Selective phosphorylation of phenpanstatin (3a) with tetrabutylammonium dihydrogen phosphate and dicyclohexyl-carbodiimide in pyridine followed by cation exchange chromatographic procedures was found to provide an efficient mute to a new series (3b-3d) of promising 3,4-O-cyclic phosphate prodrugs designated phenpanstatin phosphates. Application of analogous reaction conditions to pancratistatin (1a) led to a mixture of monophosphate derivatives where sodium paancratistatin 4-O-phosphate (4a) was isolated and the structure confirmed by x-ray craxtallography. Modification of the reaction conditions allowed direct phosphorylation of pancratistatin followed by cation exchange chromatography to afford sodium pancratistatin 3,4-O-cyclic phosphate (5b) which was selected for preclinical development.