- Soluble-polymer-supported synthesis of β-lactams on a modified poly(ethylene glycol)
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A modified poly(ethylene glycol) (PEG) has been developed for the soluble-polymer-supported synthesis of β-lactams. The monomethylether of PEG (MeOPEG) with an average Mw of 5000 was used as the support, a 4-(3-propyl)phenyl residue as the spacer, and a 4-oxyphenylamino group as the moiety with the reactive functionality. From this modified PEG representative aromatic, heteroaromatic, unsaturated, and aliphatic imines were obtained in high yields by different procedures. The polymer-supported imines were then employed to prepare several β-lactams by enolate/imine condensation and ketene/ imine cycloaddition. Examples of the control of the absolute stereochemistry during the azetidinone ring formation are also reported. The reactions carried out on the polymer-bound imines showed a remarkable similarity to those performed on nonimmobilized imines, both in terms of yields and stereoselectivities. Removal of the β-lactams from the polymer has also been accomplished to directly deliver the N-unsubstituted azetidinones.
- Annunziata, Rita,Benaglia, Maurizio,Cinquini, Mauro,Cozzi, Franco
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p. 133 - 138
(2007/10/03)
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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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- ANODIC N-DEARYLATION OF 2-AZETIDINONES
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N-Methoxyphenyl-2-azetidinones are dearylated under mild conditions via anodic oxidation
- Corley, Edward G.,Karady, Sandor,Abramson, Newton L.
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p. 1497 - 1500
(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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- 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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p. 1433 - 1435
(2007/10/02)
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