US20040053854A1

US20040053854A1 - Process for preparation of 4,5-Epoxymorphinan-6-oxyglucuronides

Info

Publication number: US20040053854A1
Application number: US10/660,474
Authority: US
Inventors: Arie Gutman; Genadi Nisnevitch; Lev Yudovitch; Igor Rokhman
Original assignee: Cenes Ltd
Current assignee: Paion UK Ltd
Priority date: 1998-05-13
Filing date: 2003-09-12
Publication date: 2004-03-18
Also published as: NO20005743D0; EP1077985A1; HUP0102297A3; JP2002514655A; WO1999058545A1; NO20005743L; CA2331866A1; HUP0102297A2; PL344141A1; AU4050499A; US6737518B1; AU761629B2

Abstract

Conjugation of 4,5-Epoxymorphinan-6-ols with Bromoglucuronides in the presence of Zinc containing compounds as activator under conditions capable of forming 4,5-Epoxymorphinan-6-oxyglucuronides is disclosed. This novel approach provides an efficient method for preparation of both anomers of 4,5-Epoxymorphinan-6-oxyglucuronides. The deprotected end products are useful as analgesic agents.

Description

BACKGROUND OF THE INVENTION

According to recent publications the morphine metabolite Morphine-6-β-D-glucuronide (M6G) [6] is a more effective and longer lasting analgesic drug than Morphine [5] with fewer side effects ¹and, therefore, there is much interest in using M6G, rather than Morphine, as a pain killing drug.²

The traditional approach to glycosylation of 4,5-Epoxymorphinan-6-ols explores Bromoolucuronides as glycoside donor and the Koenings-Knorr procedure for the activation of Bromoglucuronides (Berrang, B., et al., Synthesis, 1997, p. 1165 and references cited therein).

Another approach (Scheinmann, F. et. al., U.S. Pat. No. 5,621,087, see claim 1, 2, 5 and 6, abstract, examples, column 4, line 25-line 45) explores the use of Lewis acids (of the type BF ₃and TMSOTf) rather than heavy metals based Lewis acids (March, J., “Advanced Organic Chemistry”, 4-th edition, A Whiley-Interscience publicaiton, pp. 260-3) for the activation of Bromoglucuronides.

Unfortunately, we did not succeed to obtain 4,5-Epoxymorphinan-6-oxyglucuronide from Bromoglucuronides using activators proposed in U.S. Pat. No. 5,621,087 and did not find such examples in the literature.

Unexpectedly we found that the O-clycosylation of 4,5-Epoxymorphinan-6-ols with Bromoglucuronides was accelerated by Zinc containing compounds to give 4,5-Epoxymorphinan-6-oxyglucuronides of formula [1] with high yield.

wherein:

position 7 and 8 can be olefin as shown or dihydro adduct;

R ¹are alkyl, haloalkyl, arylmethyl, acyl, alkoxycarbonyl,

aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl,

R ²is alkyl, haloalkyl or aralkyl;

R ³is alkyl, arylmethyl, allyl, cyclopropylmethyl, cyclobutylmethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl or hydrogen;

R ⁴is alkyl, haloalkyl, arylmethyl, 2-(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl.

We also found that the α and β anomeric selectivity of the conjugation product can be controlled by using different O-protecting groups in aglycon and in Bromoglucuronide as well as by varying the ratio between 4,5-Epoxymorphinan-6-ols and Zinc containing compounds.

It is important to note that only the H-anomer of 4,5-Epoxymorphinan-6-oxyglucuronides was obtained according to Koenings-Knorr procedure and U.S. Pat. No. 5,621,077 procedure (but with another then Bromoglucuronide glycoside donor).

All of the previously disclosed methods have serious drawbacks for producing material to be used as a pharmaceutical drug. A desirable goal, met by the present invention, has been to devise a synthetic procedure without using commercially inaccessible and expensive reagents, and which cleanly produces the desired 4,5-Epoxymorphinan-6-oxyglucuronides, avoiding tedious and expensive purification steps.

