Stereoselective Synthesis of Protected l - Allo -Enduracididine and l -Enduracididine via Asymmetric Nitroaldol Reaction

The diastereoselecetive and scalable synthesis of cyclic guanidine-containing nonproteinoginic amino acids, enduracididines, has been achieved. Both diastereomers, l - allo -enduracididine and l -enduracididine, were prepared via catalyst-controlled asymmetric nitroaldol reaction with the aldehyde precursor derived from l -aspartic acid. The cyclic guanidine of di-Cbz-protected l - allo -enduracididine was fully protected with an allyl group to suppress nucleophilic side reactions. Introduced allyl group was efficiently removed via π-allylpalladium chemistry without attaching the Cbz group on the cyclic guanidine moiety.