- Organocatalyzed Asymmetric Aldol Reaction of α-Keto Amides with A Tripeptide Catalyst
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An organocatalyzed asymmetric aldol reaction of α-keto amides was developed. An N-terminal 4- trans -siloxyproline-based tripeptide with an l - tert -leucine unit adjacent to the 4- trans -siloxyproline residue was used to catalyze the reaction between various α-keto amides and acetone, to produce the corresponding aldol adducts with up to 99% yield and 91% ee.
- Kon, Kazumasa,Takai, Hiromu,Kobayashi, Takumu,Kohari, Yoshihito,Murata, Miki
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p. 829 - 832
(2021/02/26)
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- Unnatural tripeptide as highly enantioselective organocatalyst for asymmetric aldol reaction of isatins
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The development of unnatural tripeptides as highly enantioselective organocatalysts for the asymmetric aldol reaction of isatins was achieved. H-Pro-Gly-D-Ala-OH with the D-alanine residue as the C-terminal amino acid residue expressed the best enantioselectivity. The H-Pro-Gly-D-Ala-OH-catalyzed reaction of isatins gave various aldol adducts with up to 93% yield and up to 97% ee. Investigation of the transition state via DFT calculation revealed that high optical purity was realized by the D-alanine controlled steric environment.
- Kon, Kazumasa,Kohari, Yoshihito,Murata, Miki
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p. 415 - 418
(2019/01/05)
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- One-step C-terminal deprotection and activation of peptides with peptide amidase from stenotrophomonas maltophilia in neat organic solvent
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Chemoenzymatic peptide synthesis is a rapidly developing technology for cost effective peptide production on a large scale. As an alternative to the traditional C→N strategy, which employs expensive N-protected building blocks in each step, we have investigated an N→C extension route that is based on activation of a peptide C-terminal amide protecting group to the corresponding methyl ester. We found that this conversion is efficiently catalysed by Stenotrophomonas maltophilia peptide amidase in neat organic media. The system excludes the possibility of internal peptide cleavage as the enzyme lacks intrinsic protease activity. The produced peptide methyl ester was used for peptide chain extension in a kinetically controlled reaction by a thermostable protease.
- Arif, Muhammad I.,Toplak, Ana,Szymanski, Wiktor,Feringa, Ben L.,Nuijens, Timo,Quaedflieg, Peter J. L. M.,Wu, Bian,Janssen, Dick B.
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p. 2197 - 2202
(2014/07/21)
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- Synthesis of proline-derived dipeptides and their catalytic enantioselective direct aldol reactions: Catalyst, solvent, additive and temperature effects
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A series of dipeptides of l-proline-l-amino acid and l-proline-d-amino acid were synthesized to evaluate the catalytic effect for asymmetric direct aldol reactions. In the direct aldol reaction, a catalyst of l-proline-l-amino acid achieves better enantioselectivity than the corresponding l-proline-d-amino acid catalyst. Solubility of the dipeptide catalysts in the solvents is a key point for achieving a better yield of the direct aldol reaction, while hydrogen bonding of solvent does not play an important role in attaining better enantioselectivity and yield. Yield and enantioselectivity of the direct aldol reaction in water were improved by NMM and SDS additives, but the results that were done in plain DMSO were even better.
- Chen,Sung,Sung, Kuangsen
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experimental part
p. 839 - 845
(2010/08/06)
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- Synthesis and in vitro evaluation of macromolecular antitumour derivatives based on phenylenediamine mustard
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Poly-[N-(2-hydroxyethyl)-l-glutamine] (PHEG) and poly(ethylene glycol) (PEG)-grafted PHEG conjugates of N,N-di(2-chloroethyl)-4-phenylenediamine mustard (PDM) were synthetised. A collagenase-sensitive oligopeptide spacer was selected to link the cytotoxic agent PDM onto the polymeric carrier. First, the oligopeptide-drug conjugate, l-pro-l-leu-gly-l-pro-gly-PDM, was prepared. In a second step, the low molecular weight PDM derivative and PEG-NH2 were coupled to a N,N-disuccinimidylcarbonate activated PHEG. Dynamic laser light scattering measurements indicated the formation of aggregates. The presence of human serum albumin had no significant effect on the diameter of the conjugates. The hydrolytic stability of the conjugates was investigated in buffer solutions. The conjugates showed an improved stability compared to the parent nitrogen mustard. The enzymatic degradation studies of the polymeric conjugates were performed in the presence of collagenase type IV (Clostridiopeptidase A; EC 3.4.24.3), cathepsin B (EC 3.4.22.1), cathepsin D (EC 3.4.23.5) and tritosomes. Only the bacterial collagenase type IV was able to cleave the spacer releasing free PDM and its peptidyl derivative, gly-l-pro-gly-PDM. The in vitro cytotoxicity of the conjugates was evaluated against HT1080 fibrosarcoma cells and MDA adenocarcinoma cells. All conjugates showed low toxicity towards these cell lines.
- De Winne, Katleen,Seymour, Leonard W.,Schacht, Etienne H.
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p. 159 - 168
(2007/10/03)
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- STUDIES OF BITTER PEPTIDES FROM CASEIN HYDROLYZATE - VII. BITTERNESS OF THE RETRO-BPIa (VAL-ILE-PHE-PRO-PRO-GLY-ARG) AND ITS FRAGMENTS.
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To explain the bitter taste exhibited by BPIa (Arg-Gly-Pro-Pro-Phe-Ile-Val) which was isolated from casein hydrolyzate, the authors propose the following requirement: its characteristic spatial structure: the basic moiety in the N-terminal and the hydroph
- Shigenaga,Otagiri,Kanehisa,Okai
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p. 103 - 107
(2007/10/02)
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