SUMMARY OF THE INVENTION

The present invention provides a commercially acceptable process for conjugation of 4,5-Epoxymorphinan-6-ols of formula [3] with Bromoglucuronides of formula [2] in the presence of Zinc containing compounds under conditions capable of forming 4,5-Epoxymorphinan-6-oxyglucuronides [1].

wherein

position 7 and 8 can be olefin as shown or dihydro adduct;

R ¹, R², R³, and R⁴, are as defined above.

This novel approach was used for the preparation of the known analgesic agent Morphine-6-β-glucuronide [4] and of its α-anomer.

Other features and advantages will be apparent from the specification and claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to a novel process for conjugation of 4,5-Epoxymorphinan-6-ols with Bromoglucuronides.

Particularly, the present invention relates to the use of Zinc containing compounds for the activation of Bromoglucuronides in the O-glycosylation reaction of 4,5-Epoxymorphinan-6-ols.

This novel approach has the following advantages:

Zinc containing compounds as activating reagents of Bromoglucuronides are inexpensive and commercially available.

Use of different O-protecting groups in the aglycon and in the Bromoglucuronide as well as different ratio of 4,5-Epoxymorphinan-6-ols and Zinc containing compounds enable to obtain high anomeric selectivity and produce at will with a high degree of preference either the α or the β anomer.

Although any 4,5-Epoxymorphinan-6-ols are suitable for this O-glycosylation, preferably, compounds of formula [3] are used

wherein

position 7 and 8 can be olefin as shown or dihydro adduct; R ³and R⁴are as previously defined.

More preferably, said 4,5-Epoxymorphinan-6-ols are selected from 3-O-Acylmorphine, 3-O-Acylnormorphine, 3-O-Acylnalbuphine, 3-O-Acylnalorphine, 3-O-Acyldihydromorphine, 3-O-Benzylmorphine, 3-O-Benzyldihydromorphine, N,O ³-Dibenzylnornorphine, Codeine, Ethylmorphine, Dihydrocodeine, Pholcodine, 3-O-Alkoxycarbonylmorphine, 3-O-Benzyloxycarbonylmorphine, N,O³-Bis(benzyloxycarbonyl)normoiphine.

Although any Bromoglucuronide may be used, it is preferred that compounds of formula [2] are used.

wherein

R ¹and R²are as previously defined.

More preferably the Bromoglucuronides of the present invention are selected from the compounds of formula [2a].

wherein

R are acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl,

vinyloxycarbonyl, allyloxycarbonyl;

R ²is as previously defined.

Most preferably Bromoglucuronides of formula [2b] are used.

wherein

R are as previously defined.

Although any Zinc containing compound suitable as activating reagents for this O-glycosylation can be used, preferably, Zinc Bromide is used.

It is preferred that about 0.01 equivalents to about 4 equivalents and especially preferred that about 0.5 equivalents to about 2 equivalents of Zinc containing compound is used.

Preferably about 1 equivalent to about 2 equivalents of the Bromoglucuronide [2] is used. It is specially preferred that about 1 equivalent to about 1.5 equivalents of Bromoglucuronide [2] is used. The said 4,5-Epoxymorphinan-6-ol [31] may be used as an individual compound or alternatively as corresponding salts thereof or complexes. Especially preferred is the use of said Zinc containing salt or complexes of [3] without using additional Zinc containing compounds as promoter for said coupling. It is preferred that the said complexes may be prepared in situ.

It may be also preferred to conduct the said Zinc activated O-glycosylation in the presence of additives to buffer or to promote the said Zinc containing compounds. The above additives may be selected from molecular sieves, tertiary amines, tetraalkylureas, organic and inorganic acids and salts.

Any reaction-inert solvent may be used. As used above and elsewhere herein, the expression “reaction-inert solvent” refers to a solvent which does not react or decompose with starting materials, reagents, intermediates or products in a manner which adversely affects the yield of the desired product. In general, the solvent can comprise a single entity, or contain multiple components. Preferably the sovent is a non-protic reaction inert solvent and it is especially preferred that the solvent is Dichloromethane because of the exellent stereoselectivity it provides. Another solvent may be Chloroform or Dichloroethane.

