Sample retention, closure

Hb = H, which underwent Curtius rearrangement with retention of configuration at the labeled carbon followed by deprotection to give the labeled samples of isoserine 85. Esterification, N tritylation, O tosylation, and ring closure then led to the labeled aziridines 86 which underwent ring opening and deprotection in perchloric acid to yield 2R, 3R)-[2,3- H2]- and 2R, 3S)-[3- H,]serines 60f, Ha = H, and 60f, Hb = H, respectively (94). 

In our work (133, 134) and that of Aberhart etal. (135) and Baldwin et al. (136), the samples of cysteine were used to examine the biosynthesis of the -lactam antibiotic penicillin 142. All three groups found that the ring closure step that gave rise to the j -lactam in the antibiotic occurred with retention of configuration (Scheme 44). We have also shown (137) that the... 

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