Synthesis of Penicillin N and Isopenicillin N

Enantiomeric 2-(N-allyloxycarbonyl)aminoadipic acid 1-allyl esters were obtained from the corresponding 2-(N-trityl)aminoadipic acid diallyl esters following selective hydrolysis of the allyl 6-ester group and subsequent exchange of the trityl group by the allyloxycarbonyl function. The resulting monoacids were used to acylate 6-aminopenicillanic acid allyl ester using a carbodiimide-mediated coupling. The products, the l- and d-isomers of 6-[6-(2-(N-allyloxycarbonyl) aminoadipyl)]aminopenicillanic acid diallyl ester were deprotected in one step by catalytic allyl transfer using tetrakis-(triphenylphosphine)palladium(0), to afford isopenicillin N and penicillin N, respectively. The presented straightforward route to penicillin N and isopenicillin N is uniquely compatible with the sensitive nature of the condensation products and gives entry to a new and high yielding procedure that is superior to existing approaches.