- Effects of pH on aggregation and photodynamic activities of cationic zinc phthalocyanines substituted with amides
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This work reports on the effects of pH (especially base addition) on the properties of two cationic phthalocyanines substituted with amide groups. The absorption spectra, photo-stability, singlet oxygen generation ability and photodegradation of CT DNA of
- Wang, Ao,Chen, Xianglan,Zhang, Liu,Zhang, Guangyi,Zhou, Lin,Lu, Shan,Zhou, Jiahong,Wei, Shaohua
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- Interstrand Aminoacyl Transfer in a tRNA Acceptor Stem-Overhang Mimic
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Protein-catalyzed aminoacylation of the 3′-overhang of tRNA by an aminoacyl-adenylate could not have taken place prior to the advent of genetically coded peptide synthesis, and yet the latter process has an absolute requirement for aminoacyl-tRNA. There must therefore have been an earlier nonprotein-catalyzed means of generating aminoacyl-tRNA. Here, we demonstrate efficient interstrand aminoacyl transfer from an aminoacyl phosphate mixed anhydride at the 5′-terminus of a tRNA acceptor stem mimic to the 2′,3′-diol terminus of a short 3′-overhang. With certain five-base 3′-overhangs, the transfer of an alanyl residue is highly stereoselective with the l-enantiomer being favored to the extent of ~10:1 over the d-enantiomer and is much more efficient than the transfer of a glycyl residue. N-Acyl-aminoacyl residues are similarly transferred from a mixed anhydride with the 5′-phosphate to the 2′,3′-diol but with a different dependence of efficiency and stereoselectivity on the 3′-overhang length and sequence. Given a prebiotically plausible and compatible synthesis of aminoacyl phosphate mixed anhydrides, these results suggest that RNA molecules with acceptor stem termini resembling modern tRNAs could have been spontaneously aminoacylated, in a stereoselective and chemoselective manner, at their 2′,3′-diol termini prior to the onset of protein-catalyzed aminoacylation.
- Bjork, Samuel J.,Liu, Ziwei,Su, Meng,Sutherland, John D.,Wu, Long-Fei
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supporting information
p. 11836 - 11842
(2021/08/03)
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- Highly stereoselective syntheses of syn- and anti-1,2-amino alcohols
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The reduction of N-protected amino ketones can be carried stereoselectively to produce either the syn- or anti-amino alcohol diastereomer. Carbamate-protected amino ketones can be reduced predictably and selectively to anti-amino alcohols with LiAlH(O-t-Bu)3 in ethanol at -78°C. N-Trityl-protected amino ketones can be reduced selectively to syn-amino alcohols with LiAlH(O-t-Bu)3 in THF at -5°C.
- Hoffman, Robert V.,Maslouh, Najib,Cervantes-Lee, Francisco
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p. 1045 - 1056
(2007/10/03)
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- Stabilized analogs of thymopentin. 1. 4,5-Ketomethylene pseudopeptides
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The pentapeptide, thymopentin (Arg1-Lys2-Asp3-Val4-Tyr5) is known for its activity as an immunomodulating drug, but with limited half-life in plasma. In this first paper of a series of three studies, the synthesis of analogs stabilized at the peptide bond between the C-terminal amino acids via insertion of a ketomethylene moiety is described. N-Blocked pseudopeptides containing Val(k)Phe, Ala(k)Phe, and Val(k)Val units were prepared and attached to chloromethyl Merrifield resin via the carboxy terminal. Removal of the N-BOC group by trifluoroacetic acid was followed by sequential coupling with N-BOC dipeptides of aspartic acid to yield resin-bound N-BOC pseudotetrapeptides. Removal of N-BOC and coupling with N-BOC-r-N- tosylarginine followed by total cleavage of blocking groups and resin by HF afforded the target pseudopentapeptides. The analogs were found to compete favorably with thymopentin for binding to CEM cells, but binding was reduced by about 20-30% on average. All analogs showed significant enhancement of half-life versus thymopentin in mouse serum, but most showed only modest improvement in human serum. Insertion of proline or norleucine at position 2 in the chain caused a substantial increase in half-life (3-4-fold), while N- methylnorleucine conferred complete stability in the analogs.
- DeGraw, Joseph I.,Almquist, Ronald G.,Hiebert, Charles K.,Colwell, William T.,Crase, Jac,Hayano, Takeshi,Judd, Amrit K.,Dousman, Linda,Smith, R. Lane,Waud, William R.,Uchida, Itsuo
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p. 2386 - 2397
(2007/10/03)
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- Efficient Synthesis of N-Triphenylmethyl α-Amino Acids
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A new one-pot synthesis of N-triphenylmethyl(trityl) α-amino acids 3 via their trityl ester 2 has been developed.
- Mutter, Manfred,Hersperger, Rene
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p. 198 - 200
(2007/10/02)
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- Efficient "One-Pot" Synthesis of N-Trityl Amino Acids
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A sequential procedure has been developed whereby neutral amino acids 1 were tritylated via their corresponding trimethylsilyl esters 2 to afford, after mild hydrolysis, N-trityl amino acids 3 in high yields and purity.Hydroxy amino acids 4 were preferent
- Barlos, Kleomenis,Papaioannou, Dionysios,Theodoropoulos, Dimitrios
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p. 1324 - 1326
(2007/10/02)
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