AU697710B2

AU697710B2 - Oxidation of phosphorus compounds

Info

Publication number: AU697710B2
Application number: AU73122/96A
Authority: AU
Inventors: Judith Elizabeth Browne; Michael John Driver
Original assignee: Biocompatibles Ltd
Current assignee: Abbott Vascular Devices Ltd
Priority date: 1995-10-16
Filing date: 1996-10-16
Publication date: 1998-10-15
Anticipated expiration: 2016-10-16
Also published as: WO1997014702A1; CN1202898A; AU7312296A; CA2233160A1; EP0863908A1; KR19990064280A; JPH11513682A

Description

Oxidation of Phosphorus Compounds

The present invention relates to a process in which a phosphite triester compound is oxidised to form the corresponding phosphate triester derivative, that is a phosphorus V compound. The process uses a tertiary amine oxide as oxidant and the tertiary amine byproduct is used as a reactant in a subsequent step such as removal of a protecting group or displacement of a halogen atom.

There are various synthetic processes in which phosphite ester compounds are oxidised so as to produce a corresponding phosphorus V compound. For instance, various synthetic processes starting with phosphorous trichloride as starting material pass through phosphite ester intermediates in a multi-step process to form phosphate ester products. Such processes are used in the synthesis of phospholipid derivatives, glycolipid derivatives and nucleic acids. Cyclic diesters, such as 1,3,2- dioxaphospholanes and 1,3,2-dioxaphosphorinanes may be oxidised to form the corresponding 2-oxo derivatives. Edmundson et al, in Che . and Ind (1966) 1828 to 1829 describe the use of molecular oxygen in benzene as a successful oxidising agent, especially for phospholanes. Dinitrogen tetroxide had also been used as an oxidising agent.

In nucleic acid synthesis a phosphite triester is generally oxidised using aqueous iodine in the presence of pyridine or 2,6-lutidine to form the corresponding phosphate triester. Iodine cannot be used in non aqueous systems and so is of no use for oxidising phosphorus III compounds which have substituents which are sensitive to water. For instance it would be of no use for oxidising a phospholane or phosphorinane compound such as those described by Edmundson op. c±t .

Other oxidising agents have been described for oxidising phosphite ester compounds in nucleic acid synthesis, some of which may be used in non-aqueous solvent systems. Examples of non-aqueous oxidising agents used in nucleic acid synthesis include dinitrogen tetroxide, tertiary-butyl hydroperoxide, ditertiary-butyl hydroperoxide, cumene hydroperoxide, hydrogen peroxide, bis-(trimethylsilyl) peroxide in the presence of catalytic amounts of trimethylsilyl triflate, m-chloroperbenzoic acid, dimethyl sulphoxide, trimethyla ine N-oxide, pyridine-N-oxide, N-methylmorpholine-N-oxide, iodobenzene diacetate, tetra-n-butylammonium periodate and oxygen in the presence of free radical generators. However aqueous iodine continues to be the reagent of choice for the oxidation of nucleotide phosphite triesters.

Noyori and colleagues in Tet.Lett (1986) 27(35),4191- 94, (Hayakawa et al) described various non-aqueous oxidation processes for phosphite triesters, including the amine oxide compounds, trimethylamine N-oxide, N-

- methylmorpholine-N-oxide and pyridine-N-oxide. The yields with the first and third mentioned amine oxides were extremely low, even after long reaction times. The yield with the second mentioned compound was reasonable. It would be desirable to provide a process in which amine oxides are used as oxidising agents which will give a high phosphate yield. In Bull.Soc.Chim.Fr. (1974) issue 3-4, 677-680 Branlt and Chabrier describe the oxidation of cyclic phosphite triesters and the subsequent silultaneous fing opening and amination of the corresponding phosphate triester to form phosphoryl choline derivatives. The phosphite triester is a diester of optionally substituted cathylene glycola or 1,3-propandiol with the third al oxy group being selected from ethoxy, 0-acetylphenoxy, phenoxy and methoxy. The oxidising agent is trimethyla ineoxide. In C.R. Acad.Sci.Paris, Ser C (CHDCAQ) (1973), 276 (13), 1135-7, Chabrier and Branlt there is a further disclosure of the oxidation of various mono methoxy cyclic phosphite triesters using tertiary amine oxide. In a new process according to the present invention for forming phosphotriester compounds: a phosphite triester of the formula I

