Field of the invention

This invention is in the field of novel moφhine-6-glucuronate and codeine-6-glucuronate analogues and their use in therapy as opioid analgesic agents.

Background to the invention

Description QΪ the prior art

While opium has been used for centuries to control pain, it was only in the mid- 1920's that the structure of the principle active alkaloid, morphine was established. The opioid analgesic morphine is often the drug of choice for terminally ill cancer patients and in other cases of severe pain. Although traditionally used by the intramuscular route, other routes of administration, particularly the oral administration of morphine is becoming more widespread. One of the drawbacks however to the use of orally administered morphine is a variable absoφtion and metabolism of the moφhine by individual patients due to extensive hepatic metabolism and poor bio-availability which results in an unpredictive effectiveness. Additionally, it is well known that the therapeutic use of moφhine gives rise to various side effects such as respiratory depression, nausea, vomiting, abuse potential etc.

Despite these disadvantages, moφhine is still often the analgesic of choice and its use is generally increasing.

It has been reported that metabolites of moφhine such as moφhine-6-glucuronide (M6G) may be as or more active than the parent drug with less chance of side effects. Osborne si a].(1988), The Lancet, April 6, p 828 has discussed the use of moφhine-6- glucuronide as a drug substance in its own right. In animals, moφhine-6-glucuronide is a more potent antinociceptive agent than moφhine, the exact relationship depending on the test model and route of administration, but always being more potent when administered by the intrathecal route. Nevertheless, the physicochemical characteristics of moφhine-6-glucuronide restricts any potential oral administration and hence reduces its clinical usefulness. It is thus desirable to identify

other derivatives of moφhine which preserve the pharmokinetic advantages of moφhine-6- glucuronide but with improved oral bioavailability for their properties as analgesic agents. Summary of the invention

The inventors have identified and synthesised 6-substituted derivatives of moφhine and codeine, another opioid analgesic compound.

Accordingly the invention provides a compound of Formula I below

wherein R\ = H (moφhine analogue), CH3 (codeine analogue)

R > = H, alkyl group of 1 to 4 carbon atoms, allyl, cyclopropylmethyl

O I

R3 = a group -O-C-R4 -O-CH2-R4 (ether)

-O-COCH = CHR4 (cinnamate)

wherein R4

wherein X\, X2, X3, X4 and X5 which may be the same or different are separately selected from H, an alkyl group of 1 to 4 carbon atoms, NH2, NO2, alkoxy group of 1 to 4 carbon atoms, hydroxy, halogen, N-alkyl group of 1 to 4 carbon atoms, moφholine, a group COR5 wherein R5 is H, OH, O-alkyl where alkyl is from 1 to 4 carbon atoms, or one of Xj and X , X2 and X3, X3 and X4 or X4 and X5 together with an alkylene group optionally interrupted by O, S or N of up to 5 atoms in length complete a ring and a pharmaceutically acceptable salt thereof for use in therapy. Description of the preferred embodiments

Moφhine and other traditional opiate analgesics act through opioid μ receptors to induce analgesia together with the well known side effects of addiction, respiratory depression etc., whilst opioid K receptors may mediate psychomimetic and other effects. It is known that the opioid receptor profile of moφhine and moφhine-6-glucuronide differ. The compounds of the present invention exaggerate this difference resulting in compounds which have an equivalent μ-affinity, a higher 6 -affinity and a lower K-affinity. Hence the compounds of the invention are more beneficial than M6G, by being as well as more bio- available, having reduced κ-mediated side effects.

Of all the compounds in the above Formula I the preferred moφhine (R _j = H) and codeine (R\ = CH3) derivatives are those wherein R2 is H, an alkyl group of 1 to 4 carbon atoms, preferably methyl or allyl (thus forming naloφhine-type derivatives). R3 is preferably a grouping

O I

-O-C-R4 and R4 is preferably a group

wherein Xi , X ₂ , X3, X4 and X ₅ are H, NH ₂ , NO ₂ , OH, halogen or COR5 where R ₅ is

OH. In all cases, when the compound of the invention contains an alkyl group, this may be linear or branched.

