- Stereo- and Enantio-controlled Synthesis of Chiral Intermediates for the Total Synthesis of Thienamycin and Related β-Lactam Antibiotics from 3-Hydroxybutyrates
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The synthesis of (1'R,3S,4S)- and (1'R,3S,4R)-3-(1'-t-butyldimethylsilyloxyethyl)-4-hydroxymethyl-2-azetidinone from ethyl (S)-3-hydroxybutyrate is reported.
- Georg, Gunda I.,Gill, Harpal S.
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- Enantioselective lipase-catalyzed acetylation of β-lactam precursors of carbapenem antibiotics
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The Amano PS-lipase-catalyzed enantioselective acetylation in vinyl acetate of (±)-3-hydroxyethyl-β-lactams 3-6, useful precursors of carbapenem antibiotics, proceeds with high enantioselectivity (E > 98) to afford the corresponding acetates 3b-6b in optically pure form. The rate of acetylation is influenced by the relative stereochemistry of the C(3)-C(4) β-lactam carbon atoms, the trans isomers being transformed much faster than the cis ones. The stereochemical preference of the lipase-PS is for the (1′R,3R) enantiomers, as determined by chemical correlation. On the other hand, the lipase-PS-catalyzed hydrolysis of esters 3b,d in phosphate buffer proceeds with low selectivity and at a lower rate.
- Bucciarelli, Maria,Davoli, Paolo,Forni, Arrigo,Moretti, Irene,Prati, Fabio
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p. 2489 - 2494
(2007/10/03)
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- Synthesis of β-lactams by condensation of titanium enolates of 2-pyridylthioesters with imines. Influence of the imine structure on the trans/cis stereoselectivity
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The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords β-lactams in trans/cis ratios that largely depend on the structure of the C-imine residue. Bulky and non-chelating heteroatom-containing groups lead to the formation of trans β-lactams, while sterically non-requiring or chelating groups favour the formation of the cis-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.
- Annunziata, Rita,Benaglia, Maurizio,Cinquini, Mauro,Cozzi, Franco,Ponzini, Francesco,Raimondi, Laura
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p. 2939 - 2948
(2007/10/02)
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- Asymmetric Synthesis of (1'R,3R,4R)-4-Acetoxy-3(1'-((tert-butyldimethylsilyl)oxy)ethyl)-2-azetidinone and Other 3-(1'-Hydroxyethyl)-2-azetidinones from (S)-(+)-Ethyl 3-Hydroxybutanoate: Formal Total Synthesis of (+)-Thienamycin
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The synthesis of (1'R,3R,4R)-4-acetoxy-3-(1'-((tert-butyldimethylsilyl)oxy)ethyl)-2-azetidinone, an important precursor for synthesis of carbapenems and penems, is detailed.The methodology utilized relies on the addition, cyclization reaction between the dianion of (S)-(+)-ethyl 3-hydroxybutanoate and N-arylaldimines.The syntheses of other useful optically active 3-(hydroxyethyl)-2-azetidinones are presented.A study of factors influencing the stereochemistry in the addition, cyclization reaction for the formation of 3-(1'-hydroxyethyl)-2-azetidinones is detailed.
- Georg, Gunda I.,Kant, Joydeep,Gill, Harpal S.
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p. 1129 - 1135
(2007/10/02)
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- 3-(1'-hydroxyethyl)-2-azetidinones from 3-hydroxybutyrates and N-arylaldimines
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Dianion imine addition, cyclisation reaction between ethyl-3-hydroxybutyrate and the aldimines generates β-lactams with the hydroxyethyl side chain of thienamycin and related β-lactam antibiotics in place. The effects of the N-arylaldimine and the reactio
- Georg,Gill,Gerhardt
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p. 3903 - 3906
(2007/10/02)
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