Hatanaka, Ishimaru of 45% based on the initial glycine incorporation on the resin (this yield is higher than any previously obtained in these laboratories and, as mentioned above, results from thorough washings of the AG 3-x4 resin): [ ]22•0 -78.0 (c 0.5, 1 N AcOH). This material was shown to be homogeneous by tic, Rf 0.22 (BAW), and by paper electrophoresis. Only one spot in the direction of the cathode was observed in each of the buffer systems A and B.

A stereocontrolled synthesis of optically active 2-isocephem and 2-iso-oxacephem nuclei is described starting from L-aspartic acid.2-Isocephems and 2-iso-oxacephems have been reported to have potent antibacterial activity.l.2 However, most previous syntheses have led to racemic compounds and could not give optically active derivatives without resolution.2cJ Herein we report a stereocontrolled synthesis of optically active 2-isocephalosporin (1) and its oxa analogue (2) starting from L-aspartic acid. The key step is the stereoselective introduction of the azide group into L-aspartic acid leading to the amino acid ( 6 ) , which can be converted via a four-component condensation into chiral cis-3-azidoazetidinones.

A short and high-yielding synthesis of optically active 3-aminonocardicinic acid (3-ANA) is described. The fourth component condensation reaction of N2-protected l-2,3-diaminopropanoic acid with p-benzyloxybenzaldehyde and butyl isocyanide gave directly the amide derivatives of 3-ANA, as a diastereomeric mixture, which was, after conversion of the amide group into the benzhydryl ester, led in good yield to a single disatereomer with natural chirality via epimerization. Deprotection of the 3-ANA derivative gave 3-ANA.

Aus den Acetyl‐thiophenen (I) entstehen mit Selendioxid die Ketosäuren (IIa), deren Oxime (IIb) mit Na‐Hg zu den Aminen (III) reduziert werden können.

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