- (3: S,4 R)-3,4-Dihydroxy-N-Alkyl-l-homoprolines: Synthesis and computational mechanistic studies
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This is the first synthetic report of (3S,4R)-dihydroxy-N-Alkyl-l-homoprolines described so far. 2,4-O-Benzylidene-d-erythrose was obtained from d-glucose with an improved yield, and then transformed into the title (3S,4R)-dihydroxy-N-Alkyl-l-homoprolines, in a two-step strategy, with excellent overall yields. Hydrogenolysis of the benzyl group led to the NH congener. The synthesis of final products from 1,4-lactone intermediates was studied by computational means either under acidic or basic conditions. The theoretical mechanism studies fully explain the experimental results: (a) an equilibrium between l-homoprolines and their bicyclic counterparts is established in acids; (b) the equilibrium suffers a complete displacement towards the l-homoproline side in a basic medium.
- Freitas, David S.,Sousa, Cristina E. A.,Parente, Joana,Drogalin, Artem,Gil Fortes, António,Cerqueira, Nuno M.F.S.A.,Alves, Maria J.
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- Concise synthesis of enantiomers of 4-aminobutane-1,2,3-triol
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(Chemical Equation Presented) A very efficient synthesis of (2R,3S) and (2S,3R)-4-aminobutane-1,2,3-triol has been developed using either D- or L-glucose as the starting material. A key step is the one-pot conversion of an aldehyde to an amide, the scope of which has been extended to include other carbohydrate-derived aldehydes.
- Dunlap, Norma K.,Drake, John,Ward, Andrea,Salyard, Tracy L. J.,Martin, Leah
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p. 2928 - 2930
(2008/09/19)
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- Effects of α-alkoxy substitution and conformational constraints on 6-exo radical cyclizations of hydrazones via reversible thiyl and stannyl additions
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Access to multifunctional hydrazones of relevance to dysiherbaine synthesis studies is described. Subsequent radical cyclizations of multifunctional hydrazones via a Si- and C-linked tethering strategy are shown to function effectively in 6-exo fashion. C
- Friestad, Gregory K.,Mathies, Alex K.
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p. 9373 - 9381
(2008/02/10)
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- A new reaction manifold for the Barton radical intermediates: Synthesis of N-heterocyclic furanosides and pyranosides via the formation of the C1-C2 bond
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The first radical intermediate in the thiourethane-mediated deoxygenation of an alcohol (Barton-McCombie reaction) can participate in an exo-hex-5-enyl- or exo-hept-6-enyl-type radical cyclization when a suitable radical acceptor (e.g., α,β-unsaturated es
- Rhee, Jong Uk,Bliss, Brian I.,RajanBabu
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p. 1492 - 1493
(2007/10/03)
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- Stereochemical control in radical cyclization routes to N-glycosides: Role of protecting groups and of the configuration (E versus Z) of the acceptors
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The first radical intermediate in the thiourethane-mediated deoxygenation of an alcohol (Barton-McCombie reaction) can participate in an exo-hex-5-enyl or exo-hept-6-enyl type radical cyclization when a suitable radical acceptor (e.g. α,β-unsaturated este
- Rhee, Jong Uk,Bliss, Brian I.,RajanBabu
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p. 2939 - 2959
(2007/10/03)
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- Stereochemical models for the enantiocontrolled construction of fully functionalized C rings via intramolecular aldolization in advanced precursors to paclitaxel
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Six transition-state models for intramolecular aldol C-ring annulation in suitably substituted bicyclo-[6.2.1]undecanones have been defined. The first consideration is the inherent conformational flexibility of the nine- membered ketonic ring which does not limit effective deprotonation to a single C-8 epimer. When the oxygen substituents at C-4 and C-5 are not covalently linked, the configuration at C-5 defines the stereochemical course of the ring closure, with only the β series being amenable to the proper elaboration of paclitaxel. When C-4 and C-5 are incorporated into a 1,3- dioxane ring instead, the principal stereocontrol element is translocated into the aryl-substituted carbon of the cyclic acetal. To the extent that the Ar group remains equatorially disposed, then proper aldolization will materialize in only one of the four possible diastereomers. Experimental tests that are provided for three of the models are shown to conform to expectations. This analysis of the origin of stereoselectivity has, for the first time, defined the scope and limitations associated with C-ring closure by means of the aldol protocol.
- Paquette, Leo A.,Zeng, Qingbei,Tsui, Hon-Chung,Johnston, Jeffrey N.
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p. 8491 - 8509
(2007/10/03)
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- Enantiospecific Synthesis of Sphingosine and Ceramide Stereoisomers with 3S Configuration from D-Glucose
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Utilizing the carbon framework (C3-C6) and chirality (at C4 and C5) of D-glucose, (2S,3S,4E and 2R,3S,4E)-2-amino-4-octadecene-1,3-diol (sphingosine analogues) and four stereoisomers (2S,3S,4E-,2S,3S,4Z-,2R,3S,4E-,and 2R,3S,4Z-) of the ceramide derivatives were synthesized in a stereocontrolled way.
- Fujita, Shuji,Sugimoto, Mamoru,Tomita, Kenkichi,Nakahara, Yoshiaki,Ogawa, Tomoya
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p. 2561 - 2570
(2007/10/02)
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