Any environment or conditions (e.g. temperature, time, solvent) suitable for (i.e., capable of) forming the desired 4,5-Epoxymorphinane-6-oxyglucuronides may be used. However, it is preferred that the reaction occurs at a temperature of about −20° C. to about 100° C. and preferably from about 40° C. to 65° C. Below about −20° C. the reaction can be slow and above about 100° C. undesired side reactions (e.g. anomerisation) can occur. This reaction is conveniently carried out at about 0.5 to about 3 atmospheres, however, the high pressures are espesially preferred for the said coupling.

The present invention could be used as a general method to produce a large number of new compounds. As a result of the said coupling also the salts and complexes of 4,5-epoxymorphinan-6-oxyglucuronides [1] could be obtained in a convenient way.

This invention makes a significant advance in the field of 4,5-Epoxymorphinan-6-oxyglucosides by providing efficient methods of preparing both anomers of 4,5-Epoxymorphinan-6-oxyglucuronides. The deprotected end products are usefuil as analgesic agents.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit and scope of this novel concept as defined by the following claims.

EXAMPLES

Example 1

Preparation of Codeine-β-glucuronide [4a]

[0051]
1.1 Preparation of Methyl (3-O-methylmorphin-6-yl-2′,3′,4′-tri-O-acetyl-β-D-glucopyranosid)uronate [1e][0052]
A mixture of Methyl acetobromo-α-D-glucuronate [2c] (0.20 g), Codeine [3b] (0.10 g), 3 Å Molecular Sieves (0.3 g) and Dichloromethane (10 mL) was stirred at room temperature for 5 hours. Anhydrous Zinc Bromide (0.08 g) was added in one portion and the resulting mixture was refluxed for 48 hours. Dichloromethane (20 mL) and Sodium Hydrogencarbonate saturated aqueous solution (10 mL) were added to the cooled reaction mixture. After stirring for 30 min the organic layer was separated and washed with Sodium Hydrogencarbonate saturated aqueous solution and Water. The aqueous layers were combined and washed with Dichloromethane (20 mL) The combined organic layers were dried over anhydrous Sodium Sulfate, filtered and evaporated under reduced pressure. After purification of the residue the desired product was obtained in the yield of 58% (0.12 g). Its structure was confirmed by [0053] ¹H NMR (CDCl)₃
1.2 Hydrolysis of compound [1e]. [0054]
Hydrolysis of compound [1e] was carried out according to the known procedure (Carrupt, P.-A. et al., J. Med. Chem., 1991, v. 34, 1272). Codeine-β-glucuronide was obtained with 50% yield. Its structure was confirmed by [0055] ¹H NMR (D2O), ¹³C NMR, HR-MS.

EXAMPLE 2

Preparation of Morphine-6-β-glucuronide [M6G] [4].

[0056]
2.1 Preparation of Methyl (3-O-methoxycarbonylmorphin-6-yl-2′, 3′,4′-tri-O-acetyl-β-D-glucopyranosid)uronate [1f][0057]
A mixture of Methyl acetobromo-α-D-glucuronate [2c], (39.7 g, 100 mmol), 3-O-Methoxycarbonylmorphine [3c] (22.8 g,66.5 mmol) 3 Å Molecular Sieves (50.0 g) and Chloroform (300 mL) was stirred at room temperature for 1 hour. Anhydrous Zinc Bromide (16.1 g, 71.4 mmol) was added in one portion and the resulting mixture was stirred at 50-55° C. for 60 hours under Argon. Sodium Hydrogencarbonate saturated aqueous solution (200 mL) was added to the cooled to room temperature reaction mixture and the stirring was continued for additional 30 min. The organic layer was separated, washed with water, dried over anhydrous Sodium Sulfate, filtered through a short Silica gel column and evaporated under reduced pressure to give 35.0 g (80%) of the crude product. After recrystallisation from iso-Propanol 20.3 g (46.4% yield) of Methyl (3-O-methoxycarbonylmorphin-6-yl-2′, 3′,4′-tri-O-acetyl-β-D-glucopyranosid)uronate [1f] was obtained. Its structure was confirmed by [0058] ¹H NMR (CDCl₃).
2.2. Hydrolysis of compound [1f][0059]
Hydrolysis of compound [1f] was carried out according to known procedure (Carrupt, P.-A. et al., J. Med. Chem., 1991, v. 34, 1272) and gave M6G [4] with 56% yield. Its structure was confirmed by [0060] ¹H NMR (D2O), ¹³C NMR.

