Polymer-bound oxathiaphospholane: a solid-phase reagent for regioselective monothiophosphorylation and monophosphorylation of unprotected nucleosides and carbohydrates

Two polymers bound to N,N-diisopropylamino-1,3,2-oxathiaphospholane were reacted with unprotected carbohydrates and nucleosides in the presence of 1H-tetrazole, followed by oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent. The 1,3,2-oxathiaphospholane ring-opening with 3-hydroxypropionitrile, followed by treatment with DBU, afforded the corresponding monophosphate and monothiophosphate derivatives, respectively, through the elimination of polymer-bound ethylene episulfide. Reactions using this strategy offer the advantages of high regioselectivity, monosubstitution, and facile isolation and recovery of products.     

Oxathiaphospholane Approach to the Synthesis of Conjugates of Amino Acids Methyl Esters with Nucleosides

Based upon 1,3,2-oxathiaphospholane chemistry, 5'-O-derivatization of nucleosides with the O-methyl esters of amino acids was performed and corresponding conjugates were obtained in satisfactory yield.     

Oxathiaphospholane approach to N- and O-phosphorothioylation of amino acids

A method of highly efficient synthesis of N- and O-phosphorothioylated amino acids was developed. N- and O-(2-Thiono-1,3,2-oxathiaphospholanyl)amino acid methyl esters (3) were prepared in high yields in reaction of amino acid methyl esters with 2-chloro-1,3,2-oxathiaphospholane in pyridine in the presence of elemental sulfur. Compounds 3 were converted in high yield into the corresponding methyl or benzyl phosphorothioamides 6 and 7 by DBU-assisted treatment with methanol or benzyl alcohol. When 3-hydroxypropionitrile was used instead of methanol or benzyl alcohol, the corresponding 2-cyanoethylphosphorothioamidates 4 were obtained in high yield, from which the 2-cyanoethyl group was removed with concentrated ammonium hydroxide. The oxathiaphospholane methodology was also applied for the phosphorylation of amino acids. Thus, 2-oxo-1,3,2-oxathiaphospholane derivatives 10 were prepared by oxidation of compounds 3 with SeO(2.) Compounds 10 were transformed into the corresponding phosphate diesters or amidoesters upon treatment with 3-hydroxypropionitrile in the presence of DBU. The DBU-assisted oxathiaphospholane ring-opening process in 3 and 10 did not cause any measurable C-racemization of phosphorothioylated/phosphorylated amino acids.     

An oxathiaphospholane approach to one-pot phosphorothioylation of isoprenoid alcohols

[reaction: see text] Allyl, isopentenyl, geranyl, citronellyl, farnesyl, and phytyl alcohols were transformed in good yield (>60%) into their phosphorothioates via a DBU-assisted 1,3,2-oxathiaphospholane ring-opening condensation with 2-(2-cyanoethoxy)-2-thiono-1,3,2-oxathiaphospholane, a reagent that is stable and easy to handle, followed by subsequent removal of the 2-cyanoethyl group from the intermediate phosphorothioate diester under basic conditions.     

Oxathiaphospholane approach to the synthesis of oligodeoxyribonucleotides containing stereodefined internucleotide phosphoroselenoate function

5'-O-DMT-deoxyribonucleoside-3'-O-(2-selena-4,4-pentamethylene-1,3,2-oxathiaphospholane) monomers, derivatives of dA, dC, dG, and T, can be resolved into pure P-diastereomers by silica gel column chromatography. They have been used for DBU-promoted, either solution- or solid-phase synthesis of P-stereodefined phosphoroselenoate analogues of oligodeoxyribonucleotides. Fast- and slow-eluting monomers are precursors of phosphoroselenoate internucleotide linkage of R(P) and S(P) absolute configuration, respectively. [reaction: see text]     

Stereoselective formation of a P-P bond in the reaction of 2-alkoxy-2-thio-1,3,2-oxathiaphospholanes with O,O-dialkyl H-phosphonates and H-thiophosphonates

A new method for the formation of organohypophosphates containing a P-P bond under mild conditions, based on the DBU-assisted reaction of 2-alkoxy-2-thio-1,3,2-oxathiaphospholanes with O,O-dialkyl H-phosphonates or H-thiophosphonates, has been elaborated. The resulting triesters of P(1)-thio- and P(1),P(2)-dithiohypophosphoric acids, respectively, having O-methyl or O-ethyl groups, can be selectively dealkylated to form the corresponding di- or monoesters. Appropriately protected 2'-deoxyguanosine-3'-O-(2-thio-1,3,2-oxathiaphospholane) was converted into the corresponding P(1)-thio- and P(1),P(2)-dithiohypophosphate esters in a highly stereoselective manner (98%+ and 90%+, respectively).     

Transformations of 2-(2-thiocyanatoalkoxy)-1,3,2-dioxaphospholanes

In contrast to the case of 2-(2-haloalkoxy)-1,3,2-dioxaphospholanes, the coordination of the phosphorus atom in analogous esters with an SCN group is altered under mild conditions involving the sulfur atom with formation of spirophosphoranes with a 1,3,2-oxathiaphospholane fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 950–951, April, 1991.     