BR⁷0 - P - OR⁴ I ₅ I

OR

in which R is a straight or branched alkylene, oxoalkylene or oligo-oxaalkylene chain and B is an ethylenically unsaturated poly erisable group selected from

wherein:

R is hydrogen or a C.--C,, alkyl group; g a

A is -O- or -NR - where R is hydrogen or a C_|-C₄ alkyl group; and

K is a group -(CH₂)_pOC(0)-, -(CH₂)_pC(O)0-,

-(CH₂)_pOC(0)0-, -(CH₂)_pNR⁹-, - (CH-) _pOC (O) NR⁹- ,

-(CH₂) NR C(0)NR -, (in which the groups R are the same or different) , -(CH₂)_pO-, -(CH₂) S0₃ -, or a valence bond and p is from 1 to 12 and R is hydrogen or a C₁-C₄ alkyl group; and

R 4 and R5 are the same or different and each is selected from C₁.₄₀ straight or branched-alkyl groups, - alkenyl groups and -alkynyl groups, any of which may be unsubstituted or substituted by aryl groups, hydroxyl groups, halogen atoms, amine (including mono-, di- or tri- alkyl substituted amine) groups, sulphonium, thiol, carboxylic acid or phosphoniu groups, or R 4 and R5 may, together, with the oxygen atoms to which they are attached and the phosphorus atom form a 5 to 15 membered heterocyclic ring, optionally containing additional hetero atoms and/or substituents at ring carbon and/or nitrogen atoms (if any) , is oxidised in solution by an oxidising agent to form the corresponding phosphate triester of the formula II

are as defined for formula I. Although it may be possible to use conventional oxidising agents such as have been used in the prior art for oxidising phosphite triesters and are mentioned in the above prior art discussion, we have found that some of these attack the ethylenic bond in the group B. Thus, in a preferred aspect, the oxidising agent is a tertiary amine oxide Z → O, whereby the corresponding tertiary amine Z is produced as a byproduct. This allows the compound of the formula II and the tertiary amine to be reacted together in a subsequent step to produce a compound of the formula III

- BR⁷0 - P - OR⁶ III

in which R is as defined above for formula I, Y is -θ^" or OH and R 6 i.s ei.ther R4 or, where R5 and R4 together with the oxygen and phosphorus atoms to which they are attached, are joined to form a heterocyclic ring in the compound of the formula II and Y is -θ^' or OH in the compound III, is a group +ZR5R - in which R4R5 represent the groups as defined for compound of the formula II and Z is as defined in the tertiary amine oxide above provided that R is not R when Y is OR⁵.

In this aspect of the process the tertiary amine oxide which is used as the oxidising agent for the phosphite triester may be any suitable tertiary amine oxide. Examples of suitable amine oxides are trialkylamine oxides in which the alkyl groups are each lower alkyl, for instance trimethylamine-N-oxide or may be a heterocyclic amine, for instance based on an unsaturated heterocyclic ring such as a pyridine ring, or a saturated ring system such a N-lower alkyl morpholine ring. The tertiary amine oxide may therefore be pyridine-N-oxide or N-methyl morpholine-N-oxide. Preferably the tertiary amine oxide is trimethylamine-N-oxide.

