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Kita, Yasuyuk,Shibata, Norio,Kawano, Noriyuki,Tohjo, Takashi,Fujimori, Chino,Ohishi, Hirofumi 梨花女子大學校 藥學硏究所 1994 藥學硏究論文集 Vol.- No.4
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.