Z-Tyr[P(O)(NHR)2]-OBzl (R=n-Pr and i-Pr) were obtained by reactions of Z-Tyr-OBzl, lithiated with LDA, with N,N′-dipropyl- or diisopropyl-phosphorodiamidic chloride. Fmoc derivatives, Fmoc-Tyr[P(O)(NHR)2]-OH, were obtained from them as stable crystals. The PN bonds are stable toward 20% piperidine in DMF and were cleaved completely with 95% trifluoroacetic acid.