Phosphorothioates chiral synthesis

Chirahty at the phosphoms is an unavoidable problem in all phosphorothioate syntheses. The phosphoramidite method produces a mixture of both the and the diastereomers having a small excess of the isomer (53). Although some progress has been made in the chiral synthesis of dinucleoside phosphorothioates, low yields have limited the utility of these approaches. The chiral center may be eliminated by replacing the other, nonbridging oxygen with sulfur. Avoidance of the chirahty problem is one reason for the interest in phosphorodithioates. 

Stec, W. J., Grajkowski, A, Koziolkiewicz, M., and Uznanski, B. (1991) Novel route to oligo(deoxyribonucleoside phosphorothioates. Stereocontrolled synthesis of P-chiral oligo(deoxyribonucleoside phosphorothioates) Nucl. Acids Res.l9,5883-5888. 

With regard to the phosphorus stereochemistry, a new stereospecific synthesis of chiral 0,0-dialkyl thiophosphoric acids (6,7) has been developed which is based on the Horner-Wittig reaction of the optically active phosphonothionate carbanions containing the sulfoxide or dithioacetal moieties. The transformation of (R)-(+) 0-methyl 0-isopropyl methanephosphonothionate (10)(8) into (R)-(-) 0-isopropyl phosphorothioic acid (H) best Illustrates this method. 

The chiral y-[l80]phosphorothioate of ATP, (Pp)-ATPyS, yl80(/3, y)lsO, was synthesized by the procedure outlined in Fig. 8 [25]. (Sp)-ADPaS, alsO(a,/3)l80 was prepared by stereospecific phosphorylation of AMPaS, al802 using the adenylate and pyruvate kinase system followed by dephosphorylation with glucose and hexokinase. This was the starting material for the synthesis, with the chiral a-... 

Phosphorothioate and boranophosphate linkages introduced into DNA or RNA using nucleoside 5 -[a-thio]triphosphates and nucleoside 5 -[a-borano]tri-phosphates are more resistant to exo- and endonucleases than normal 3, 5 phosphodiester linkages. Combination of the two modifications yielded a novel non-bridging-disubstituted chiral a-triphosphate nucleoside, namely the thymidine 5 -[a-P-borano, a-P-thio] triphosphate (119). The synthesis was the modification of a procedure developed for the synthesis of nucleoside triphosphates and previously reported by the group. 

The 2-oxo analogues of dithiaphospholanes 81, namely appropriately protected nucleoside 5 -0- (83a) or 3 -0-(2-oxo-l,3,2-dithiaphospholanes) (83b) have also been used as P-prochiral substrates for the potentially asymmetric synthesis of dinucleotides with P-chiral phosphorothioate internucleotide linkage (85, X=0) (Scheme 21, path b). For example, reaction of 5 -0-DMT-thymi-dine-3 -0-(2-oxo-l,3,2-dithiaphospholane) (83b) with NMsobutyryl-3 -0-acetyl deoxyguanosine in the presence of DBU provided corresponding dinucleoside 3, 5 -phosphorothioate of isomeric composition RP/SP=28/72 [110]. 

Stec extended his work on P-chiral phosphorothioates and described the synthesis of P-chiral, isotopomeric deoxyribonucleoside-phosphorothioates and -phosphates (76a-p) labelled with an oxygen isotope. To obtain stereodefined PS 0-oligos, the 5 -0-DMT-nucleoside-3 -0-(2-thio- spiro -4,4-pentamethy-lene-l,3,2-[0 ]oxathiaphospholanes were synthesised by phosphitylation of the correct protected nucleoside with chirally pure [O ]oxathiaphospholane, with subsequent sulfurisation. The resulting oxadithiaphospholanes were separated by chromatography into diastereomerically pure forms and individually treated with Se02 to yield the oxathiaphospholanes. ... 

Description of the synthesis of phosphodiesters (prochiral phosphorus center) is beyond the scope of this chapter. Only the chemical synthesis of chiral phos-phomonoesters (4-6) and chiral inorganic phosphates (7) are discussed. The chiral phosphates or chiral phosphorothioates obtained from enzyme reactions are not described in this section. 

Lowe, Cullis, and co-workers have described general methods for the synthesis of oxygen chiral phosphorothioate monoesters (see Figs. 3 and 4). The synthesis by Cullis is strictly analogous to the synthesis of chiral phosphate monoesters by Knowles except that (- )-ephedrine is thiophosphorylated with PSCI3... 

Figure 13. Synthesis of chiral phosphorothioates. Modified from [77,78].

Figure 14. Synthesis of chiral phosphorothioates by ring opening of 1,3,2-oxathiaphospholanes. Modified from [79, 80],...

Phosphorothioates can be incorporated into DNA sequences by solid-phase synthesis techniques. The chemical synthesis of the monomer imits creates a chiral center at the modified phosphorous atom. These diastereomers can be separated for chemical synthesis, while any enzymatic incorporation results in only the... 

A full account of an earlier paper (Vol. 25, p. 217, ref. 125) on the preparation of iL-chiro-inositol 2,3,5-triphosphate from L-quebrachitol and the synthesis of L-chiro-inoatol 1,4,6-triphosphate and the corresponding triphosphorothioate also from L-quebrachitol has been reported. Also, a full account (Vol. 23, p. 186, ref 70) on the preparation of racemic /nyo-inoatol 1,4,5 triphosphate and 1,4-bisphosphate-5-phosphorothioate has been reported as well as the preparation of phosphorylated intermediates for the nthesis of both chiral and racemic myo-inoatol 1,43-triphosphate and its phosphorothioate analogue. ... 

Lesnikowski, Z J and Jaworska, M M (1989) Studies on stereospecific formation of p-chiral internucleotide linkage. Synthesis of (Rp,Rp)-annitro-benzyl group as a new S-protection Tetrahedron Lett. 30,3821-3824... 

The discovery of antiviral activity of oligo(nucleoside methane-phosphonate)s (44) and oligo(nucleotide phosphorothioate)s (45-47), so far chemically prepared by the nonstereocontrolled methods, attracted the attention of several research establishments to the search for stereospecific synthesis of those classes of oligonucleotide analogs. Since their routine synthesis via phosphoramidite or any other approach leads to the mixture of m diastereoisomers, the question may be asked whether desired antiviral activity is owing to all m components of diastereo-isomeric mixture or to the fraction possessing the proper sense of chirality at each modified phosphate. Moreover, since the seminal works of... 

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