In the above compounds preferably at least 3 of X , X2, X3, X4 and X5 are H. Where there are substituents, the substituents may be in the ortho, meta or para positions but where there is only one substituent preferably this is in the ortho position, more preferably in the para position and where there is more than one substituent, one is in the para position. Where there is an alkylene ring formed by two of X\, X2, X3, X4 and X5, preferably this is between X2 and X3 or X3 and X4. It may be, for example a group -O-CH ₂ -O. Of all the compounds embraced by Formula I, the preferred compounds are moφhine or codeine-6-nitrobenzoate, moφhine or codeine-6-hydroxybenzoate and moφhine or codeine-6-phthalate.

As stated above, the moφhine-6-glucuronide analogues and codeine-6-glucuronide analogues are believed to function as analgesic agents. Thus, the invention further provides a pharmaceutical composition which comprises a compound of Formula I together with a pharmaceutically-acceptable diluent or carrier, preferably one which is sterile and pyrogen free. As indicated, the compounds may be formulated as salts formed with physiologically acceptable inorganic or organic acids and when so formulated it is preferred to use methane sulphonic acid, isethionic acid, tartaric acid or another solubilising acid. The compounds of Formula I may be formulated singly or as a mixture of two or more compounds for use as pharmaceuticals by a variety of methods. The composition may be in a form suitable for oral administration as a tablet or capsule or liquid medicine, a suppository or in a form suitable for parenteral administration by for example injection or infusion, as a sterile solution or infusion. The compounds may be formulated for controlled delayed release, e.g. in tablets and suppositories.

Pharmaceutical compositions containing compounds of Formula I may be formulated in unit dosage form, i.e. in the form of discrete portions, each containing a unit dose or a multiple or sub-multiple of a unit dose.

Without limitations to dosages it may be stated that the compound of Formula I will normally be administered to a warm-blooded animal at a dose within the range for example in man of 1-100 mg orally more preferably 5-50 mg orally or by intramuscular or

subcutaneous injection up to 6 times daily. As a general guide, the dosage used will be equivalent to or slightly less than dosages of moφhine or codeine which are well characterised and known to a person skilled in the art. It will be appreciated however that the specific dosage for a patient will depend on how much pain that patient is experiencing and actual dosages in this case will be determined by the attending medical staff.

It is believed that most of these compounds are novel, thus, according to a further aspect of the invention there is provided a compound of Formula II.

wherein

R _j = H (moφhine analogue), CH3 (codeine analogue)

R2 = H, alkyl group of 1 to 4 carbon atoms, allyl, cyclopropylmethyl

O I R ₃ = a group -O-C-R4

-O-CH2-R4 (ether)

-O-COCH = CHR4 (cinnamate)

wherein R4 =

X ₅ X,

wherein Xγ, X2, X3, X4 and X5 which may be the same or different are separately selected

from H, an alkyl group of 1 to 4 carbon atoms, NH2, NO2, alkoxy group of 1 to 4 carbon atoms, hydroxy, halogen, N-alkyl group of 1 to 4 carbon atoms, moφholine, a group COR5 wherein R5 is H, OH, O-alkyl where alkyl is from 1 to 4 carbon atoms, or one of X\ and X2, X2 and X3, X3 and X4 or X4 and X5 together with an alkylene group optionally interrupted by O, S or N of up to 5 atoms in length complete a ring with the proviso that not all Xi, X2, X3, X4 and X5 are hydrogen and pharmaceutically acceptable salts thereof.

The novel moφhine-6-glucuronide analogues and codeine-6-glucuronide analogues of the invention may be prepared by any process known to be applicable to the preparation of chemically related compounds. Accordingly, such processes form a further feature of the invention.

In particular, the codeine-6-benzoate derivatives for example may be synthesised from codeine by reaction with the appropriate acid anhydride or acid chloride in the presence of dimethylammino pyridine (DMAP). Protection of the 3-hydroxy functions of moφhine as the 3-t-butyldimethylsilyl (3-t-BDMS) ether allows synthesis of the corresponding moφhine analogues after deprotection of the 3-t-BDMS-6-esters with tetrabutylammonium fluoride (TBAF).

As a further example moφhine and codeine-6-ethers may be prepared by the reaction of codeine or similarly protected moφhine with the appropriate alkyl chloride in the presence of sodium hydride in THF.