The two step process of the preferred embodiment of the present invention allows the oxidised intermediate produced in situ immediately to be further reacted with the byproduct of the oxidation reaction in a further step. The further step may be a base catalysed deprotection step, in which a protecting group R is removed from the phosphate. Alternatively, the reaction may be an amination reaction,

₄ for instance, of a halo-substituted alkyl group R to produce the corresponding quaternary ammonium compound. In a further example, the tertiary amine is used in a simultaneous deprotection and amination reaction where the groups R 4 and R5 are j.oi.ned to one another to form a heterocyclic ring with the oxygen atoms to which they are attached and the phosphorus atom, thereby forming a ring

- opened phosphate diester in which the group R contains a quaternary ammonium group (i.e. is a group R 4R5Z+). In any of such subsequent steps, it may be desirable to include additional tertiary amine reactant, which is usually the same as the tertiary amine byproduct. It may also be desirable to add additional solvent and/or to remove some or all of the solvent from the first step. Preferably, however, no solvent is removed after the first step.

R is preferably unsubstituted lower alkyl or halogen- substituted lower alkyl, or together with R forms a 5-7- membered ring. In the present invention the group R is preferably a C₁.₆ alkyl group or an aryl group, preferably substituted with one or more electron withdrawing groups, such as halogen atoms, nitro groups, cyano groups, sulphonyl groups, and aryl (including heteroaryl) groups. Substituents in R may additionally provide steric hindrance (for instance 1,1-dialkyl substituents on an alkyl group) . Although R may represent a methyl group, it preferably represents a lower alkyl group with an electron withdrawing substituent such as an aryl group, a cyano group or a vinyl group. Preferred groups R⁵ are allyl, benzyl, phenyl, phenylsulphoethyl, methyl-sulphoethyl, para-nitrophenylethyl, 2,2,2-trihaloethyl (especially trichloro- and tribromo-ethyl) , 2,2,2-trihalo-l,1,- dialkylethyl (especially 2 , 2 , 2 , -trichloro-1, 1- dimethylethyl, 2'-and 4'-pyridylethyl, jπ- ethylbenzyl, p- or m-halobenzyl, m,p-dichlorobenzyl, pentahalophenyl (especially pentafluoro- and pentachloro-phenyl) 2,6- dimethylphenyl and 2, -dinitrophenyl and, most preferably, beta-cyano ethyl. In another preferred aspect of the invention the group R 5 i.s joined to the group R4 to form an ethylene or higher poly(methylene) group. R is preferably unsubstituted lower alkyl (C,^ - alkyl) or halogen substituted lower alkyl. Alternatively

R and R together are ~(CH₂)₂.₆-, preferably -(CH₂)₂-.

In the compound of the formula I B is preferably a group of the formula CH₂=C(R)-CO-A-. Preferably R is hydrogen or methyl, preferably methyl. A may be -NR -, but is preferably -0-. R is preferably -(CH₂)₂.₆-, preferably

—CH₂—CH —•

Suitable solvents for the oxidation step include nitrile derivatives of lower carboxylic acids, especially acetonitrile, and other aprotic solvents such as dimethyl forma ide and dimethyl acetamide. The use of acetonitrile, where the oxidising agent is tertiary amine oxide is found to give excellent yields and low levels of by product formation which is surprising especially in view of the observation by Hayakawa et al (op cit) that such solvents give poor results.

Suitable solvents for a step of the process following the oxidation step are acetonitrile, as well as mixtures of acetonitrile and dichloromethane, methanol/chloroform mixtures or even aqueous lower alcohol mixtures.

The invention is illustrated further in the following examples. Examples 3 to 5 show the use of oxidising agents other than tertiary amine oxide in the first step of the process. These show that the rate of the oxidation step of the preferred embodiment of the present invention using amine oxide and its yields are comparable to those using commonly used non-aqueous oxidising agents, meta-chloroperbenzoic acid, dinitrogen tetroxide and tertiary butyl hydroperoxide. The results also show that the use of amine oxide oxidising agents in the preferred embodiment of the present invention facilitates further reaction steps and precludes the need to isolate reaction intermediates. Example l

Large scale preparation of 2-(methacryloyloxyethyl)-2'- trimethylammoniumethyl) phosphate, inner salt 1.1 N.N-Diisopropylaminoethylene phosphite

