Enzymatic Synthesis of 2′-Deoxy-β-d-ribonucleosides of 8-Azapurines and 8-Aza-7-deazapurines

Abstract

The enzymatic synthesis of 8-azapurine and 8-aza-7-deazapurine 2′-deoxyribonucleosides has been studied. Two methods have been used: (i) transglycosylation employing 2′-deoxyguanosine, 2′-deoxycytidine, 2′-deoxyuridine, and 2′-deoxythymidine as 2-deoxy-d-ribofuranose donors and recombinant E. coli purine nucleoside phosphorylase (PNP) as biocatalyst, and (ii) one-pot synthesis from 2-deoxy-d-ribose and nucleobases employing recombinant E. coli ribokinase (RK), phosphopentomutase (PPM) and PNP as biocatalysts. Good substrate activity was observed for all bases studied except 2-amino-8-aza-6-chloro-7-deazapurine, which afforded the desired N ⁹-nucleoside in moderate yield due to very low solubility of the base and partial replacement of C6-chloro atom of the base and formed nucleoside with a hydroxy group. The participation of Ser90 O^γ of E. coli PNP in the binding of 8-aza-7-deazapurines in the catalytic center of PNP followed by the formation of a productive complex and glycosidic bond is suggested.

Key words

azapurine - nucleosides - enzyme catalysis - glycosylation - phosphorylases

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• 34 The following reaction conditions employed in these experiments: the ratio of donor to acceptor was 1.1:1.0 (mol), 10 mM K,Na-phosphate buffer (pH 7.0) containing 10% (vol) DMSO; 1000 units¹⁴ PNP per 1.0 mmol base, reaction temperature was 50 °C. The progress of the nucleoside formation was followed by HPLC column HYPERSIL 150 × 4.6 mm, 5 μm; eluent: H₂O; 1 mL/min; t _R = 4.1 (4), 6.0 (15), 2.0 (6), 5.9 (17) min