According to a further aspect of the invention there is provided a method of alleviating pain in an individual in need of such treatment which comprises administering to said individual a therapeutically effective amount of a compound of Formula I or II as defined hereinbefore. The invention also provides the use of a compound of Formula I or II as defined hereinbefore in the manufacture of a novel medicament for use in alleviating pain.

The invention is illustrated by the following Examples in which Figure 1 referred to illustrates pathways for the synthesis of codeine analogues; Figure 2 referred to illustrates pathways for the synthesis of moφhine analogues.

EXAMPLE 1: SYNTHESIS OF CODEINE ANALOGUES OF MfiP.

The syntheses of the compounds described in this Example are shown schematically in Figure 1.

Preparation of 7,8-Didehydro-4,5a-epoxy-3-methoxy-l 7-methyl-6a- succinyloxy-morphinan (1)

A mixture of codeine (1 g, 3.34 mmol) and succinic anhydride (2g, 20 mmol) in pyridine (5 cm ³ ) was refluxed for 1 hr. The hot reaction mixture was poured onto ice and the resulting white precipitate collected on a filter. The precipitate was washed with cold water. Crystallisation from DCM-petroleum ether gave the ester (1) (240 mg, 18%) m.p. 154-6°C; acid); δ _H (CDCl ³ ) 1.89 (1 H, d, J 13.5, 15e-H), 2.39-2.79 (11 H, m, NMe, 16-H ₂ , 19-H ₂ , 20-H ₂ , lOo and 15a-H), 3.01 (1 H, d, J 19, lOβ-H), 3.11 (1 H, t, J 2.5, 14-H), 3.76 (1 H, q, J 3, 9-H), 3.86 (3 H, s, OMe), 5.15 (1 H, d, J 6.5, 5-H), 5.28 (2 H, m, 6 and 8-H), 5.60 (1 H, d, J 10, 7-H), 6.55 and 6.68 (2 H, ABq, 1 and 2-H); m/z 399 (M ⁺ 13%) 299(100), 282(22), 229(29), 188(14), 162(31), 124(27), 70(17), 56(56), 42(49).

Preparation of 6a-(2-Carboxyben2 loxy)-7,8-didehydro-4,5a-epoxy-3-methoxy- 17-methyl-morphinan (2) A mixture of codeine (1 g, 3.34 mmol) and phthalic anhydride (2 g, 13.5 mmol) in pyridine (5 cm ³ ) was refluxed for 1 hour. The hot reaction mixture was poured onto ice and the resulting white precipitate collected on a filter. The precipitate was washed with cold water Crystallisation from DCM-petroleum ether gave the ester (2) (2.67 g, 88%) m.p. 227-8 ^e C (decomp); max nujoiycπf ¹ 3417 (OH), 1713 (C=O ester), 1608 (C=O acid); δ _H (CDCl ₃ ) 1.98 (1 H, d, J 13.5, 15e-H), 2.68-2.97 (7 H, m, NMe, lOo, 15a, 16-H and OH), 3.07 (1 H, d, J 19, lOβ-H), 3.44 (1 H, d, J 7, 16-H), 3.59 (1 H, t, J 2.5, 14-H), 3.85 (4 H, m, OMe and 9-H), 5.44 (3 H, m, 5, 6 and 8-H), 5.80 (1 H, d, J 8.5, 7-H), 6.61 and 6.74 (2 H, ABq, 1 and 2-H), 7.37 (1 H, t, J 7.5, 21-H), 7.51 (1 H, t, J 7.5, 22-H), 7.67 (1 H, d, J 7.5, 20-H), 8.04 (1H, d, J 7.5, 23-H); δ _C 21.40, 32.09, 36.84, 40.80 (NMe), 40.96, 47.31,

56.99 (OMe), 60.11, 67.66, 87.38, 115.40, 119.88, 122.83, 126.79, 127.29, 127.90, 129.75,

129.98, 130.22. 131.16, 131.39, 132.07, 143.26, 146.81, 166.68, 175.83; m/z 447 (M ⁺ ) 299(100), 282(10), 229(14), 148(7), 124(11), 104(33), 76(19). [FAB-MS. Found (M+H ⁺ ): 448.1752. C ₂ 6H ₂ 6NO ₆ requires 448.1760].