EXAMPLE 3

Preparation of Morphine-6-α-glucuronide [4b].

[0061]
3.1 Preparation of Methyl (3-O-acetylmorphin-6-yl-2′,3′,4′-tri-O-acetyl-α/β-D-glucopyranosid) uronate [1g][0062]
A mixture of Methyl acetobromo-α-D-glucuronate [2c] (6.0 g, 15 mmol), 3-O-Acetylmorphine [3c] (3.23 g, 10 mmol) and 3 Å Molecular Sieves (9.0 g) and Dichloromethane (50 mL) was stirred at room temperature for 5 hours. Anhydrous Zinc Bromide (4.50 g, 20 mmol) was added in one portion and the resulting mixture was refluxed for 48 hours. Solution of Sodium hydrogencarbonate (8.0 g) in 80 mL water and Dichloromethane (80 mL) were added to the cold solution. After stirring for 30 min the organic layer was separated and the aqueous layer was washed with Dichloromethane. The combined organic solution was washed with water, dried over anhydrous Sodium Sulfate, filtered and evaporated under reduced pressure. The residue was purified on a short Silica gel column (Dichloromethane →Dichloromethane/Methanol 30:1 v/v) and after concentration under reduced pressure 5.7 g of yellowish powder of the desired Methyl(3-O-acetylmorphin-6-yl-2′,3′,4′-tri-O-acetyl-D-glucopyranosid)uronate [1g] (α/β6:1 mixture according to [0063] ¹H NMR spectra) (91% yield) was obtained.
3.2 Hydrolysis of compound [1g]. [0064]
Sodium Hydroxide (0.40 g, 10.0 mmol) solution in 7.5 mL water was added to a stirred solution of Methyl (3-O-acetylmorphin-6-yl-2′,3′,4′-Tri-O-acetyl-α/β-D-glucopyranosid)uronate (1.6 g, 2.0 mmol) in 30 mL Methanol and the mixture was stirred overnight at room temperature. The solution was then acidified with glacial Acetic acid (5.25 g, 87.3 mmol) to pH 5.5. The solution was cooled to 0° C., Ethanol (20 mL) was added and the obtained mixture was stirred for 1.5 hours. The white precipitate formed under these conditions was filtered off and washed with Ethanol (2 mL). After drying under reduced pressure at 80° C. 0.63 g (62% yield) of Morphine-6-α-glucuronide [4b] was obtained. Its structure was confirmed by [0065] ¹H NMR (D₂O), ¹³C NMR, HR-MS.

EXAMPLE 4-20

Preparation of Compound of Formula [1b]

The syntheses are described by the following Scheme. The procedures set forth in Example 3 were followed with the exceptions apparent from Table 1. Ratio β/α was determined according to [0066] ¹H NMR and/or HPLC.

The procedures set forth in Example 3 were followed with the exceptions apparent from Table 1. Ratio β/α was determined according to ¹H NMR and/or HPLC.

TABLE 1


			ZnBr₂/
Ex. No.	R⁴	R	[3a]	Solv.	β/α

4	Ac	Ac	0.8	CH₂Cl₂	10:1
5	Ac	Ac	0.9	CH₂Cl₂	6:1
6	Ac	Ac	1.0	CH₂Cl₂	2:1
7	Ac	Ac	1.2	CH₂Cl₂	1:2
8	Ac	Ac	1.5	CH₂Cl₂	1:4
9	Ac	Ac	>1.5	CH₂Cl₂	1:6
10	Ac	i-Bu	0.90	CH₂Cl₂	2:1
11	Ac	i-Bu	1.2	CH₂Cl₂	1:1
12	i-Bu	i-Bu	0.85	CH₂Cl₂	3.5:1
13	i-Bu	i-Bu	1.0	CH₂Cl₂	2:1
14	Bz	Ac	1.0	CH₂Cl₂	2:1
15	Bz	i-Bu	0.9	CH₂Cl₂	29:1
16	Bz	i-Bu	1.5	CH₂Cl₂	6:1
17	Bz	Bz	1.0	CH₂Cl₂	10:1
18	MeOCO	Ac	1.0	CHCl₃	6:1
19	MeOCO	Ac	1.4	CH₂Cl₂	5:1
20	Me	Ac	1.1	CH₂Cl₂	>99:1