Application of a solid-phase beta-triphosphitylating reagent in the synthesis of nucleoside beta-triphosphates

A beta-triphosphitylating reagent was subjected to reaction with aminomethyl polystyrene resin-bound p-acetoxybenzyl alcohol to yield the corresponding polymer-bound beta-triphosphitylating reagent. The solid-phase reagent was reacted with unprotected nucleosides (e.g., 3'-azido-3'-deoxythymidine, cytidine, thymidine, uridine, inosine, or adenosine) in the presence of 1H-tetrazole. Polymer-bound nucleosides underwent oxidation with t-butyl hydroperoxide, deprotection of cyanoethoxy groups with DBU, and the acidic cleavage, respectively, to afford only monosubstituted 5'-O-beta-triphosphorylated nucleosides.     

Solid-phase synthesis of symmetrical 5',5'-dinucleoside mono-, di-, tri-, and tetraphosphodiesters

Four classes of phosphitylating reagents were subjected to reactions with aminomethyl polystyrene resin-bound p-acetoxybenzyl alcohol to yield the corresponding polymer-bound mono-, di-, tri-, and tetraphosphitylating reagents. The solid-phase reagents were reacted with unprotected nucleosides (e.g., thymidine, adenosine, 3'-azido-3'-deoxythymidine, cytidine, or inosine) in the presence of 5-(ethylthio)-1H-tetrazole. Polymer-bound nucleosides underwent oxidation with tert-butyl hydroperoxide, deprotection of cyanoethoxy groups with DBU, and the acidic cleavage, respectively, to afford 5',5'-dinucleoside mono-, di-, tri-, and tetraphosphodiesters in 59-78% yield.     

Solid-phase reagents for selective monophosphorylation of carbohydrates and nucleosides

Two classes of aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with 2-cyanoethyl N,N-diisopropylchlorophosphoramidite to produce the corresponding polymer-bound phosphitylating reagents. These were reacted with a number of unprotected nucleosides and carbohydrates in the presence of 1H-tetrazole. Oxidation with tert-butyl hydroperoxide followed by removal of the cyanoethoxy group with 1,8-diazabicyclo[5.4.0]undec-7-ene afforded the corresponding polymer-bound phosphate diesters. Acidic cleavage of the p-acetoxybenzyl alcohol linker yielded monophosphorylated products with high regioselectivity and trapped linkers on the resins that can be reused.     

Convenient synthesis of nucleoside borane diphosphate analogues: deoxy- and ribonucleoside 5'-P(alpha)-boranodiphosphates

The nucleoside boranophosphates, having one of the nonbridging phosphate oxygens substituted with a borane (BH(3)) group, have shown potential therapeutical applications as aptamers, antisense agents, and antiviral prodrugs. An oxathiaphospholane approach, which does not require exocyclic amine protection of the nucleobase, has been successfully developed to efficiently synthesize 5'-P(alpha)-boranodiphosphates of 2'-deoxythymidine, adenosine, guanosine, and uridine. The approach involves a key intermediate, the borane complex of nucleoside 5'-O-1,3,2-oxathiaphospholane 16, that undergoes a ring-opening reaction catalyzed by 1,4-diazabicyclo[5.4.0]-undec-7-ene to form the protected nucleoside 5'-P(alpha)-boranodiphosphate 18. Treatment of 18 with ammonium hydroxide yielded diastereoisomeric mixtures of nucleoside 5'-P(alpha)-boranodiphosphates 5. This oxathiaphospholane approach ensures the availability of nucleoside 5'-P(alpha)-boranodiphosphate analogues needed for antiviral drug research.     

Selective diphosphorylation, dithiodiphosphorylation, triphosphorylation, and trithiotriphosphorylation of unprotected carbohydrates and nucleosides

[chemical reaction: see text]. Aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with diphosphitylating and triphosphitylating reagents to yield the corresponding polymer-bound diphosphitylating and triphosphitylating reagents, respectively. A number of unprotected carbohydrates and nucleosides were reacted with the polymer-bound reagents. Oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent, followed by removal of cyanoethoxy group with DBU and the acidic cleavage, respectively, afforded only one type of monosubstituted nucleoside and carbohydrate diphosphates, dithiodiphosphates, triphosphates, and trithiotriphosphates with high regioselectivity.     

Cross-coupling reactions of unprotected halopurine bases, nucleosides, nucleotides and nucleoside triphosphates with 4-boronophenylalanine in water. Synthesis of (purin-8-yl)- and (purin-6-yl)phenylalanines

An expeditious and highly efficient single-step methodology for the introduction of a phenylalanine moiety into position 8 and 6 of the purine scaffold was developed based on aqueous-phase Pd-catalysed Suzuki-Miyaura cross-coupling reactions of unprotected 4-boronophenylalanine with 8-bromo- or 6-chloropurines. The scope of the methodology was demonstrated by syntheses of unprotected (adenin-8-yl)phenylalanine base, nucleosides, nucleotides and nucleoside triphosphates as well as (purin-6-yl)phenylalanine base and nucleosides. All these products were obtained in high yields and in optically pure form.     

