with potassium carbonate in methanol. Compound 10cr7] was obtained as a mixture of four stereoisomers, since the phosphorus atom is also a stereogenic center and the phosphorylation with 9 proceeded, as expected, in a nonstereoselective fashion. All the compounds reported here are very acid labile, so that chromatography is only possible in the presence of triethylamine.
The stereochemistry of 1Oc at the anomeric center is revealed by the doublet for 1-H at 6 = 4.53 (J = 8 Hz) in the 'H NMR spectrum.[*] The configuration at C-2' is assigned on the basis of the I3C NMR signals for C-1' and C-3'. We assume that, by analogy to the NMR datac4] for the acetal glycosides of aldehydes, the signals in the spectrum of the (2'R) epimer lie at lower field for C-I' and higher field for C-3', compared to the corresponding signals of the (2's)
isomer.
The kinetics of the acid-catalyzed hydrolysis[91 of 1Oc was determined using NMR spectroscopy. The first-order rate constant for deuterolysis at pD = 6.10 in phosphate buffer at 35 " c (0.10
Assuming a kDm/kH, value of 1 .5,['01 1Oc has a half-time for hydrolysis of 15 h at pH = 6.2 and 35 "C. This value roughly corresponds to the desired value. Cleavage of 1Oc yields besides glucose and methanol, the diamidophosphate 11 (ketophosphamide)," 'I which, via either elimination or hydrolysis, is converted into the cytotoxic phosphoramide mustard 12 in the cell. This compound is also the active metabolite of the clinically used cytostatic drug cyclophosphamide. [' 21 The dependence of the cytostatic activity of 1Oc on pH was determined in vitro by treating mammary carcinoma cells (MI R) of Marshall rats for 24 h. At physiological extracellular pH (pH, = 7.4) and a concentration of 10 pg mL-', nearly no toxicity was observed; at pH, = 6.2, however, under otherwise indentical conditions, the survival rate of the cancer cells decreased by a factor of 5 x lo4. We are currently using transplanted tumors to investigate whether this surprisingly high selectivity is also exhibited in vivo