An improved synthesis and in vitro activity of cephalosporins with a (4-carboxy-3-hydroxy-5-isothiazolyl)thiomethyl group at the 3-position and its application to the preparation of new derivatives are described. These compounds showed excellent activity against Gram-negative bacteria including β-lactamase producing strains. Among them, 2f was the most interesting because of its broad spectrum of antibacterial activity, including Gram-positive bacteria, and its outstanding inhibitory potency against Pseudomonas aeruginosa.
Carboxylate-stabilised sulfur ylides (thetin salts) in asymmetric epoxidation for the synthesis of glycidic acids. Mechanism and implications
作者:Varinder K. Aggarwal、Christina Hebach
DOI:10.1039/b418740g
日期:——
The reaction of carboxylate-stabilised sulfur ylides (thetinsalts) with aldehydes and ketones has been investigated. Using both achiral and chiral sulfur ylides, good yields were obtained with dimsylsodium or LHMDS as bases in DMSO or THF-DMSO mixtures. However, the enantioselectivities observed with a camphor-based sulfide were only moderate (up to 67%). The reaction was studied mechanistically by
Reactions of the α,β-unsaturated aldehyde 1 with the O-silyl ketene acetals 10 have been investigated. Both Michael addition and [4+2] cycloaddition products were formed, depending on the reaction conditions.