31P NMR of native high molecular weight DNA shows that the phosphodiester backbone undergoes reorientation with a rotational correlation time of about 2 X 10(-6) s at 30 degrees C. This rate is consistent with the flexibility of the polymer and does not require the presence of internal phosphate motions. The line width of the phosphorus resonance of DNA is due to incompletely averaged 31P-1H dipolar couplings and 31P chemical shift anisotropy relaxation; high-power proton decoupling and magnetic field dependence experiments separate the two effects and allow the use of the line width for determination of the rotational correlation time. The line width is dependent on temperature, and an activation energy of 5-8 kcal/mol is calculated for the motion of DNA.
. Can. J. Chem. 64, 1590 (1986). Alternaria molds produce numerous mycotoxins including many a-dibenzopyrones such as alternariol (AOH) and related polyketides. AOH, presumed to be the initial a-dibenzopyrone produced, has for 20 years been considered to be biosynthesized from a single polyketide chain in a single step reaction. The present study presents evidence that the reaction may proceed through an intermediate, norlichexanthone (NLX). Bond cleavage and rearrangement of NLX to form AOH may be similar to aflatoxin B1 formation from sterigmatocystin. The 2-D INADEQUATE experiment was used to assign the I3c spectrum of AOH and to distinguish between possible mechanisms by which AOH may be synthesized from 1-13C and 2-I3C acetates via NLX.E. E. STINSON, W. B. WISE, R. A. MOREAU, A. J. JUREWCZ et P. E. PFEFFER. Can. J. Chem. 64, 1590 (1986). Les moisissures Alternaria produisent diverses mycotoxines, y compris plusieurs a-dibenzopyrones, comme l'alternariol (AOH) et des polycktides apparent&. I1 est supposC que le AOH est l'a-dibanzopyrone qui est produite initialement et, depuis plus de 20 ans, on a considkrk que ce composC est produit par une biosynthkse impliquant une seule chaine polycCtide rtagissant au cours d'une seule rkaction. Dans le present travail, on prksente des donnkes suggCrant que le rkaction procMe peut-Stre par le biais d'un intermkdiaire, la norlichexanthone (NLX). I1 est possible que le bris de la liaison et la transposition de la NLX pour former le AOH se produisent d'une faqon semblable h ce qui se produit lors de la formation de l'aflotoxine B1 B partir de la stkrigmatocystine. On a fait appel B des expkriences de 2-D INADEQUATE pour attribuer le spectre rmn du 13C du AOH et pour distinguer entre les mkcanismes possibles pour la synthkse du AOH B partir d'acktates marquCs au 13c dans les positions 1 et 2 et par le biais de la NLX.[Traduit par la revue]The Alternaria, a group of molds frequently involved in food
The transport and reactivity of oligonucleotides may be altered by attaching pendant peptides, and it is of interest to develop general synthetic methods for such bioconjugates. Two protecting group strategies are described for the synthesis of nucleotide peptides containing a lysine residue. The preparation of a lysine-nucleopeptide phosphoramidite reagent is described, along with its use in solid-phase DNA synthesis. Diand trinucleotides were prepared with pendant and extensively characterized by NMR. These studies showed the peptide side chains to have survived DNA synthesis conditions; we then incorporated nucleopeptide residues into longer oligonucleotides. A similar approach is described for the preparation of oligonucleotide histidines. Previously reported histidine-nucleopeptides serve as precursors to phosphoramidites and to phosphodiester DNA building blocks. Both solutionand solid-phase techniques are presented for the preparation of histidine-containing oligonucleotides. The methodology developed here allows the incorporation of nucleopeptide residues at internal positions in a DNA sequence, using standard reagents. We present a complete description of the synthesis, purification, and characterization (via mass spectral and NMR methods) of the novel compounds.
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