5'-Chalcogen-Substituted Nucleoside Pyrophosphate and Phosphate Monoester Analogues: Preparation and Hydrolysis Studies

Novel sulfur and selenium substituted 5',5'-linked dinucleoside pyrophate analogues were prepared in a vibration ball mill from the corresponding persilylated monophosphate. The chemical hydrolysis of pyrophosphorochalcogenolate-linked dimers was studied over a wide pH-range. The effect of the chalcogeno-substitution on the reactivity of dinucleoside pyrophosphates was surprisingly modest, and the chemical stability is promising considering the potential therapeutic or diagnostic applications. The chemical stability of the precursor phosphorochalcogenolate monoesters was also investigated. Hydrolytic desilylation of these materials was effected in aqueous buffer at pH 3, 7 or 11 and resulted in phosphorus-chalcogen bond scission which was monitored using ³¹P NMR. The rate of dephosphorylation was dependent upon both the nature of the chalcogen and the pH. The integrity of the P-S bond in the corresponding phosphorothiolate was maintained at high pH but rapidly degraded at pH 3. In contrast, P-Se bond cleavage of the phosphoroselenolate monoester was rapid and the rate increased with alkalinity. The results obtained in kinetic experiments provide insight on the reactivity of the novel pyrophosphates studied as well as of other types of thiosubstituted biological phosphates. At the same time, these results also provide evidence for possible formation of unexpectedly reactive intermediates as the chalcogen-substituted analogues are metabolised.

Vibration Ball Milling for the Synthesis of 5'-Thioadenosine 5'-Pyrophosphate (P'→5') Adenosine (dASppA)

Using vibration ball milling, 5'-chloro-5'-deoxyadenosine (CldA) reacts cleanly with 4-methoxybenzyl mercaptan (MobSH), under basic conditions, to the corresponding thioether (MobSdA), which is isolated following precipitation and trituration. Under acidic conditions, in a one-pot, two-step process, MobSdA is transformed into 5'-deoxy-5'-(5-nitropyridyl-2-disulfanyl)-adenosine (NPySSdA). Michaelis-Arbuzov (M-A) reaction of NPySSdA with tris(trimethylsilyl) phosphite proceeds to completion within 30 min as determined by ³¹ P NMR, and the persilylated M-A product thus formed can be stored in solution under anhydrous conditions at room temperature for several days (in contrast, the anionic phosphorothiolate monoester is labile to hydrolysis). Following evaporation, mechanochemical mixing of the crude M-A product with the nucleotide donor adenosine 5'-monophosphomorpholidate under acidic activation in the presence of additional water gives rapid hydrolytic desilylation and phosphate coupling, so that essentially complete reaction is observed after 90 min and dASppA isolated following C-18 reversed phase HPLC and desalting (>99% pure as determined by monitoring at 260 nm). © 2017 by John Wiley & Sons, Inc.