Preparation of an Octadeoxyribonucleoside Heptaphosphorothioate by the Phosphotriester Approach in Solution

Abstract

The synthesis of the octadeoxyribonucleoside heptaphosphorothioate, d[Tp(s)Tp(s)Gp(s)Gp(s)Gp(s)Gp(s)Tp(s)Vby the phosphouiester approach in solution is described. The phosphorothioate internucleotide linkages are protected by the S-(2-cyanoethyl) group and 1 -(mesitylene-2-sulfonyl)-3-nitro-1,2,4-lhl-triazole (MSNT) is used as the coupling agent. A block synthesis strategy (2 + 2 + 4 and 4 + 4 + 8) is followed. INTRODUCTIONIn the past few years, there has been considerable interest in the large scale synthesis of phosphorothioate analogues1.2 of oligodeoxyribonucleides. A number of specific sequences have shown promise as chemotherapeutic agents, and several are at present undergoing clinical uiald. It appears from the literature that the consequent need for relatively large (certainly of the order of hundreds of grams and @ssibly considerably more) quantities of specific oligodeoxyribonucleotide phosphorothioates has almost

Aryl H-phosphonates. Part 13.1 A new, general entry to aryl nucleoside phosphate and aryl nucleoside phosphorothioate diesters

“…One should note, however, that aryl phosphorothioates as nucleotidic components seemed particularly appealing, as using electron-deficient aryl derivatives in combination with highly chemoselective condensing agent 20,21 may appear to be an attractive alternative to the S-protection required in some methods for oligonucleoside phosphorothioate synthesis. [22][23][24] These facts, and the growing interest in recent years in the phosphotriester method as means of synthesising oligonucleotides and their analogues on a large scale, prompted us to search for a convenient method permitting preparation of aryl nucleoside phosphates and phosphorothioates bearing aryls derived from phenols of a wide range of acidity (pK a 1.0-10.0). As part of our studies in developing new, efficient methods for the preparation of biologically important phosphate esters and their analogues using H-phosphonate methodology, we report here on a new, general entry to aryl nucleoside phosphates and their phosphorothioate analogues.…”

Solution phase synthesis of ISIS 2922 (Vitravene) by the modified H-phosphonate approach

“…These building blocks were obtained from 4-N-benzoyl-5Ј-O-(4,4Ј-dimethoxytrityl)-2Ј-deoxycytidine 9; B = 10, 5Ј-O-(4,4Ј-dimethoxytrityl)-2-Nisobutyryl-2Ј-deoxyguanosine 9; B = 11 and 5Ј-O-(4,4Јdimethoxytrityl)thymidine 9; B = 13, all of which were commercially available. In order to minimize side-reactions and to increase the solubility of the protected oligonucleotide intermediates in organic solvents, it was decided to protect guanine residues also on O-6 with the 2,5-dichlorophenyl group 12 and thymine residues on O-4 with the phenyl group. 13 The 2Јdeoxyguanosine derivative 9; B = 11 was converted in high yield into its 6-O-(2,5-dichlorophenyl) derivative 9; B = 12 by a previously reported procedure 12 and the thymidine derivative 9; B = 13 was converted (Scheme 2a and Experimental) into its 4-O-phenyl derivative 9; B = 14 in 82% isolated yield.…”

“…In order to minimize side-reactions and to increase the solubility of the protected oligonucleotide intermediates in organic solvents, it was decided to protect guanine residues also on O-6 with the 2,5-dichlorophenyl group 12 and thymine residues on O-4 with the phenyl group. 13 The 2Јdeoxyguanosine derivative 9; B = 11 was converted in high yield into its 6-O-(2,5-dichlorophenyl) derivative 9; B = 12 by a previously reported procedure 12 and the thymidine derivative 9; B = 13 was converted (Scheme 2a and Experimental) into its 4-O-phenyl derivative 9; B = 14 in 82% isolated yield. All three 5Ј-O-DMTr derivatives 9; B = 10, 12 and 14 were converted (Scheme 2b, step iii) into the triethylammonium salts of their 3ЈH-phosphonates 1, B = 10, 12 and 14, respectively, in high yields by a previously reported procedure 14 and into the corresponding 3Ј-O-levulinyl derivatives 15, B = 10, 12 and 14 in good yields.…”

“…Levulinic anhydride 12 (2.14 g, 10.0 mmol) was added to a stirred solution of 5Ј-O-(4,4Ј-dimethoxytrityl)-4-O-phenylthymidine 9; B = 14 (3.16 g, 5.09 mmol), triethylamine (1.75 cm 3 , 12.6 mmol) and 4-(dimethylamino)pyridine (0.050 g, 0.41 mmol) in dry dichloromethane (25 cm 3 ) at room temperature. After 1 h, the products were poured into saturated aqueous sodium hydrogen carbonate (30 cm 3 ).…”

2-(Phenylthio)ethyl as a Novel Two-Stage Base Protecting Group for Thymidine Analogues

“…To the best of our knowledge, there is only one example reported in the literature of alternative protection for thymine residues in oligonucleotide synthesis, involving N-acylation of the heterocycle with p-anisoyl chloride. 5 More stringent is the choice of the protecting groups for thymine and uracil nucleosides, in case a selective manipulation of the ribose functions is desired to obtain sugar-modified analogues. Benzyl, p-methoxybenzyl and benzyloxymethyl groups have been preferentially adopted to this purpose.…”