Direct1H n.m.r. observation of the cell-free conversion of δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine and δ-(L-α-aminoadipyl)-L-cysteinyl-D-(–)-isoleucine into penicillins

The cell-free conversion of δ-(L-aminoadipyl)-L-cysteinyl-D-(–)-isoleucine (lb) into a penicillin (2b) was observed directly by 1H n.m.r. spectroscopy and the thiazolidine ring formation was shown to occur with retention of stereochemistry at C-3 of the isoleucinyl residue by 1H nuclear Overhauser enhancement studies of the product penicillin in the deproteinated incubation mixture.