A Novel Protocol for the Regioselective Bromination of Primary Alcohols in Unprotected Carbohydrates or Glycosides

The regioselective and efficient bromination of primary hydroxyl groups in unprotected carbohydrates or glycosides is successfully achieved by using (chloro‐phenylthio‐methylene)dimethylammoniumchloride (CPMA) in the presence of tetrabutylammonium bromide (TBAB) in dry DMF.     

Cyclization versus oligomerization of SP- and RP-5′-OH-N-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane)s

The S_P-isomer of 5′-OH-N⁴-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane) undergoes DBU-promoted intramolecular cyclization providing as a sole product S_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate. Unexpectedly, the R_P-counterpart yields a mixture of products consisting of R_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate and macrocyclic oligo(deoxycytidine phosphorothioate)s. The results of molecular modeling indicate that the dychotomy observed for the R_P substrate may result from remarkably higher energy of the corresponding transition states, caused by the presence of bulky ‘spiro’ pentamethylene substituent at the position C4 in the oxathiaphospholane ring.     

Protection-free one-pot synthesis of 2'-deoxynucleoside 5'-triphosphates and DNA polymerization

By differentiating the functional groups on nucleosides, we have designed and developed a one-pot synthesis of deoxyribonucleoside 5'-triphosphates without any protection on the nucleosides. A facile synthesis is achieved by generating an in situ phosphitylating reagent that reacts selectively with the 5'-hydroxyl groups of the unprotected nucleosides. The synthesized triphosphates are of high quality and can be effectively incorporated into DNAs by DNA polymerase. This novel approach is straightforward and cost-effective for triphosphate synthesis.     

Bromination at C-5 of Pyrimidine and C-8 of Purine Nucleosides with 1,3-Dibromo-5,5-dimethylhydantoin

Treatment of the protected and unprotected nucleosides with 1,3-dibromo-5,5- dimethylhydantoin in aprotic solvents such as CH(2)Cl(2), CH(3)CN, or DMF effected smooth bromination of uridine and cytidine derivatives at C-5 of pyrimidine rings as well as adenosine and guanosine derivatives at C-8 of purine rings. Addition of Lewis acids such as trimethylsilyl trifluoromethanesulfonate enhanced efficiency of bromination.     

Synthesis and photophysical properties of 7-deaza-2'-deoxyadenosines bearing bipyridine ligands and their Ru(II)-complexes in position 7

The synthesis of the title 7-deazaadenine 2'-deoxyribonucleosides bearing bipyridine, phenanthroline or terpyridine ligands linked to position 7 via an acetylene or phenylene spacer is reported based on aqueous cross-coupling reactions of unprotected 7-iodo-7-deaza-2'-deoxyadenosine with ligand-functionalized acetylenes or boronic acids. The aqueous cross-coupling with acetylene or boronate building blocks containing the Ru(bpy)(3)-type of complex gave the corresponding Ru-containing nucleosides. Photophysical and electrochemical properties were studied and the most efficient type of complex was selected for future luminescent and redox labelling of DNA. The title nucleosides also showed some cytostatic and anti-HCV activities.     

Acid-Assisted Direct Olefin Metathesis of Unprotected Carbohydrates in Water

The ability to use unprotected carbohydrates in olefin metathesis reactions in aqueous media is demonstrated. By using water-soluble, amine-functionalized Hoveyda–Grubbs catalysts under mildly acidic aqueous conditions, the self-metathesis of unprotected alkene-functionalized α-d -manno- and α-d -galactopyranosides could be achieved through minimization of nonproductive chelation and isomerization. Cross-metathesis with allyl alcohol could also be achieved with reasonable selectivity. The presence of small quantities (2.5 vol %) of acetic acid increased the formation of the self-metathesis product while significantly reducing the alkene isomerization process. The catalytic activity was furthermore retained in the presence of large amounts (0.01 mm ) of protein, underlining the potential of this carbon–carbon bond-forming reaction under biological conditions. These results demonstrate the potential of directly using unprotected carbohydrate structures in olefin metathesis reactions under mild conditions compatible with biological systems, and thereby enabling their use in, for example, drug discovery and protein derivatization.     

Preparation of highly substituted 6-arylpurine ribonucleosides by Ni-catalyzed cyclotrimerization. Scope of the reaction

Transition metal complex catalyzed cocyclotrimerization of protected alkynylpurine ribonucleosides 1 with various diynes 2 gave rise to a series of 6-arylpurine nucleosides 3 that were further deprotected to free nucleosides 4. Generally, the best yields of cyclotrimerizations were obtained with a catalytic system Ni(cod)2/2PPh(3). On the other hand, CoBr(PPh(3))3 proved to be a superior catalyst for cyclotrimerization of 1 with dipropargyl ether 2g. In addition, Ni catalysis is also suitable for direct cyclotrimerization of unprotected alkynylpurine ribonucleosides 5 to the corresponding 6-arylpurinylribosides 4.