Diisopropylamine (463 g, 4518 mmol) was added dropwise over one hour to a stirred solution of 2-chloro-l,3,2- dioxaphospholane (distilled, 115.8 g, 915 mmol) in anhydrous ether (4000 ml) at -10°C under nitrogen. The mixture was allowed to return to room temperature and was stirred for 16 hours, filtered to remove diisopropylammonium chloride and the filter bed washed with ether (400 ml) . The filtrate and washings were evaporated to ca 500 ml and the mixture was refiltered and the filter bed was washed with ether (1400 ml) . The solvent was removed to give a mobile liquid which was filtered through a sinter funnel and fractionally distilled (40°C, 0.1 mbar) to give pure N,N-diisopropylaminoethylene phosphite , 104.2 g, 545 mmol, 60% yield. H-nmr , 200 MHz , ( CDC1₃) δ 1 . 17 (d) , 3 . 46 (m) , 3 . 89 (m) , 4 . 14 ( )

1.2 2- r (Methacryloyl) ethyloxy") -1.3 , 2 -dioxaphospholane

A mixture of 4,5-dichloroimidazole (70 g, 511 mmol) and 2- hydroxyethyl methacrylate (68.0 g, 523 mmol) was dissolved in dry acetonitrile (500 ml) . N,N-Diisopropylaminoethylene phosphite (100 g, 523 mmol ) in dry acetonitrile (100 ml) was added dropwise over one hour under a nitrogen atmosphere at room temperature and was then stirred for ten

__ inutes. The mixture was filtered through a tightly packed bed of Celite and the pad was washed with acetonitrile (200 ml) to give a solution of 2-[ (methacryloyl)ethyloxy] - 1,3,2-dioxaphospholane which was used immediately.

1.3 2-r (Methacryloyli ethyloxyl -2-oxo-l.3.2- dioxaphospholane

The solution of 2-[ (methacryloyl)ethyloxy]-1,3,2- dioxaphospholane in acetonitrile (800ml) was cooled to - 10°C and a solution of anhydrous trimethylamine-N-oxide (35.4 g, 471 mmol) in acetonitrile (200 ml) was added dropwise under nitrogen over 90 minutes. The mixture was allowed to warm to room temperature and the solvent was evaporated to ca 800 ml to give a solution of 2- [ (methacryloyl) ethyloxy ] -2-oxo-l , 3 , 2-dioxaphospholane which was used immediately . A sample was analysed by H-nmr.

¹H-nmr , 200 MHz , (CDC1₃) <S = 1. 97 (s) , 4 . 43 (m) , 5. 66 (s) , 6.21 (s)

Tic of the product showed it to be clean with few by products apparent.

1.4 2-(Methacryloyloxyethyl)-2 '-trimβthylammoniumethyl) phosphate, inner salt

The solution of 2-[ (methacryloyl)ethyloxy]-2-oxo-l,3,2- dioxaphospholane was treated with trimethylamine (49.9 g, 845 mmol) in dry acetonitrile (200 ml) and stirred at 50°C for 16 hours. The mixture was cooled to ambient temperature and some of the excess trimethylamine was removed under reduced pressure. The solution was warmed to 80°C, filtered through a bed of Celite under nitrogen . After cooling a total of 300 ml of acetonitrile was removed under reduced pressure, and the solid was isolated after crystallisation to give pure 2-(methacryloyloxyethyl)-2'- trimethylammoniumethyl) phosphate, inner salt, 35.0 g, 119 mmol, 23 % yield from 2-hydroxyethyl methacrylate.

