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Synlett 2006(9): 1331-1334  
DOI: 10.1055/s-2006-941577
LETTER
© Georg Thieme Verlag Stuttgart · New York

One-Pot Synthesis of Dinucleoside (3′,5′)-Methylphosphonothioates and their Seleno Congeners via the Phosphonotriazolidite Approach

Lucyna A. Wozniak*, Malgorzata Bukowiecka-Matusiak, Marcin Gora, Wojciech J. Stec
Department of Bioorganic Chemistry, Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, 112 Sienkiewicza St, 90-363 Lodz, Poland
Fax: +48(42)6815383.; e-Mail: lawozn@bio.cbmm.lodz.pl;
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Publication History

Received 12 December 2005
Publication Date:
22 May 2006 (online)

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Abstract

An efficient method for large laboratory scale synthesis of dinucleoside (3′,5′)-methylphosphonothioates and their ­methylphosphonoselenoate congeners is presented. Bis-(1,2,4-tri­azoloyl)methylphosphonite generated in situ from methyldichlorophosphine is used as a phosphitylating agent and the preparations are performed as one-pot-reactions without isolation of the reactive PIII intermediates.

Key words

oligonucleotides - dinucleoside - phosphonoselenoate

1

Current address: L. A. Wozniak, Medical University of Lodz, Chair of Endocrinology and Metabolic Diseases, Department of Structural Biology, 90-752 Lodz, 7/9 Zeligowskiego, Poland.

17

The reactions of 2′-OMe ribonucleosides, not reported here in detail, required prolonged reaction times (first step: 1.5, second step usually about 2-2.5 h).

18

General Procedure for Synthesis of Dinucleoside (3′,5′)-Methylphosphonothioates 2 or Dinucleoside (3′,5′)-Methylphosphonoselenoates 3 (1-mmol Scale). A solution of 1,2,4-triazole (0.346 g, 5 equiv) and Et3N (0.56 mL, 4 equiv) in dry THF (5 mL) was cooled in an ice bath and MePCl2 (0.094 mL, 1.1 equiv) was added with vigorous stirring. After 30 min a solution of 5′-O-DMT-(N-protected)-nucleoside 8 (1 equiv) in THF (5 mL) was added dropwise at 0 °C. Stirring was continued for 30 min, followed by addition of the 3′-O-protected nucleoside 11 (1.2 equiv) in THF (5 mL). The reaction mixture was warmed up to r.t., stirred for additional 1.5 h, and sulfur or selenium (2-3 fold excess) was added to this reaction mixture in one portion. Stirring was continued overnight, solvent was reduced to 1/3 volume, the oily residue was dissolved with CHCl3 (25 mL), and washed twice with NaHCO3 (0.1 M, 20 mL) and H2O. The organic layer was dried with MgSO4, concentrated to dryness and coevaporated twice with toluene. The residue was dissolved in small volume of dry THF (5 mL) and treated with Et3N·3HF-Et3N (3:1). After deprotection was complete (3-4 h), the reaction mixture was diluted with CHCl3, washed twice with NaHCO3 (0.1 M), concentrated, and subjected to a silica gel column chromatography (gradient 0-4% EtOH in CHCl3, and addition of 0.05% of Et3N). The collected fractions of diastereomers were concentrated and precipitated with hexane or PE and stored as white powders. Any excess of nucleoside 11 used in coupling reactions was recovered from column as 5′,3′-OH compound (after desilylation) and was subjected to 3′-O-protection (recycling).

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Fast-(S p)-12: 31P NMR (202.46 MHz, CDCl3): δ = 100.1. 1H NMR (500 MHz, CDCl3): δ = 1.59 [t, J = 7.59 Hz, 6 H, CH(CH 3)], 1.94 (d, J = 15.61 Hz, 3 H, P-CH3), 2.10 [dq, 1 H, CH(CH3)], 2.56 [m, 1 H, CH(CH3)2], 3.44 [dd, 1 H, CH(CH3)], 3.6 [s, 3 H, (C)CH3O-C2′], 3.74 [s, 3 H, (U)CH3O-C2′], 3.80 [s, 6 H, (U)CH3O-DMT], 3.92 (m, 1 H, H5′), 4.18 [dd, J = 4.2, 2.1 Hz, 1 H, (C)H4′], 4.26 [d, J = 6.56 Hz, 1 H, (U)H2′], 5.36 [m, 1 H, (C)H2′], 5.87 [s, 1 H, (C)H1′], 6.05 [d, J = 3.41 Hz, 1 H, (U)H1′]. MS-FAB-
[M - H]: m/z calcd: 964.3; found: 962.6.
Slow-(R p)-12: 31P NMR (CDCl3): δ = 98.26. 1H NMR (CDCl3): δ = 1.59 [t, J = 7.59 Hz, 6 H, CH(CH 3)2], 1.76 (d, J = 15.32 Hz, 3 H, P-CH3), 2.10 [dq, 1 H, CH(CH3)2], 2.56 [m, 1 H, CH(CH3)2], 3.44 [dd, 1 H, CH(CH3)], 3.55 [s, 3 H, (C)CH3O-C2′], 3.74 [s, 3 H, (U)CH3O-C2′], 3.81 [s, 6 H, (U)CH3O-DMT], 3.92 [m, 1 H, (C)H2′], 4.18 [dd, J = 4.2, 2.1 Hz, 1 H, (C)H4′], 4.26 [d, J = 6.56 Hz, 1 H, (U)H2′], 5.36 [m, 1 H, (C)H2′], 5.95 [s, 1 H, (C)H1′], 6.02 (d, J = 3.43 Hz, 1 H, (U)H1′], 7.42 [d, J = 7.40 Hz, 1 H, (C)5H], 7.92 [d, J = 8.20 Hz, 1 H, (U)6H], 8.16 [d, J = 7.50 Hz, 1 H, (C)6H], MS-FAB- [M - H]: m/z calcd: 964.3; found: 962.4.