Preparation of 6a-Benzoyloxy-7,8-didehydro-4,5a-epoxy-3-methoxy- 17-methyl-morphinan (3)

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen, was added benzoyl chloride (0.35 ml, 1 mmol) and the reaction stirred at room temperature for 4 hours. DCM (10 ml) was added and the solution washed with a 5% CUSO4 solution and water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in DCM) to give the ester (3) (295 mg, 73%).

Alternatively a mixture of codeine (300 mg, 1 mmol), benzoic acid (122 mg, 1 mmol) and DMAP (122 mg, 1 mmol) in DCM was stirred for 1 hour at 0°C, the flask being fitted with a calcium chloride guard tube. DCC (230 mg, 1.1 mmol) was added and the solution, which was stirred at 0°C for 5 min before being allowed to warm up to room temperature, followed by stirring for a further 3 hours. The reaction mixture was washed successively with dilute HCl/water/bicarbonate/water, dried (MgSO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in DCM) to give the ester (3) (275 mg, 68%).

Recrystallisation in each case from DCM-petroleum ether gave crystals m.p. 130-132°C; 1717 (C=O ester); δ _H (CDCl ₃ ) 1.91 (1 H, d, J 12.5,

15e-H), 2.12 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.37 (2 H, m, 10α and 16-H), 2.48 (3 H, s,

NMe), 2.65 (1 H, dd, J 12.5, 4, 16-H), 2.86 (1 H, t, J 2.5, 14-H), 3.06 (1 H, d, J 18.5, lOβ-H), 3.42 (1 H, q, J 3, 9-H), 3.72 (3 H, s, OMe), 5.20 (1 H, d, J 6.5, 5-H), 5.47 (2 H, m,

6 and 8-H), 5.78 (1 H, d, J 10, 7-H), 6.55 and 6.67 (2 H, ABq, 1 and 2-H), 7.43 (2 H, t, J 8, 21 and 23-H), 7.55 (1 H, t, J 8, 22-H), 8.09 (2 H, d, J 8, 20 and 24-H); δ _c 21.36, 35.09, 40.39, 42.50, 42.85 (NMe), 46.63, 56.79 (OMe), 59.08, 68.40, 87.95, 114.59, 119.13, 126.66, 128.13, 128.57, 129.31, 129.80, 130.63, 132.91, 142.10, 146.70, 165.92; m/z 403 (M ⁺ , 53%) 282(28), 266(23), 229(14), 155(15), 122(31), 105(100), 77(51). (Found M ⁺ , 403.1795. C25H25NO4 requires 403.1783).

Preparation of 7,8-Didehydro-4,5a-epoxy-6a-(4-fluorobenzoyloxy)-3- raethoxy-17-methyl-morphinan (4 X=F in Figure 1)

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-fluorobenzoyl chloride (0.35 cm ³ , 477 mg, 3 mmol) and the reaction stirred at room temperature for 10 minutes. CHCI3 was added and the solution washed successively with dilute HCl/water/bicarbonate/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in CHCI3) to give the ester (4 X=F in Figure 1) (403 mg, 95%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 136-39°C; v _maχ (nujol)/cm"^ 1717 (C=O ester); δ _H (CDCl ₃ ) 1.92 (1H, d, J 12.5, 15e-H), 2.16 (1 H, dt, J 12.5, 5, 5,

15a-H), 2.42 (2 H, m, lOo and 16-H), 2.52 (3H, s, NMe), 2.75 (1 H, dd, J 12.5, 4, 16-H), 2.92 (1 H, t, J 2.5, 14-H), 3.08 (1 H, d, J 18.5, lOβ-H), 3.53 (1 H, q, J 3, 9-H), 3.72 (3 H, s, OMe), 5.20 (1 H, d, J 6.5, 5-H), 5.43 (1 H, m, 6-H), 5.51 (1 H, d, J 10, 8-H), 5.77 (1 H, d, J 10, 7-H), 6.58 and 6.68 (2 H, ABq, 1 and 2-H), 7.1 1 (2 H, m, 21 and 23-H), 8.10 (2 H, m, 20 and 24-H); δ _C 20.63, 34.82, 39.98, 42.41, 42.60 (NMe), 46.60, 56.74 (OMe), 59.04,

68.41, 87.85, 1 14.49, 1 15.24, 115.59, 119.37, 126.36, 128.69, 129.26, 130.49, 132.43, 132.58, 142.30, 146.76, 165.05, 167.88; m/z 421 (M\ 53%) 282(28), 266(23), 229(14), 155(15), 122(31), 105(100), 77(51). (Found M ⁺ , 421.1689. C25H24NFO4 requires 421.1725).

