A.V. Smirnov - Dr.Sc. (Chem.), Yaroslavl State Pedagogical University named after K.D. Ushinsky. E-mail: sav_work@mail.ru
S.V. Baykov - Ph.D. (Chem.), Yaroslavl State Pedagogical University named after K.D. Ushinsky. E-mail: sv.baykov@pharmoslalvl.ru
V.B. Lyskov - Ph.D. (Chem.), Yaroslavl State Pedagogical University named after K.D. Ushinsky. E-mail: vb.lyskov@pharmoslalvl.ru
A.A. Shetnev - Ph.D. (Chem.), Yaroslavl State Pedagogical University named after K.D. Ushinsky. E-mail: aa.shetnev@pharmoslalvl.ru
I.D. Konstantinova - Ph.D. (Chem.), Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS (Moscow). E-mail: kid1968@yandex.ru
M.V. Dorogov - Dr.Sc. (Chem.), Professor, Yaroslavl State Pedagogical University named after K.D. Ushinsky. E-mail: dorogov@pharmoslalvl.ru

Cladribine is a modern anticancer drug with a broad spectrum of action which is used in the therapy of a wide range of different diseases. This range is growing fast due to a large amount of new clinical researches being undertaken in our days. Due to the constant growth of attention to Cladribine the search of new effective methods of its synthesis is of current interest. First proposed approaches to the synthesis of the drug were based on alkylation of N9-atom in purine cycle. In the early scientific publications alkylation of 2,6-dichloropurine 1,3,5-tri-O-acetyl-2-deoxy-D-ribofuranose and subsequent ammonolysis of the resulting mixture of anomers with following separation by column chromatography and fractional recrystallization is described. This stage is aimed at synthesis of both anomers. Later research found that the highest biological activity is exhibited by β-D-furanozilpuriny, that is why further development of synthetic methods relates to this anomer. A way to increase the stereoselectivity is to use the sodium salt of 2,6-dichloropurine with various ribofuranosyles as alkylators. The reaction proceeds stereospecifically, however low regioselectivity is shown. Later substrates with bulky substituents at the N7 atom of the purine cycle were suggested to increase regioselectivity. The best results were achieved using the methods based on preliminary silylation of the purine fragment. At the same time other methods, based on modification of the available natural nucleoside guanosine, adenosine and some others fragments were developed. A crucial role in this case play diazotization reaction and nucleophilic aromatic substitution. A special group of methods for the synthesis of cladribine is based on enzymatically catalyzed transglycosylation reaction, which is tconcerned with the transfer of deoxsyriboze-fragment from one (donor) to another (acceptor) nitrogenous base . In our days the highest stereo- and regeoselektivity is shown for enzymes-based methods in which case they are concidered as a highly promissing way for cladribines synthesis.

1. Bryson H.M. Sorkin E.M. Cladribine // Drugs. 1993. V. 46. P. 872-894.
2. Robak T., WierzbowskaA., RobakE. Recent clinical trials of cladribine in hematological malignancies and autoimmune disorders // Reviews on recent clinical trials. 2006. V. 1. P. 15-34.
3. Piro L.D., Carrera C.L., Carson D.A., Beutler E. Lasting remissions in hairy-cell leukemia induced by a single infusion of 2-chlorodeoxyadenosine // N. Engl. J. Med. 1990. V. 322. P. 1117-1121.
4. Jehn U., Bartl R., Dietzfelbinger H. et al. Long-term outcome of hairy cell leukemia treated with 2-chlorodeoxyadenosine // Ann. Hematol. 1999. V. 78. P. 139-144.
5. Zinzani P.L., Tani M., Marchi E. et al. Long-term follow-up of front-line treatment of hairy cell leukemia with 2-chloro­deoxyadenosine // Haematologica. 2004. V. 89. P. 309-313.
6. Chadha P., Rademaker A.W., Mendiratta P. et al. Treatment of hairy cell leukemia with 2-chlorodeoxyadenosine (2-CdA): long-term follow-up of the Northwestern University experience // Blood. 2005. V. 106. P. 241-246.
