Penicillin sulphoxides epimerization

Parr method 995 Pauling s electronegativities 561 Penicillin sulphoxides epimerization of 750 synthesis of 246 Peptides 854, 864-866... 

The base-catalysed epimerization of penicillins and their sulphoxides has been described recently. Epimerization of penicillin sulphoxides (23) in the presence of l,5-diazabicyclo[4,3,0]non-5-ene ( DBN ) is attended by the production of the isothiazolone (24), presupposing the occurrence of j3-elimination. The possible... 

Epimerization of the penicillin sulphoxide (48 c,x) with diazabicyclononene leads rapidly to a 2 3 mixture of (48) and 6-epi-(48). However, p-nitrobenzyl ester (48 c,R = CH2C6H1NO2-4) under identical conditions gave a 6 4 1 mixture... 

NHj) without epimerization at C(6). The failure of penicillins bearing 6j8-secondary amide side-chains to undergo base-catalysed epimerization at C(6) was overcome if the amide function was first silylated, and the sulphoxides derived from the 6a-isomers were converted into CXl)-epi-cephem derivatives by acid-catalysed ring-expansion. ... 

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