D-Phenylalanine, N-[O-(phenylmethyl)-N-[N-[O-(phenylmethyl)-N-[1-[N-[O-(phenylmethyl)- N-[N-[O-(phenylmethyl)-N-L-prolyl-L-seryl]glycyl]-L-seryl]-D-phenylalanyl]-L -prolyl]-L-seryl]glycyl]-L-seryl]