7. Sanata V.M., Mirro J., Kearns C. et al. 2-Chlo­rodeoxyadenosine produces a high rate of complete hematologic remission in replaced acute myeloid leukemia // J. Clin. Oncol. 1992. V. 10. P. 364-370.
8. Kong L.R., Samuelson E., Rosen S.T. et al. 2-Chloro­deoxyadenosine in cutaneous T-cell lymphoproliferative disorders // Leuk. Lymphoma. 1997. V. 26. P. 89-97.
9. Piro L.D., Carrera C.J., Beutler E., Carson D.A. 2-Chlorodeoxyadenosine: an effective new agent for the treatment of chronic lymphocytic leukemia // Blood. 1988. V. 72. P. 1069-1073.
10. Robak T., Belonski J., Kasznicki J. et al. The effect of subsequent therapies in patients with chronic lymphocytic leukemia previously treated with prednisone and either 2-CdA or chlorambucil // Hematilogy J. 2005. V. 90. P. 998-1000.
11. Robak T., Gora-Tybor J., Krykowski E. et al. Activity of 2-chlorodeoxyadenosine (cladribine) in 2-hour intravenous infusion in 94 previously treated patients with low grade non-hodgkin-s lymphoma // Leuk. Lymphoma. 1997. V. 26. P. 99-105.
12. Weber D.M., Dimopoulos M.A., Delasalle K. et al. 2-Chlorodeoxyadenosine alone and in combination for previously untreated Waldenstrom-s macroglobulinemia // Semin. Oncol. 2003. V. 30. P. 243-247.
13. Saarinen U.M., Wikstrom S., Koskimies O., Sariola H. Percutaneous needle biopsy preceding preoperative chemotherapy in the management of massive rental tumors in children // J. Clin. Oncology. 1991. V. 9. 406-415.
14. Robak T. Cladribine in the treatment of chronic lymphocytic leukemia // Leuk. Lymphoma. 2001. V. 40. P. 551-564.
15. Pettit A.R. Mechanism of action of purine analogues in chronic lymphocytic leukemia // Br. J. Haematol. 2003. V. 121. P. 692-702.
16. Beutler E., Sipe J.C., Romine J.S. et al. The treatment of chronic progressive multiple sclerosis with Cladribine // J. Proc. Natl. Acad. Sci. USA. 1996. V. 93. P. 1716-1720.
17. Giovannoni G. Comi G., Cook S. et al. A placebo-controlled trial of oral cladribine for relapsing multiple sclerosis // N. Engl. J. Med. 2010. V. 362. P. 416-426.
18. Sneader W. Drug discovery: A History. John Wiley and sons LTD. 2005. 468 p.
19. Robins M.J., Robins R.K. Purine Nucleosides. XI. The synthesis of 2'-deoxy-9-α- and -β-D-ribofuranosylpurines and the correlation of their anomeric structure with proton magnetic resonance spectra // J. Am. Chem Soc. 1965. V. 87. Р. 4934-4940.
20. Ikehara M., Tada H. A new type of «cyclonucleoside» derived from 2-chloro-8-mercapto-9-β-D-xylofuranosyladenine // J. Am. Chem. Soc. 1963. V. 85. P. 2344-2345.
21. Ikehara M., Tada H. Studies of nucleosides and nucleotides. XXIV. Purine cyclonucleosides. I. 8,2?-cyclonucleoside derived from 2-chloro-8-mercapto-9-β-D-xylofuranisyladenine // J. Am. Chem. Soc. 1965. V. 87. P. 606-609.
22. Christensen L.F., Broom A.D., Robins M.J., Bloch A. Synthesis and biological activity of selected 2,6-disubstituted(2-deoxy-α-and-β-D-erythropentofuranosyl)purines // J. Med. Chem. 1972. V. 15. P. 735-738.
23. Robins M.J., Khwaja T.A., Robins R.K. Purine Nucleosides. XXIX. The synthesis of 2?-deoxy-L-adenosine and 2?-deoxy-L-guanosine and their α-anomers // J. Org. Chem. 1970. V. 35. P. 636-639.
