204978-87-0

Two approaches to the chemoenzymatic synthesis of 2-fluorocordycepin and 2-chlorocordycepin were studied: (i) the use of 3′-deoxyadenosine (cordycepin) and 3′-deoxyinosine (3′dIno) as donors of 3-deoxy- d -ribofuranose in the transglycosylation of 2-fluoro- (2F Ade) and 2-chloroadenine (2Cl Ade) catalyzed by the recombinant E. coli purine nucleoside phosphorylase (PNP), and (ii) the use of 2-fluoroadenosine and 3′-deoxyinosine as substrates of the cross-glycosylation and PNP as a biocatalyst. An efficient method for 3′-deoxyinosine synthesis starting from inosine was developed. However, the very poor solubility of 2Cl Ade and 2F Ade is the limiting factor of the first approach. The second approach enables this problem to be overcome and it appears to be advantageous over the former approach from the viewpoint of practical synthesis of the title nucleosides. The 3-deoxy-α- d -ribofuranose-1-phosphate intermediary formed in the 3′dIno phosphorolysis by PNP was found to be the weak and marginal substrate of E. coli thymidine (TP) and uridine (UP) phosphorylases, respectively. Finally, one-pot cascade transformation of 3-deoxy- d -ribose in cordycepin in the presence of adenine and E. coli ribokinase, phosphopentomutase, and PNP was tested and cordycepin formation in ca. 3.4% yield was proved.

Two industrial synthetic approaches to Lodenosine (1, FddA, 9-(2,3-dideoxy-2-fluoro-β-D-threo-pentofuranosyl) adenine) via a purine riboside or a purine 3′-deoxyriboside are described. Several novel applications of deoxygenation and fluorination methods are compared considering reaction yields, economy, safety and environmental concerns.

There can be provided an excellent industrial process for producing compounds having sugar-moiety hydroxyl groups or halogen atoms reduced in nucleic acids or in derivatives thereof by allowing O-thiocarbonyl derivatives of sugar-moiety hydroxyl groups or allowing halogenated derivatives in the sugar-moiety, in the nucleic acids or in derivatives thereof to react with any one of hypophosphorous acids (including salts thereof) and phosphites (esters) which are inexpensive, non-toxic and safely usable as radical reducing agents in industrial scale, in the presence of a radical reaction initiator. The process of the present invention is an industrially useful and highly safe process for reducing sugar-moiety hydroxyl groups and halogen atoms in nucleic acids or derivatives thereof (including nucleic acid-related compounds) at low costs.

A synthesis of 9-(2,3-dideoxy-2-fluoro-β-D-threo-pentofuranosyl)adenine (1, FddA) via a 6-chloro 9-(3-deoxy-β-D-erythro-pentofuranosyl)-9H-purine (9), which was readily obtained from inosine (5), is described. Fluorination at the C2′-β position of the purine 3′-deoxynucleoside with diethylaminosulfur trifluoride was improved by the introduction of a 6-chloro group and proceeded in moderate yield. Purine 3′-deoxynucleoside derivatives were also subjected to nucleophilic reactions with triethylamine trihydrofluoride and gave the desired fluorinated nucleoside in good yield. The safety and yield of the fluorination process were greatly improved by the use of triethylamine trihydrofluoride. The influence of the sugar ring conformation and 6-chloro group on the rate of the nucleophilic reaction against elimination are also discussed.

Based on the recently developed lithiation-mediated stannyl migration of 6-chloropurine derivatives, 2-iodocordycepin was prepared from cordycepin. The reaction of this compound with terminal alkynes was carried out to synthesize a series of 2-alkynyl der