'H-nmr, 200 MHz, (D₂0) ό^" = 1.94 (s) , 3.21 (s) , 3.66 (m) , 4.17 (m) , 4.31 ( ) , 4.39 (m) , 5.76 (s) , 6.19 (s)

13 C-nmr, 50.1 MHz, (D₂0) δ - 20.2, 56.8, 62.3, 66.7, 67.3, 68.8, 129.9, 138.7, 172.4 Example 2

2-f(Mβthacryloyl)ethyloxy1-1,3.2-dioxaphospholane

and 2-hydroxyethylmethacrylate (6.8 g, 52.3 mmol) was dissolved in dry acetonitrile (100 ml) . N,N- Diisopropylaminoethylene phosphite (10 g, 52.3 mmol) was added under a nitrogen atmosphere at room temperature and stirred for ten minutes. The mixture was filtered through a tightly packed bed of Celite and the pad was washed with acetonitrile (ca 20 ml) to give a solution of 2- [ (methacryloyl)ethyloxy] -1,3,2-dioxaphospholane which was used immediately.

-'Hnmr, 200 MHz, (CDC1₃) δ = 1.97(s), 4.01(m), 4.25(m),

5.62(s) , 6.20(s)

2-r (Methacryloyl)ethyloxy!-2-oxo-l.3.2-dioxaphospholane

The solution of 2-[ (methacryloyl)ethyloxy] -1,3,2- dioxaphospholane in acetonitrile (25 ml) was cooled to 0°C and a solution of trimethylamine-N-oxide (3.54 g, 47.1 mmol) in acetonitrile (10 ml) was added dropwise under nitrogen. The mixture was allowed to warm to room temperature to give a solution of 2- [ (methacryloyl)ethyloxy]-2-oxo-l,3,2-dioxaphospholane which was used immediately. A sample was analysed by H-nmr.

¹H-nmr, 200 MHz, (CDC1₃) δ = 1.96(s), 4.43(m), 5.63(s), 6.21(s) Tic of the produce showed it to be clean , without significant by products .

2 - (Methacryloyloxyethyl ) -2 ' trimethylammoniuaethyl ) hosphate, inner salt

The solution of 2-[ (methacryloyl)ethyloxy]-2-oxo-l,3,2- dioxaphospholane was treated with trimethylamine (4.64 g, 78.0 mmol) in dry acetonitrile (20 ml) and stirred at 50°C for 48 hours. The mixture was cooled to ambient temperature and evaporated to about half its volume. The mixture was cooled to -20°C for 16 hours. The mixture was filtered through filter paper under nitrogen and washed with acetonitrile (13 ml) . The solid was isolated after

- crysallisation to give pure 2-(Methacryloyloxyethyl)-2'- trimethyl-am oniumethyl) phosphate, inner salt, 4.16 g, 14.1 mmol, 27% yield from 2-hydroxyethyl methacrylate.

¹H-nmr, 200 MHz, (D₂0) δ = l.94(s), 3.21(s), 3.67(m) , 4.17(m) , 4,30(m) , 4.39(m) , 5.75(s), 6.19(s) .

A second crop of material was crystallised which was purified by column chromatography on silica (150 g) , eluting with ethanol to give pure material, 3.87g, 13.0 mmol, 25% yield from 2-hydroxyethyl methacrylate.

¹H-nmr, 200 MHz, (D₂0) δ = 1.93(s), 3.19(s), 3.64(m), 4.14(m), 4.29(m), 4.39(m), 5.74(s), 6.19(s)

Total yield (based on 2-hydroxyethylmethacrylate) was 52%. Rvample 3

2 - (Methacryloγloxyethyl ) -2 ' -trimethylam oniumethyl ) phosphate, inner salt usinσ metachloroperbenzoic acid oxidant

2-Hydroxyethylmethacrylate (0.43 g, 3.32 mmol) and 4,5- dichloroimidazole (0.45 g, 3.32 mmol) were stirred in dry acetonitrile (10 ml) in the presence of 4A molecular sieves (1 g) . Bis(diisopropylamino)-cyanoethylphosphine (1 g, 3.32 mmol) was added to the mixture which was stirred under nitrogen at room temperature for 4 hours to give the crude monophosphoramidite.