24. Kazimierczuk Z., Cottam H., Revancar G., Robins R. Synthesis of 2'-deoxytubercidin, 2'-deoxyadenosine, and related 2'-deoxynucleosides via a novel direct stereospecific sodium salt glycosylation procedure // J. Am. Chem. Soc. 1984. V. 106. P. 6379-6382.
25. Patent 0173059 A2 EP. Method for the production of 2?-deoxyadenosine compounds / R.K. Robins, G.R. Revankar.
26. Zhong M., Nowak I., Robins M.J. Regiospecific and highly stereoselective coupling of 6-(substituted-imidazol-1-yl)purines with 2-deoxy-3,5-O-(p-toluyl)-α-D-erythro-pen­tofuranosyl chloride/sodium salt glycosylation in binary solvent mixtures: improved synthesis of cladribine // J. Org. Chem. 2006. V. 71. P. 7773-7779.
27. Patent 2002/052491 A1 US. Method for the production of 2-chloro-2'-deoxyadenosine (cladribine) and its 3,5-di-O-p-toluoyl derivative / G. Szepsel, A. Daniel.
28. Secrist M., Saneyoshi E.S. Synthetic Nucleosides and Nucleotides. XIII. Stannic chloride catalyzed ribosylation of several 6-substituted purines // Chem. Pharm. Bull. 1979. V. 27. P. 2518-2521.
29. Andrzejewska M. Kaminski J., Kazimierczuk Z. Microwave induced of Ribonucleosides on solid support // Nucleosides, Nucleotides and Nucleic Acids. 2002. V. 21. P. 73-78.
30. Marchand A., Lioux T., Mathe C. et al. Stereospecific synthesis of unnatural β-L-enantiomers of 2-chloro-adenine pentofuranonucleoside derivatives // J. Chem. Soc., Perkin Trans. 1. 1999. P. 2249-2254.
31. Hildebrand C., Wright G.E. Sodium salt glycosilation in the synthesis of purine 2?-deoxyribonucleosides: studies of isomer distribution // J. Org. Chem. 1992. V. 57. P. 1808-1813.
32. Yang F., Zhu Yu., Yu B. A dramatic concentration effect on the stereoselectivity of N-glycosylation for the synthesis of 2?-deoxy-b-ribonucleosides // Chem. Commun. 2012. V. 48. P. 7097-7099.
33. Patent US 2004/39190 A1. Process for the preparation of 9-beta-anomeric nucleoside analogs / P.K. Gupta, S.A. Munk.
34. Patent 2006/138396 A2 WO. Methods for selective N-9 glycosylation of purine / M.J. Robins, M. Zhong.
35. Dudycz L.W., Wright G.E. A simple one-pot method for 6-oxopurine ribonucleoside synthesis: control and mechanism of isomer distribution // Nucleosides & Nucleotides. 1984. V. 3. P. 33-44.
36. Wright G.E., Dudycz L.W. Synthesis and characterization of N2-(p-n-butylphenyl)-2?-deoxyguanosine and its 5?-triphos­phate and their inhibition of HeLa DNA polymerase. alpha // J. Med. Chem. 1984. V. 27. P. 175-181.
37. Garner Ph., Ramakanth S. A regiocontrolled synthesis of N7- and N9-guanine nucleosides // J. Org. Chem. 1988. V. 53. P. 1294-1298.
38. Sheppard T.L., Rosenbaltt A.T., Breslow R. Preparation of 2?-O-(.beta.-cyanoethyl phosphoramidites) of 3?-deoxycytidine and 3?-deoxyguanosine and their use for solid-phase sytnesis of oligodeoxynucleotides contain 2?,5?-phosphodiesters linkages // J. Org. Chem. 1994. V. 59. P. 7243-7248.
39. Hunziker J., Priestley E.S., Brunar H., Dervan P.B. Design of an N7-glycosylated purine nucleoside for recognition of GC Bace Pairs bytriple helix formation // J. Am. Chem Soc. 1995. V. 117. P. 2661-2662.
