CHARACTERIZATION OF PLATINUM(II)-PHOSPHATO COMPLEXES OF URIDINE NUCLEOTIDES

Reactions of uridine 5'-di- and -triphosphates with cis-diamminedichlo roplatinum(II) at or near neutral pH yielded substantial phosphato che lates. Each nucleotide afforded a pair of diastereomers due to the cre ation of an asymmetric center at the alpha- and beta-phosphorus atoms of the UDP and UTP upon complexation to platinum(II). In addition to t he phosphato complexes, nitrogen(N(3)) bound complexes are also formed . Further, secondary reaction of these pyrimidine base bound complexes resulted in platinum blue (for UDP) and purple (for UTP) complexes as minor products. Diastereomers are separated by reversed phase HPLC me thod and characterized by one- and two-dimensional phosphorus-31 NMR a nd CD spectroscopic methods. The phosphorus atoms of the coordinated p hosphate groups exhibit 8-12 ppm coordination chemical shifts. For the UDP complexes, distinct P-31 resonances for each diastereomer were ob served. The coordinated gamma-phosphate of UTP diastereomers exhibited a broad multiplet while the beta-phosphate group showed distinct doub lets of doublet. The CD spectra of the UDP diastereomers displayed opp osite Cotton effects at 300 nm while both complexes exhibited a positi ve Cotton effect at 260 nm. Once separated, these diastereomers slowly (t1/2 = 25 +/- 5) redistribute to a mixture of two with almost equal abundance. Kinetic studies based on HPLC and P-31 NMR measurements poi nt to a mechanism in which the isomerization proceeds through a rate l imiting ring-opening. When the chelate ring is opened, deligation and phosphate hydrolysis can also occur, resulting in free UDP, UMP, and o rthophosphate bound to platinum.