(R)-tert-butyl 3-(4-{4-[bis(2-chloroethyl)amino]phenyl}butyryloxy)-4-[N,N-bis(2-tert-butyldiphenylsilyloxyethyl)amino]butyrate
(R)-tert-butyl 3-octanoyloxy-4-[N,N-bis(2-tert-butyldiphenylsilyloxyethyl)amino]butyrate
(R)-tert-butyl 3-phenylacetyloxy-4-[N,N-bis(2-tert-butyldiphenylsilyloxyethyl)amino]butyrate