Preparation of 6a-(4-Chlorobenzoyloxy)-7,8-didehydro-4,5a-epoxy- 3-methoxy-17-methyl-morphinan (5 X=C1 in Figure 1)

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-chlorobenzoyl chloride (0.38 ml, 527 mg, 3 mmol). The reaction mixture was stirred at room temperature for 10 min. EtOAc was added and the solution washed successively with dilute HCl/water bicarbonate/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 10% MeOH in CHCI3) to give the ester (5 X=C1 in Figure 1) (315 mg, 72%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 165-67°C; v _maχ (CHCI3) cm" ¹ 1719 (C=O ester); δ _H (CDCl ₃ ) 1.91 (1 H, d, J 12.5, 15e-H),

2.1 1 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.38 (2 H, m, lOo and 16-H), 2.49 (3 H, s, NMe),

2.65 (1 H, dd, J 12.5, 4, 16-H), 2.87 (1 H, t, J 2.5, 14-H), 3.07 (1 H, d, J 18.5, lOpH), 3.46 (1 H, q, J 3. 9-H), 3.72 (3 H, s, OMe), 5.19 (1 H, d, J 6.5, 5-H), 5.43 (1 H, m, 6-H), 5.50 (1 H, d, J 10.8-H), 5.76 (1 H, d, J 10, 7-H), 6.57 and 6.67 (2 H, ABq, 1 and 2-H), 7.41 (2 H, d, J 8, 21 and 23-H), 8.02 (2 H, d, J 8, 20 and 24-H); δ _c 20.63, 35.30, 40.59, 42.62, 43.01, (NMe), 46.70, 56.74 (OMe), 59.12, 68.68, 87.93, 114.35, 119.31, 126.95, 128.49, 128.60, 128.81, 129.75, 130.73, 131.33, 139.47, 142.18, 146.18, 146.52, 165.20; m/z 439 and 437 (M ⁺ , 23 and 63%) 302(8), 300(24), 282(58), 229(26), 155(12), 141(33), 139(100), 111(38), 94(9), 59(44), 42(54). (Found M\ 439.1364 and 437.1394. C25H24NCIO4 requires 439.1383 and 437.1397).

Preparation of 6a-(4-Bromobenzoyloxy)-7,8-didehydro-4,5a-epoxy-3- methoxy-17-methyl-morphinan (6 X=Br in Figure 1)

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-bromobenzoyl chloride (1.1 g, 5 mmol) and a catalytic amount of DMAP. The reaction mixture was stirred at room temperature for 10 minutes. CHCI3 was added and the solution washed successively with dilute HCl/water/bicarbonate/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in CHCI3) to give the ester (6 X=Br in Figure 1) (441 mg, 92%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 177-80°C; v _max (CHCl ₃ )/cm- ¹ 1719 (C=O ester); δ _H (CDCl ₃ ) 1.90 (1H, d, J 12.5, 15e-H), 2.11 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.37 (2 H, m, lOo and 16-H), 2.48 (3 H, s, NMe), 2.65 (1 H, dd, J 12.5, 4, 16-H), 2.85 (1 H, t, J 2.5, 14-H), 3.07 (1 H, d, J 18.5, lOβ-H), 3.44 (1 H, q, J 3, 9-H), 3.72 (3 H, s, OMe), 5.19 (1 H, d, J 6.5, 5-H), 5.42 (1 H, m, 6-H), 5.51 (1 H, d, J 10, 8-H), 5.76 (1 H, d, J 10, 7-H), 6.57 and 6.67 (2 H, ABq, 1 and 2-H), 7.58 (2 H, d, J 8, 21 and 23-H), 7.94 (2 H, d, J 8, 20 and 24-H); δ _c 20.46, 35.14,