EXAMPLE 21

Preparation of Methyl (3-O-Acetylmorpbin-6-yl-2′, 3′,4′-Tri-O-acetyl-β-D-glucopyranosid)uronate of formula [8]

[0068]
A suspension of 6.00 g of Methyl Tri-O-acetyl-1-α-bromo-1-deoxy-D-glucopyranuronate of formula [9], 3.23 g of freshly prepared, vacuum-dried 3-O-Acetylmorphine[0069] ⁶and 9.00 g of 3 Å Molecular Sieves in CH₂Cl₂was stirred at room temperature for 5 hours. Anhydrous Zinc Bromide, 2.20 g was added in one portion and the resulting mixture was refluxed for 24 hours. Then an additional 0.30 g of anhydrous Zinc Bromide was added and the mixture was refluxed for additional 24 hours. After this period, the red solution was cooled to room temperature and the mixture of Methylene Chloride (150 mL) and Sodium Hydrogen carbonate saturated aqueous solution (80 mL) was added to the reaction mixture. After stirring for 30 min. the organic layer was separated and washed consequently with Sodium Hydrogen carbonate saturated aqueous solution and Water. The combined aqueous layers were washed with Methylene Chloride. The combined organic layers were dried over Sodium Sulphate anhydrous, filtered and evaporated under reduced pressure. After purification of the residue the desired product was obtained in the yield of 91% (5.7 g).

REFERENCES

1. Osborne, R., et al., Br. J. Clin. Pharm. 1992, v. 34, 130 [0070]
2. Frances, B., et al., J. Pharm. Exp. Ther., 1992, v. 262, 25 [0071]

Claims

1. A process for the synthesis of a protected 4,5-Epoxymorphinan-6-oxyglucuronide of formula [1] or a salt or complex thereof

wherein:

position 7 and 8 are olefin as shown or dihydro adduct;

R¹is alkyl, hialoalkyl, arylmnethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, lialoalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl,

R²is alkyl, haloalkyl or aralkyl;

R³is alkyl, arylmethyl, allyl, cyclopropylmethyl, cyclobutylmethyl, hydrogen, acyl, alkoxycarbonyl, aralkoxycarbonyl, halo alko xycarbonyl , vinyl oxycarbonyl or all yl oxycarbonyl ;

R⁴is alkyl, haloalkyl, arylmethyl, 2(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl.

comprising reaction of a Bromoglucuronide of the formula [2]

wherein

R¹and R²are as previously defined;

with a 4,5-Epoxymoiphinan-6-ols of the formula [3] or a salt or complex thereof

wherein

R³and R⁴are as previously defined;

in the presence of a Zinc containing compound under conditions capable of forming said protected 4,5-Epoxymoiphinan-6-oxyglucuronide [1] or a salt or complex thereof.

2. A process according to claim 1 wherein said 4,5-Epoxymorphinan-6-ol is selected from the compounds of the formula [3a]

wherein

R⁴is as previously defined.

3. A process according to claim 1 wherein said 4,5-Epoxymorphinan-6-ol is selected from 3-O-Acylmorphine, 3-O-Acylnormorphine, 3-O-Acylnalbuphine, 3-O-Acylnalorphine, 3-O-Acyldihydromorphine, 3-O-Benzylmorphine, 3-O-Benzyldihydromorphine, N,O³-Dibenzylnormorphine, Codeine, Ethylmorphine, Dihydrocodeine, Pholcodine, 3-O-Alkoxycarbonylmorphine, 3-O-Benzyloxycarbonylmorphine, N,O³-Bis(benzyl oxycarbonyl)normorphine.

4. A process according to claim 1 wherein said Bromoglucuronide is selected from compounds of formula [2a]

wherein

R is acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl; R²is as previously defined.

