As a delivery system of cyclophosphamide(CP), 4-(poly-L-cysteine)cyclophosphamide(1) was synthesized. It has a drug loading of 28.3 mol% and average molecular weight($\mbox{\overline{Mn}}$) is 4274. The hydrolytic kinetics of 1 using $^{31}P$ NMR in 1 M lutidine buffer at pH 7.4, 37 ℃ showed first order reaction rate which gave half-life of 45 min, and showed that 4-hydroxycyclophosphamide(2) and aldophosphamide(3)/aldophosphamide hydrate(5)/thiohemiacetal(27) were appeared nearly at the same time. Also the kinetics exhibited that 1, 2, 3/5/27 were not equilibrated and the signal of 1 was being decreased and that of 3/5/27 was being increased till 70 min. After 2 increased until 40 min it stayed nearly constant and phosphoramide mustard(4) was not observed by 70 min. Based on the $\mbox{reports}^{38,39}$ these data were consistent with the facts that the signal of 3/5/27 contained mainly 27 and the rate of appearance of 27 was fast relative to the rate for 1. Thus this implicates that AP(3) to produce ultimate alkylating agent PM(4) exists in small amount. In vivo antitumor activity of 1 showed less T/C value than that of free CP and thus did not exhibited a promise for therapeutic effectiveness. However, these results could derive that 1 had abilities for delivery of 4-hydroxycyclophosphamide(2) and slow release of aldophosphamide(3) and that sulfhydryl in 1 might result in a decrease of cytocidal effect of parent drug.