40. Robins M.J., Zou R., Guo Zh., Wnuk S.F. Nucleic acid related compound. 93. A solution for the historic problem of regioselective sugar-base coupling to produse 9-glycosylguaninesor 7-glycosylguanines // J. Org. Chem. 1996. V. 61. P. 9207-9212.
41. Worthington V.L., Fraser W., Schwalbe C.H. The N-7 regioisomer of 2-chloro-2?-deoxyadenosine: synthesis, crystal structure, conformation, and stability // Carbohydrate Research. 1995. V. 275. P. 275-284.
42. Patent 2011020298 A1 WO. Process for the preparation of cladribine / J.P. Henschke, X. Zhang, G. Chu, L. Mai, Yu. Chen.
43. Lioux T., Gosselin G., Mathéi C. Azido/tetrazole tautomerism in 2-Azidoadenine β-D-pentafuranonu-cleoside derivatives // Eur. J. Org Chem. 2003. V. 20. P. 3997-4002.
44. Xu Sh. Yao P., Chen G., Wang H. A new synthesis of 2-chloro2?-deoxyadenosine (Cladribine), Cda) // Nucleosides, Nucleotides and Nucleic acids. 2011. V. 30. P. 353-359.
45. Sakakibara N., Kakoh A., Maruyama T. First synthesis of [6-15N]Cladribine using ribonucleoside as a starting material // Heteocycles. 2012. V. 85. P. 171-182.
46. Patent 5208327 A US. Intermediates useful in a synthesis of 2-chloro-2?-deoxyadenosine / R.H.K. Chen, B. Mead.
47. Janeba, Z. Francom P., Robins M.J. Efficient syntheses of 2-chloro-2'-deoxyadenosine (Cladribine) from 2?-deoxygua­nosine // J. Org. Chem. 2003. V. 68. P. 989-992.
48. Patent 6252061 B1 US. Process for the production of 2-halo-6-aminopurine derivatives / U. Sampath, L. Bartlett.
49. Peng Ya. A practical synthesis of 2-chloro-2?-deoxyadenosine (Cladribine) from 2?-deoxyadenosine // J. Chem. Res. 2013. P. 213-215.
50. Cardinaud R. Nucleoside deoxyribosyltransferase from Lactobacillus helveticus // Methods in Enzymol. 1978. V. 60. P. 446-455.
51. Huang M.-Ch., Hatfield K., Roetker A.W. et. al. Analogs of 2?-deoxyadenosine: facile enzymatic preparation and growth inhibitory effects on human cell lines // Biochemical Pharmacology. 1981. V. 30. P. 2663-2671.
52. Blank W.A. Elder K.J., Gati W.P. et al. Synthesis of 2-chloro-2?-deoxyadenosine by washed cells of E. coli // Biotech. lett. 1992. V. 14. P. 669-672.
53. Votruba I., Holy А., Dvorakova H. et al. Synthesis of 2-deoxy-β-D-ribonucleosides and 2,3-dideoxy-β-D-pento­furanosides on immobilized bacterial cells // Coll. Czech. Chem. Commun. 1994. V. 59. P. 2303-2330.
54. Mikhailopulo I.A., Zinchenko A. I., Kazimierczuk Z. et al. Synthesis of 2-chloro-2?-deoxyadenosine by microbiological transglycosylation // Nucleosides and Nucleotides. 1993. V. 12. P. 417-422.
55. Barai V.N., Zinchenko A.I., Eroshebskaya L.A. et al. A universal biocatalyst for the preparation of base- and sugar-modified nucleosides via an enzymatic transglycosylation // Helvetica chimica Act. 2002. V. 85. P. 1901-1908.
56. Taran S.A., Verevkina K.N., Feofanov S.A., Miroshnikov A.I. Enzymatic transglycosylation of natural and modified nucleosides by immobilized thermostable nucleoside phosphorylases from Geobacillus stearothermophilus //Russian Journal of Bioorganic Chemistry. 2009. V. 35. P. 739-745.
57. Komatsu H., Araki T. Еfficient chemo-enzymatic syntheses of pharmaceutically useful unnatural 2′-deoxynucleosides // Nucleosides, Nucleotides and Nucleic Acids. 2005. V. 24. P. 1127-1130.