5. A process according to claim 1 wherein said Bromoglucuronide is selected from compounds of formula [2b]

wherein

R is as previously defined.

6. A process as recited in claim 1 wherein said protected 4,5-Epoxymorphinan-6-oxyglucuronide is an N-Methyl-4,5-epoxymorphinan-6-oxyglucuronide of formula [1a] or derivative.

wherein:

position 7 and 8 can be olefin as shown or dihydro adduct;

R is acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl, benzyoxylcarbonyl, nitrobenzyloxycarbonyl, methoxybenzylcarbonyl or aroxycarbonyl R2 is alkyl, haloalkyl or aralkyl;

R⁴is alkil, haloalkyl, arylmethyl, 2-(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl.

7. A process as recited in claim 1 wherein R²and R³are methyl.

8. A process according to claim 1 wherein said protected 4,5-epoxymorphinan-6-oxyglucuronide is of formula [1b].

wherein

R and R⁴are as previously defined.

9. A process as recited in claim 1 wherein the said reaction occurs in the presence of molecular sieves.

10. A process as recited in claim 1 wherein the reaction occurs in a non-protic reaction inert solvent.

11. A process as recited in claim 10 wherein the inert solvent is selected from Chloroform, Dichloromethane or Dichloroethane.

12. A process as recited in claim 1 wherein the Zinc containing compound is Zinc Bromide.

13. Use of a Zinc complex of a general formula [3b]

wherein

R³and R⁴are as previously defined;

X is a halogen or a cyano-group;

n 0.5÷2

for preparation of a protected 4,5-Epoxymorphinan-6-oxyglucuronide of a general formula [1] or a salt or complex thereof

wherein

R¹, R², R³and R⁴are as previously defined.

14. A process for the synthesis of a protected 4,5-Epoxymorphinan-6-oxyglucuronide of formula [1] or a salt or complex thereof

wherein:

position 7 and 8 are olefin as shown or dihydro adduct; R¹is alkyl, haloalkyl, arylmethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl;

R²is alkyl, haloalkyl or aralkyl;

R³is alkyl, arylmethyl, allyl, cyclopropylmethyl, cyclobutylmethyl, hydrogen, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl;

R⁴is alkyl, haloalkyl, arylmethyl, 2-(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl

comprising reaction of Bromoglucuronide of the formula [2]

wherein

R¹and R²are as previously defined;

with complex of the formula [3b] under conditions capable of forming said protected 4,5-Epoxymorphinan-6-oxyglucuronide [1] or a salt or complex thereof.

15. A compound having the following formula:

wherein:

position 7 and 8 is olefin as shown or dihydro adduct;

R²and R³are as previously defined;

R⁶is selected from alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl and R⁵is selected from alkyl, haloalkyl, arylmethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl or R⁶is selected from alkyl, haloalkyl, arylmethyl, 2-(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl when one of R⁵is selected from alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl.

16. A compound having the following formula:

wherein:

position 7 and 8 is olefin as shown or dihydro adduct;

R⁷is hydrogen, alkyl, haloalkyl, arylmethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl;

R⁸is hydrogen, alkyl, haloalkyl or aralkyl;

R⁹is hydrogen, alkyl, arylmethyl, allyl, cyclopropylmethyl, cyclobutylmethyl, hydrogen, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl;

R¹⁰is hydrogen, alkyl, haloalkyl, arylmethyl, 2-(4-morpholinyl)ethyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, haloalkoxycarbonyl, vinyloxycarbonyl or allyloxycarbonyl.

17. A compound of formula [1c] according to claim 15 wherein R²and R³are both Me.

18. A protected 4,5-Epoxymorphinan-6-oxyglucuronide synthesised according to any of claims 1 to 12 or 14.

19. A process for synthesising M6G comprising: synthesising a protected 4,5-Epoxymorphinan-6-oxyglucuronide according to any of claims 1 to 12 or 14; and hydrolysing the protected 4,5-Epoxymorphinan-6-oxyglucuronide to form M6G.

20. M6G synthesised according to claim 19.

21. M6G synthesised using a zinc complex according to claim 13.