'H-nmr, 200 MHz, (CDC1₃) ό" = 1.18 (d) , 1.94 (s) , 2.62 (t) , 3.60 (m) , 3.84 (m) , 4.30 (t) , 5.60 (s) , 6.14 (s)

Bromoethanol (redistilled, 0.41 g, 3.32 mmol), 4,5- dichloroimidazole (0.45 g, 3.32 mmol) and 4A molecular sieves (l g) were added to the reaction mixture and stirred at room temperature for 16 hours. A further quantity of bromoethanol (redistilled, 0.05 g, 0.40 mmol) was added and the mixture was stirred at 40°C for four hours. After filtering through celite and a 0.2 μm glass fibre filter, the solvent was removed to give crude triphosphite.

¹H-nmr, 200 MHz, (CDC1₃) <5 = 1.43 (d) , 1.94 (s) , 2.68 (t) , 3.50 (t) , 4.11 (m) , 4.34 (t) , 5.62 (s) , 6.17 (s)

The crude triphosphite was dissolved in dichloromethane (20 ml) and treated with meta-chloroperbenzoic acid (0.57 g, 3.32 mmol) and stirred at room temperature for ten minutes. The solution was extracted with saturated aqueous sodium bicarbonate ( 4 x ca 20 ml) . The combined aqueous layers were back extracted with dichloromethane (ca 40 ml) which was pooled with the earlier organic fraction and re- extracted with saturated aqueous sodium bicarbonate ( 2 x ca 20 ml) . The mixture was dried over magnesium sulphate and evaporated to give the crude triphosphate, 1.18 g, 3.19 mmol, 96% yield from 2-hydroxyethyl methacrylate.

H-nmr, 200 MHz, (CDC1₃) <5 = 2.00 (s) , 2.80 (t) , 3.54 (t) , 4.37 ( ) , 5.65 (s) , 6.19 (s)

Tic of the product showed significant by products, believed to be due to by products in which the oxidising agent attacks the ethylenically unsaturated group. Thus the product is not as clean as when using the amine oxide oxidising agent.

The crude triphosphate (1.18 g, 3.19 mmol) was dissolved in dry acetonitrile (ca 30 ml) and treated with trimethylamine (1.57 g, 26.5 mmol) in a sealed vessel and heated at 75°C for 48 hours. 4A molecular sieves (1.5 g) were added to the mixture and heating was maintained for a further two hours before filtering through celite and a 0.2 μ glass fibre filter . The solvent was evaporated and the residue dissolved in methanol and purified by column chromatography on silica gel (ca 20 g) eluting with methanol. Fractions containing product were combined and evaporated to dryness to give pure 2- (methacryloyloxyethyl) -2 ' - (trimethylammoniumethyl) phosphate, inner salt, 0.29 g, 0.97 mmol, 30% yield.

¹H-nmr, 200 MHz, (D₂0) <S = 1.96 (s) , 3.23 (s) , 3.67 (m) , 4.17 (m) , 4.31 (m) , 4.40 (m) , 5.76 (s) , 6.20 (s)

The overall yield of 2-(methacryloyloxyethyl)-2'- trimethylammoniumethyl) phosphate, inner salt from 2- hydroxyethylmethacrylate was 29%.

Example 4

2 - r (Methacryloyl) ethyloxyl -2-oxo-l . 3 .2 -dioxaphospholane using dinitroσen tetroxide oxidisinσ agent

o Dinitrogen tetroxide was purified using the method of MS Anson and C McGuigan (J. Chem. Soc. Perkin Trans. 1, 1989, 715). A solution of dinitrogen tetroxide (0.175 g, 1.92 mmol) in dry dichloromethane (12 ml) was added dropwise to a solution of 2-[ (methacryloyl) ethyloxy]-1,3,2- dioxaphospholane (produced as in example 1.2) (1.69 g, 7.68 mmol) in dry dichloromethane at -60°C. After leaving for five minutes the mixture was allowed to warm to room temperature and the solvent was evaporated to give crude 2- [ (methacryloyl)ethyloxy]-2-oxo-l,3,2-dioxaphospholane (1.86 g, 7.8 mmol) which was used immediately (for example in a step corresponding to example 1.4).

