Enzymatic Synthesis of 2-Chloropurine Arabinonucleosides with Chiral Amino Acid Amides at the C6 Position and an Evaluation of Antiproliferative Activity In Vitro

A number of purine arabinosides containing chiral amino acid amides at the C6 position of the purine were synthesized using a transglycosylation reaction with recombinant E. coli nucleoside phosphorylases. Arsenolysis of 2-chloropurine ribosides with chiral amino acid amides at C6 was used for the enzymatic synthesis, and the reaction equilibrium shifted towards the synthesis of arabinonucleosides. The synthesized nucleosides were shown to be resistant to the action of E. coli adenosine deaminase. The antiproliferative activity of the synthesized nucleosides was studied on human acute myeloid leukemia cell line U937. Among all the compounds, the serine derivative exhibited an activity level (IC50 = 16 μM) close to that of Nelarabine (IC50 = 3 μM) and was evaluated as active.

Multi-Enzymatic Cascades in the Synthesis of Modified Nucleosides: Comparison of the Thermophilic and Mesophilic Pathways

A comparative study of the possibilities of using ribokinase → phosphopentomutase → nucleoside phosphorylase cascades in the synthesis of modified nucleosides was carried out. Recombinant phosphopentomutase from Thermus thermophilus HB27 was obtained for the first time: a strain producing a soluble form of the enzyme was created, and a method for its isolation and chromatographic purification was developed. It was shown that cascade syntheses of modified nucleosides can be carried out both by the mesophilic and thermophilic routes from D-pentoses: ribose, 2-deoxyribose, arabinose, xylose, and 2-deoxy-2-fluoroarabinose. The efficiency of 2-chloradenine nucleoside synthesis decreases in the following order: Rib (92), dRib (74), Ara (66), F-Ara (8), and Xyl (2%) in 30 min for mesophilic enzymes. For thermophilic enzymes: Rib (76), dRib (62), Ara (32), F-Ara (<1), and Xyl (2%) in 30 min. Upon incubation of the reaction mixtures for a day, the amounts of 2-chloroadenine riboside (thermophilic cascade), 2-deoxyribosides (both cascades), and arabinoside (mesophilic cascade) decreased roughly by half. The conversion of the base to 2-fluoroarabinosides and xylosides continued to increase in both cases and reached 20-40%. Four nucleosides were quantitatively produced by a cascade of enzymes from D-ribose and D-arabinose. The ribosides of 8-azaguanine (thermophilic cascade) and allopurinol (mesophilic cascade) were synthesized. For the first time, D-arabinosides of 2-chloro-6-methoxypurine and 2-fluoro-6-methoxypurine were synthesized using the mesophilic cascade. Despite the relatively small difference in temperatures when performing the cascade reactions (50 and 80 °C), the rate of product formation in the reactions with Escherichia coli enzymes was significantly higher. E. coli enzymes also provided a higher content of the target products in the reaction mixture. Therefore, they are more appropriate for use in the polyenzymatic synthesis of modified nucleosides.

Anion exchange resins in phosphate form as versatile carriers for the reactions catalyzed by nucleoside phosphorylases

In the present work, we suggested anion exchange resins in the phosphate form as a source of phosphate, one of the substrates of the phosphorolysis of uridine, thymidine, and 1-(β-ᴅ-arabinofuranosyl)uracil (Ara-U) catalyzed by recombinant E. coli uridine (UP) and thymidine (TP) phosphorylases. α-ᴅ-Pentofuranose-1-phosphates (PF-1Pis) obtained by phosphorolysis were used in the enzymatic synthesis of nucleosides. It was found that phosphorolysis of uridine, thymidine, and Ara-U in the presence of Dowex^® 1X8 (phosphate; Dowex-nPi) proceeded smoothly in the presence of magnesium cations in water at 20-50 °C for 54-96 h giving rise to quantitative formation of the corresponding pyrimidine bases and PF-1Pis. The resulting PF-1Pis can be used in three routes: (1) preparation of barium salts of PF-1Pis, (2) synthesis of nucleosides by reacting the crude PF-1Pi with an heterocyclic base, and (3) synthesis of nucleosides by reacting the ionically bound PF-1Pi to the resin with an heterocyclic base. These three approaches were tested in the synthesis of nelarabine, kinetin riboside, and cladribine with good to excellent yields (52-93%).