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Naturally occurring carbapenem antibiotics having a double bond in the side chain, when refluxed in chloroform containing quarternary alkylammonium halides, were converted into Z isomers in high yields. The mechanism of this new equilibration involves intramolecular proton transfer from the carboxylic acid to the carbon alpha to the sulfur atom in the side chain as shown by deuterium-labeling experiments. Some Z isomers showed stronger protective effects in mice infected by Escherichia coli O-111 and more potent synergistic activities with cefotiam in mice infected by Proteus vulgaris GN4815 than did the naturally occurring E isomers. The decomposition rates of the Z isomers in mouse kidney homogenates were about 3-fold slower than those of the E isomers.

Emericedins A, B, and C, new betaines having inhibitory activity of long chain fatty acid oxidation, were isolated from the culture broth of Emericella quadrilineata IFO 5859. Their structures were determined by spectroscopic analyses as (R)-3-(acylamino)-4-(trimethylammonio)butyrate (acyl: A, acetyl; B, propionyl; C, n-butyryl). Structural confirmation and assignment of absolute configuration were made by chemical synthesis from L-asparagine. Deacylation of emericedin gave a potent derivative, (R)-3-amino-4-(trimethylammonio)butyrate, designated as emeriamine. In order to study the structure-activity relations, various analogues of emeriamine, including a stereoisomer, were prepared. Among them, N-palmitoyl and N-myristoyl derivatives showed much stronger inhibition of fatty acid oxidation than emeriamine.