40.38, 42.54, 42.88 (NMe), 46.68, 56.74 (OMe), 59.10, 68.62, 87.84, 114.38, 119.34, 126.72, 128.16, 128.42, 128.92, 129.60, 130.63, 131.46, 131.60, 142.23, 146.66, 165.31 ; m/z 483 and 481 (M ⁺ , 80 and 90%), 282(100), 346 and 344(25 and 27), 229(42), 185 and 183(76 and 83), 157(27), 105(34), 81(38), 59(52). (Found M\ 483.0887 and 481.0716. C ₂ 5H ₂ 4NBrO ₄ requires 483.0869 and 481.0889).

Preparation of 7,8-Didehydro-4,5a-epoxy-3-methoxy-17-methyl-6a- (4-nitrobenzoyloxy)-morphinan (7 X=NO|2 in Figure 1 )

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen was added p-nitrobenzoyl chloride (560 mg, 3 mmol) and the reaction stirred at room temperature for 4 hours. EtOAc was added and the solution washed with 5% CUSO4 solution/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 15% MeOH in CHCI3) and TLC plates (run in CHCl ₃ /MeOH/NH OH) to give the ester (7 X=NO ₂ in Figure 1) (283 mg, 63%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 186-87°C; 1722 (C=O ester); δ _H (CDCl ₃ ) 1.90 (1 H, d, J 12.5, 15e-H), 2.08 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.34 (2 H, m, 10a and 16-H), 2.46 (3 H, s, NMe), 2.61 (1 H, dd, J 12, 4, 16-H), 2.83 (1 H, t, J 2.5, 14-H), 3.07 (1 H, d, J 18.5, 10p-H), 3.40 (1 H, q, J 3, 9-H), 3.71 (3 H, s, OMe), 5.20 (1 H, d, J 6.5, 5-H), 5.47 (1 H, m, 6-H), 5.55 (1 H, d, J 10, 8-H), 5.76 (1 H, d, J 10, 7-H), 6.58 and 6.67 (2 H, ABq, 1 and 2-H), 8.27 (4 H, m, 20, 21, 23 and 24-H); δ 20.30, 35.35, 40.66, 42.59, 43.09, (NMe), 46.74, 56.49 (OMe), 59.13, 69.17, 87.57, 113.86, 119.46, 123.40, 127.03, 127.80, 130.20, 130.60, 131.07, 142.18, 146.44, 150.59, 164.22; m z 448 (M ⁺ , 84%), 311(20), 282(82), 229(25), 152(16), 104(44), 92(20), 76(42), 59(39), 50(100), 44(58). (Found M\ 448.1607C ₂ 5H ₂ 4N ₂ O ₆ requires 448.1634).

Preparation of 7,8-Didehydro-4,5a-epoxy-3-methoxy-6a-(4-methoxybenzoyloxy)- 17-methyl-morphinan (8 X=OMe in Figure 1)

To a solution of codeine (300 mg, 1 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-anisoyl chloride (0.45 ml, 513 mg, 3 mmol) and the reaction stirred at room temperature for 10 minutes. EtOAc was added and the solution washed successively with dilute HCl/water/bicarbonate/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in DCM) to give the ester (8 X=OMe in Figure 1) (426 mg, 98%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 174-76°C; v _max (CUC\τ ₎ )lcm- ¹ 171 1 (C=O ester); δ _H (CDCl ₃ ) 1.90 (1 H, d, J 12.5, 15e-H), 2.09 (1 H, dt, J 12, 5, 5, 15a-H), 2.36 (2

H, m, lOo and 16-H), 2.48 (3 H, s, NMe), 2.62 (1 H, dd, J 12, 4, 16-H), 2.83 (1 H, t, J 2.5,

