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The Hofmann-Loeffler-Freytag reaction, carried out by irradiation in sulphuric acid of N-chloro-l-amino-acids 3a-d, gives δ-chlorinated compounds which can be cyclized to l-prolines 4a-e. This convenient synthesis does not affect the asymmetric centres of
- Titouani, S.Lafquih,Lavergne,Viallefont,Jacquier
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- Trichodestruxins A-D: Cytotoxic Cyclodepsipeptides from the Endophytic Fungus Trichoderma harzianum
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Four new cyclodepsipeptides, trichodestruxins A-D (1-4), together with destruxin E2 chlorohydrin (5) and destruxin A2 (6), were isolated from the plant endophytic fungus Trichoderma harzianum by a bioassay-guided fractionation method. Their planar structures were elucidated on the basis of 1D and 2D NMR and MS/MS spectroscopic analyses. The stereochemical configuration was established by application of the advanced Marfey's method, J-based configuration analysis, Mosher's method, and chemical derivatizations. Trichodestruxin B contains hydroxy acid fragments of the THPA unit, while trichodestruxins A and C contain the β-methylproline moiety. All cyclodepsipeptides displayed cytotoxicity against HT-29, A549, and/or P388 cell lines with IC50 values of 0.7-19.1 μM.
- Liu, Zhiguo,Sun, Yi,Tang, Mengyue,Sun, Peng,Wang, Anqi,Hao, Yanqi,Wang, Yanan,Pei, Yuehu
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- Efficient chemoenzymatic synthesis of (2S,3R)-3-hydroxy-3-methylproline, a key fragment in polyoxypeptin A and FR225659
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We report an efficient synthesis of protected (2S,3R)-3-hydroxy-3-methylproline that proceeds in three steps with complete stereoselectivity. This route represents a significant improvement over previous approaches to this noncanonical amino acid. Key to this success is the development of a one-pot chemoenzymatic procedure for the preparation of (2S,3S)-3-methylproline from L-isoleucine. This work lays the foundation for future chemoenzymatic syntheses of polyoxypeptin A and FR225659.
- Zhang, Xiao,Renata, Hans
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- Scytalidamides A and B, New Cytotoxic Cyclic Heptapeptides from a Marine Fungus of the Genus Scytalidium
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Two new cyclic heptapeptides have been isolated from the culture broth of a marine fungus, Scytalidium sp., collected from the Bahamas. The planar structures of scytalidamides A (1) and B (2) were assigned on the basis of 1D and 2D NMR spectroscopic techniques, while the absolute configuration of the amino acid residues in both molecules was determined by application of the advanced Marfey's method. The absolute stereochemistry of the uncommon 3-methylproline moiety in scytalidamide B (2) was confirmed by isolation and CD measurements, as well as application of the advanced Marfey's method. Scytalidamides A (1) and B (2) showed moderate in vitro cytotoxicity toward HCT-116 human colon adenocarcinoma with IC50 values of 2.7 and 11.0 μM, respectively.