H-nmr, 200 MHz, (CDC1₃) δ = 1.97 (s) , 4.44 ( ) , 5.63 (s) , 6.21 (s)

Tic of the product showed it was less clean than that of examples 1 and 2.

Example 5

2-r (Methacryloyl)ethyloxy1-2-oxo-l.3.2-dioxaphospholane using t-butyl hydroperoxide oxidising agent

A solution of tert-butylhydroperoxide in decane (5.5 M, 1.40 ml, 7.68 mmol) in dry dichloromethane (15 ml) was added dropwise to a solution of 2-[ (methacryloyl)ethyloxy] -1,3,2-dioxaphospholane (1.69 g, 7.68 mmol) (produced in example 7.2) in dry dichloromethane (15 ml) at 0°C. After leaving for five minutes the mixture was allowed to warm to room temperature and the solvent was evaporated and the residue dried under vacuum to give crude 2- [ (methacryloyl)ethyloxy]-2-oxo-l,3,2-dioxaphospholane which was generally used immediately (for instance for a step corresponding to example 1.4).

'H-nmr, 200 MHz, (CDC1₃) δ = 1.97 (s) , 4.46 (m) , 5.63 (s) , 6.21 (s)

Tic of the product showed it was less clean than that of examples 1 and 2.

Byaw e fi Preparation of 2 - ( meth crv 1ov1oxyβthv 1 ) - 2 ' (trimethγlamoniumethyl) hosphate inner salt

A solution of 2-chloro-l, 3,2-dioxaphospholane (4.9g, 0.04M) in acetonitrile was cooled to -10°C under a nitrogen atmosphere when 2,6 - dimethylpyridine (4.0g, 0.04M) was added over 20 minutes. The mixture was stirred at -10°C for a further 20 minutes. A solution of 2-hydroxyethyl methacrylate (4.4g, 0.033M) in acetonitrile (8ml) was added

- over 15 minutes at -10^CC. The mixture was allowed to warm to 0°C and was filtered. The filtrate was cooled to -10°C and treated with a solution of trimethylamine N-oxide (2.4g, 0.32M) in acetonitrile (25ml). A solution of trimethylamine (3.3g) in acetonitrile (10ml) was added. The mixture was heated in a closed system at 45°C for 16 hours to give the desired product which was isolated by concentrating the reaction mixture and crystallisation at 0°C.

Tic showed that the product was clean and contaminated by low quantities of by products. 'H-nmr, 200 MHz, (D₂0) δ = 1.94 (s) , 3.21 (s) , 3.66 ( ) , 4.17 (m) , 4.31 (m) , 4.39 (m) , 5.76 (s) , 6.19 (s)

¹³C-nmr, 50.1 MHz, (D₂0) δ = 20.2, 56.8, 62.3, 66.7, 67.3,

68.8, 129.9, 138.7, 172.4

°γ

Claims

1. A process of forming phosphotriester compounds wherein: a phosphite triester of the formula I

in which R is a straight or branched alkylene, oxoalkylene or oligo-oxaalkylene chain and B is an ethylenically unsaturated polymerisable group selected from

wherein:

R is hydrogen or a C,-^ alkyl group; A is -O- or -NR 8- where R8 is hydrogen or a C^-C^ alkyl

- group; and

K is a group -(CH₂)_pOC(0) -, -(CH₂)_pC(0)0-,

-(CH₂)_p0C(0)0-, -(CH₂)_pNR⁹-, - (CH₂) _pOC (O) NR⁹- ,

-(CH₂)_pNR9C(0)NR9-, (i.n whi.ch the groups R9 are the same or different), -(CH₂)_pO-, -(CH₂) S0₃ -, or a valence bond and p is from 1 to 12 and R 9 is hydrogen or a C,-^ alkyl group; and

R 4 and R5 are the same or different and each is selected from C,_₄₀ straight or branched-alkyl groups, - alkenyl groups and -alkynyl groups, any of which may be unsubstituted or substituted by aryl groups, hydroxyl groups, halogen atoms, amine (including mono-, di- or tri- alkyl substituted amine) groups, sulphonium, thiol, carboxylic acid or phosphonium groups, or R 4 and R5 may, together, with the oxygen atoms to which they are attached and the phosphorus atom form a 5 to 15 membered heterocyclic ring, optionally containing additional hetero atoms and/or substituents at ring carbon and/or nitrogen atoms (if any) , is oxidised in solution by an oxidising agent to form the corresponding phosphate triester of the formula II

O

in which R 7, B, R4 and R5 are as defined for formula I.

