A series of cycloSal-phosphate prodrugs of a recently described new class of nucleoside cytostatics (6-hetaryl-7-deazapurine ribonucleosides) was prepared. The corresponding 2',3'-isopropylidene 6-chloro-7-deazapurine nucleosides were converted into 5-O'-cycloSal-phosphates. These underwent a series of Stille or Suzuki cross-couplings with diverse (het)arylstannanes or -boronic acids to yield the protected 6-(het)aryl-7-deazapurine pronucleotides that were subsequently deprotected to give 12 derivatives of free pronucleotides. The in vitro cytostatic effect of the pronucleotides was compared with parent nucleoside analogues. In most cases, the activity of the pronucleotide was similar to or somewhat lower than that of the corresponding parent nucleosides, with the exception of 7-fluoro pronucleotides 13 a, 13 b, and 13 d, which had exhibited GIC(50) values that were improved by one order of magnitude (to the low nanomolar range). The presence of a cycloSal-phosphate group also influenced selectivity toward various cell lines. Several pronucleotides were found which strongly inhibit human adenosine kinase but only weakly inhibit the MTB adenosine kinase.

Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic Gilead Sciences and IOCB Research Center Prague Czech Republic

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Pyrrolo[2,3-d]pyrimidine (7-deazapurine) as a privileged scaffold in design of antitumor and antiviral nucleosides