Chemo-Enzymatic Synthesis of 3-Deoxy-β-D-ribofuranosyl Purines

9-(3-Deoxy-β-D-erythro-pentofuranosyl)-2,6-diaminopurine (6) was synthesized by an enzymatic transglycosylation of 2,6-diaminopurine (2) with 3′-deoxycytidine (1) as a donor of 3-deoxy-D-erythro-pentofuranose moiety. This transformation comprises i) deamination of 1 to 3′-deoxyuridine (3) under the action of whole cell (E. coli BM-11) cytidine deaminase (CDase), ii) the phosphorolytic cleavage of 3 by uridine phosphorylase (UPase) giving rise to the formation of uracil (4) and 3-deoxy-α-D-erythro-pentofuranose-1-O-phosphate (5), and iii) coupling of the latter with 2 catalyzed by whole cell (E. coli BMT-4D/1A) purine nucleoside phosphorylase (PNPase). Deamination of 6 by adenosine deaminase (ADase) gave 3′-deoxyguanosine (7). Treatment of 6 with NaNO2 afforded 9-(3-deoxy-β-D-erythro-pentofuranosyl)-2-amino-6-oxopurine (3′-deoxyisoguanosine; 8). Schiemann reaction of 6 (HF/HBF4+NaNO2) gave 9-(3-deoxy-β-D-erythro-pentofuranosyl)-2-fluoroadenine (9).