2. A process according to claim 1 characterised in that the oxidising agent is a tertiary amine oxide Z -* O, whereby the corresponding tertiary amine Z is produced as a byproduct. . A process according to claim 2 in which the compound of the formula II and the tertiary amine by product are reacted together in a subsequent step to produce a compound of the formula III

O

in which B and R are the same groups as in the compound of the formula II, Y is -O^* or OH or OR , in which R is as defined in claim 1, and R is either R or, where

R 5 and R4 together with the oxygen and phosphorus atoms to which they are attached, are joined to form a heterocyclic ring in the compound of the formula II and Y is -o^" or OH in the compound III, is a group ⁺ZR⁵R⁴- in which R⁴R⁵ represent the groups as defined for compound of the formula

II and Z is as defined in the tertiary amine oxide above, provided that R is not R⁴ when Y is OR⁵.

4. A process according to claim 3 in which the said subsequent step comprises a base-catalysed deprotection step in which a protecting group OR⁵ is replaced by o^" or OH (ie Y is θ^' or OH) .

5. A process according to claim 3 or claim 4 in which the said subsequent step comprises an amination reaction in which a compound II in which R⁴ represents a halo-alkyl group is reacted to substitute an ammonium group for the halogen atom.

6. A process according to claim 3 in which R⁴ and R are joined to one another to form a heterocyclic ring with the oxygen atoms to which they are attached and the phosphorous atom and in which the said subsequent step is a simultaneous ring opening and amination reaction which produces a compound III in which R is a group RRZ^*.

7. A process according to any of claims 3 to 6 in which the solvent for the oxidation step and for the said subsequent step is the same, and is preferably acetonitrile.

8. A process according to any of claims 2 to 7 in which Z -♦ O is a trialkylamine oxide, preferably in which each alkyl group is lower alkyl, or a saturated or unsaturated heterocyclic amine oxide, preferably pyridine-N-oxide or N- lower alkyl morpholine-N-oxide, most preferably being -trimethylamine-N-oxide.

9. A process according to any preceding claim in which R is a C₁.₆ alkyl group or an aryl group preferably substituted with one or more electron withdrawing groups, such as halogen atoms, nitro groups, cyano groups, sulphonyl groups, and aryl (including heteroaryl) groups.

10. A process according to claim 9 in which R is selected from allyl, benzyl, phenyl, phenylsulphoethyl, methyl- sulphoethyl, para-nitrophenylethyl, 2,2,2-trihaloethyl (especially trichlorol-and tribromo-ethyl) , 2,2,2-trihalo- 1,1,-diaIky1ethyl (especially 2,2,2,-trichloro-l,1- dimethylethyl, 2'-and 4'-pyridylethyl, jji-methylbenzyl, p-or m-halobenzyl, ra,p-dichlorobenzyl, pentahalophenyl (especially pentafluoro- and pentachloro-phenyl) 2,6- dimethylphenyl and 2,4-dinitrophenyl and, most preferably, beta-cyano ethyl.

11. A process according to any preceding claim wherein B is a group of the formula

R 0

CH₂ = C I-CII-A- in which R is hydrogen or methyl, preferably methyl and A is preferably -0-; and

R is (CH₂)₂.₆, preferably (CH₂)₂.

12. A process according to any preceding claim in which R 4 is unsubstituted lower alkyl or halogen-substituted lower alkyl.

13. A process according to claim 1 or claim 6 in which R 4 and R together are (CH₂)₂.₆, preferably (CH₂)₂.