a 4,5- trans -acetonide group surprisingly afforded exo cycloadducts (cyclohexanols) exclusively. The regio- and stereochemical outcomes of these reactions were rationalized on the basis of transition-state energies obtained by computation. [source] A New Efficient Route to Chiral 1,3-Disubstituted Ferrocenes: Application to the Syntheses of (Rp)- and (Sp)-17,-[(3,-formylferrocenyl)ethynyl]estradiolCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006Benoît Ferber Abstract Starting from (2S,4S)-2-ferrocenyl-4-(methoxymethyl)-1,3-dioxane (4), use of the stereogenic ortho -directing menthyl para- tolyl sulfoxide group, which occupies the 2, position in the ferrocenyl ring and redirects subsequent lithiation to the 3, position, allowed the synthesis of optically pure (Sp)-1-formyl-3-iodoferrocene (8), that was characterized by single-crystal X-ray diffraction. Combination of this method with a protection,deprotection strategy, using trimethylsilyl as a temporary blocking group, yielded (Rp)-1-formyl-3-iodoferrocene (13). Separate Sonogashira coupling of each of the enantiomeric iodoformylferrocenes 8 and 13 with 17,-ethynyl-estradiol produced (Rp)-17,-[(3,-formylferrocenyl)ethynyl]estradiol (14) and (Sp)-17,-[(3,-formylferrocenyl)ethynyl]estradiol (15), respectively. [source] | ||||||||||