Synthesis Of New Potential Lipophilic Co-Drugs Of 2-Chloro-2 '-Deoxyadenosine (Cladribine, 2-Cda, Mavenclad (R), Leustatin (R)) And 6-Azauridine (Z(6)U) With Valproic Acid

2-Chloro-2 '-deoxyadenosine (cladribine, 1) was acylated with valproic acid (2) under various reaction conditions yielding 2-chloro-2 '-deoxy-3 ',5 '-O-divalproyladenosine (3) as well as the 3 '-O- and 5 '-O-monovalproylated derivatives, 2-chloro-2 '-deoxy-3 '-O-valproyladenosine (4) and 2-chloro-2 '-deoxy-5 '-O-valproyladenosine (5), as new co-drugs. In addition, 6-azauridine-2 ',3 '-O-(ethyl levulinate) (8) was valproylated at the 5 '-OH group (-> 9). All products were characterized by H-1- and C-13-NMR spectroscopy and ESI mass spectrometry. The structure of the by-product 6 (N-cyclohexyl-N-(cyclohexylcarbamoyl)-2-propylpentanamide), formed upon valproylation of cladribine in the presence of N,N-dimethylaminopyridine and dicyclohexylcarbodiimide, was analyzed by X-ray crystallography. Cladribine as well as its valproylated co-drugs were tested upon their cancerostatic/cancerotoxic activity in human astrocytoma/oligodendroglioma GOS-3 cells, in rat malignant neuro ectodermal BT4Ca cells, as well as in phorbol-12-myristate 13-acetate (PMA)-differentiated human THP-1 macrophages. The most important result of these experiments is the finding that only the 3 '-O-valproylated derivative 4 exhibits a significant antitumor activity while the 5 '-O- as well as the 3 ',5 '-O-divalproylated cladribine derivatives 3 and 5 proved to be inactive.