- Tan, Lik Tong,Cheng, Xing C.,Jensen, Paul R.,Fenical, William
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- Synthesis of non-proteinogenic amino acids using Michael addition to unsaturated orthopyroglutamate derivative
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Stereoselective synthesis of non-proteinogenic amino acids via Michael addition to 3,4-didehydropyroglutamate derivative in which the carboxyl function is protected as a 2,7,8-trioxabicyclo[3.2.1]octane (ABO ester) group is described. The obtained 3-subst
- Oba, Makoto,Saegusa, Tsuneki,Nishiyama, Naohiro,Nishiyama, Kozaburo
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experimental part
p. 128 - 133
(2009/04/06)
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- Synthesis of Homochiral 3-Substituted Glutamic Acids and Prolines from Pyroglutamic Acid
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Efficient syntheses of (2S,3S)-methylproline (5a) and (2S,3R)-phenylproline (5b) are described, starting from the readily available pyroglutaminol derivatives 2a and 2b via conjugate 1,4=addition of organocuprates to 1.Catalytic hydrogenation of 3 from th
- Herdeis, Claus,Hubmann, Hans Peter,Lotter, Hermann
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p. 351 - 354
(2007/10/02)
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- 2-Amino Ketene S,S-Acetals as α-Amino Acid Homoenolate Equivalents. Synthesis of 3-Substituted Prolines and Molecular Structure of 2-(N-Pivaloylpyrrolidin-2-ylidene)-1,3-dithiane
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Allylic deprotonation of the heterocyclic 2-amino ketene S,S-acetal 8a, followed by regioselective γ-alkylation reaction of the resulting organolithium 10 (a proline homoenolate equivalent) with electrophiles, leads to adduct 11.Controlled hydrolytic cleavage of 11 gives a series of 3-substituted prolines, including the conformationally-constrained aspartate and glutamate derivatives, 14e and 14f respectively.The bicyclic thiolactam 18 has been prepared in an attempt to provide an asymmetric variant of organolithium 10 but efforts to generate the requisite ketene N,S-acetal 19 were unsuccessful.Extension of the ketene S,S-acetal chemistry to other ring sizes has been examined within the context of substituted azetidine-2-carboxylates.Condensation of the protected amino ester 20 with AlMe3-HS(CH2)3SH was complicated, however, by the reactivity of the four-membered ring and led to the ring-opened adduct 24, with none of the required ketene S,S-acetal 22 being observed.
- Moss, William O.,Jones, Annette C.,Wisedale, Richard,Mahon, Mary F.,Molloy, Kieran C.,et al.
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p. 2615 - 2624
(2007/10/02)
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- Highly Diasteroselective Michael-Addition of Lithiated Camphor Imines of Glycine Esters to α,β-Unsaturated Esters. Synthesis of Optically Pure 5-Oxo-2,4-pyrrolidinedicarboxylates of Unnatural Stereochemistry
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The lithium enolates of camphor imines of glycine esters underwent highly diastereoselective Michael additions to the α,β-unsaturated esters.The tightly chelated structure of the Z,E enolates and the selective approach of the α,β-unsaturated esters to the
- Kanemasa, Shuji,Tatsukawa, Akira,Wada, Eiji
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p. 2875 - 2883
(2007/10/02)
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- Generation of α-amino acid homoenolate equivalents. Synthesis of 3-substituted prolines
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Deprotonation of the N-protected aminoketene-S,S-acetal (6) and reaction of allylic anion (7) with electrophiles leads to adducts (8) which have been converted to 3-substituted prolines (11). Conformationally constrained variants (11d) and (11e) of aspartic and glutamic acid have been prepared.
- Moss, William O.,Bradbury, Roben H.,Hales, Neil J.,Gallagher, Timothy
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p. 5653 - 5656
(2007/10/02)
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- Synthesis of Enantio- and Diastereoiso-merically Pure Substituted Prolines via Condensation of Glycine with Olefins Activated by a Carbonyl Group
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The glycine fragment in the nickel(II) complex (1) formed from the Schiff's base of glycine and (S)-o-benzophenone (2) undergoes base-catalysed Michael addition to acrylaldehyde, α-methylacrylaldehyde, (E)-crotonaldehyde, (E)-cinnamaldehyde, and methyl vinyl ketone.No products of 1,2-addition were found in the Et3N-catalysed reactions.Addition followed by epimerization of the isomeric complexes proceeds with high diastereoselectivity at Cα (90percent) and Cβ of the corresponding amino acid side chains.After chromatographic separation, the diastereoisomerically pure complexes were decomposed and the resulting dihydropyrrole-2-carboxylic acids reduced with NaBH3CN to give (S)-proline, trans-3-methyl-(S)-proline, trans-5-phenyl-(S)-proline, and a mixture of cis- and trans-5-methyl-(S)-prolines.The chiral auxiliary (2) was recovered in 80-90percent yield.
- Belokon', Yuri N.,Bulychev, Aleksandr G.,Pavlov, Viacheslav A.,Fedorova, Eugenia B.,Tsyryapkin, Vladimir A.,et al.
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p. 2075 - 2084
(2007/10/02)
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