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KMID : 0617319940040010129
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Journal of Pharmacetical Sceiences Ewha Womans University
1994 Volume.4 No. 1 p.129 ~ p.134
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Pummerer-type Cyclization of Arnstein Tripeptide Analogues Induced by O-Silylated Ketene Acetals
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Kita, Yasuyuk
Shibata, Norio/Kawano, Noriyuki/Tohjo, Takashi/Fujimori, Chino/Ohishi, Hirofumi
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Abstract
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We report the first biomimetic conversion of Arnstein tripeptide analogues (1a and 1b) into cis, ß-lactams (2a and 2b) using O-silylated ketene acetal (3) involving asymmetric induction from the sulfoxide sulfur to the α-carbon. The peptide 1 was treated with 3 at room temperature in the presence of a catalytic amount of ZnI_2, in MeCN to give cis-2, trans-2, and α-siloxysulfide (7). Reaction of R-1 with 3 gave cis-2 predominantly, and S-1 gave a mixture of cis-2 and trans-2. High cis selectivity was obtained by the use of a large volume of solvent and was strongly influenced by the absolute stereochemistry of the sulfaxide, the cysteinylamino group, and the volume of solvent. The cis ß-lactams (2a,b) were obtained preferentially from R-la,b. These chemical transformations strongly support Baldwin´s mechanism which involves the initial formation of the cis ß-lactam by the Pummerer-type cyclization of the Arnstein tripeptide in penicillin biosynthesis and provide useful information on the first key step in penicillin biosynthesis.
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