14-H), 3.06 (1 H, d, J 18.5, lOβ-H), 3.42 (1 H, q, J 3, 9-H), 3.44 (3 H, s, OMe), 3.74 (3 H, s, OMe), 5.18 (1 H, d, J 6.5, 5-H), 5.41 (1 H, m, 6-H), 5.48 (1 H, d, J 10, 8-H), 5.76 (1 H, d, J 10, 7-H), 6.55 and 6.66 (2 H, ABq, 1 and 2-H), 6.92 (2 H, d, J 9, 21 and 23-H), 8.04 (2 H, d, J 9, 20 and 24-H), δ _c 20.49, 35.28, 40.54. 42.69, 42.94 (NMe), 46.63, 55.42 (OMe), 57.02 (OMe), 59.05, 68.34, 88.32, 114.82, 119.19, 122.41, 126.97, 128.85, 129.42, 130.90, 131.98, 142.16, 146.78, 163.47, 165.77; m z 433 (M ⁺ , 43%), 282(20), 229(12), 152(14), 135(100), 77(16), 44(11). (Found M ⁺ , 433.1915 C ₂ 6H 7NO ₅ requires 433.1889).

Preparation of 7,8-Didehydro-4,5a-epoxy-3-methoxy-6a-(3,4- methylenedioxy benzoyloxy)-l 7-methy 1-morphinan (9)

To a solution of codeine (200 mg, 0.67 mmol) in DCM (2 cm ³ ) at 0°C, under nitrogen, was added piperonylic acid (333 mg, 2 mmol) and DMAP (82 mg, 0.67 mmol) and the solution was stirred for 30 min. DCC (152 mg, 0.74 mmol) was added and the reaction flask fitted with a calcium chloride guard tube. After stirring for 5 minutes at 0°C, the reaction mixture was allowed to warm up to room temperature and stirred overnight. The reaction mixture was filtered, washed with water/bicarbonate, dried (MgSO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 10% MeOH in CHCI3 ) to give the ester (9) (195 mg, 65%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 63-5°C; ^v maχ( ^CHC1 3) ^{cm"1 17U} ( ^{C=0 ester} )' δ _H (CDCl ₃ ) ⁹ ° 0 ^H > ^d ' ^{J 12} - ⁵ < 15e-H), 2.1 1 (1 H, dt, J 12, 5, 5, 15a-H), 2.37 (2 H, m, lOo and 16-H), 2.46 (3 H, s, NMe), 2.64 (1 H, dd, J 12, 4, 16-H), 2.84 (1 H, t, J 2.5, 14-H), 3.06 (1 H, d, J 18.5, lOp-H), 3.44 (1 H, q, J 3, 9-H), 3.76 (3 H, s, OMe), 5.17 (1 H, d, J 6.5, 5-H), 5.41 (1 H, m, 6-H), 5.50 (1 H, d, J 10,8-H), 5.75 (1 H, d, J 10, 7-H), 6.03, (1 H, s, CH,), 6.56 and 6.67 (2 H,

ABq, 1 and 2-H), 6.84 (1 H, d, J 8, 23-H), 7.52 (1 H, d, J 1.5, 20-H), 7.70 (1 H, dd, J 8, 1.5, 24-H); m z 447 (M ⁺ , 40%) 310(17), 282(25), 229(13), 165(29), 149(100), 121(20), 91(8), 65(25), 42(21). (Found M ⁺ , 447.1679. C26H25NO.5 requires 447.1682).

Preparation of 6a-(4-t-Butyldimethylsilyloxybenzoyloxy)-7,8-didehydro-4,5a- epoxy- 3-methoxy-17-methyl-morphinan (10)

Freshly prepared p-t-BDMS-oxy benzoic acid (500 mg, 1.98 mmol) in DCM (5 cm ³ ),under nitrogen, was treated with oxalyl chloride (630 mg, 0.43 cm ³ , 5 mmol). Effervescence implied formation of the acid chloride. On completion of the reaction, after 20 minutes, benzene (5 cm ³ ) was added and all solvents removed under reduced pressure. To the acid chloride residue, under nitrogen, was added a solution of codeine (200 mg, 0.67 mmol) in pyridine (3 cm ³ ) and the reaction stirred at room temperature for 2 hours. EtOAc was added and the solution washed with dilute HCl/water/bicarbonate/water, dried (MgSO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in DCM) to give the ester (10) (293 mg, 82%). Recrystallisation from DCM-petroleum ether gave crystals m.p. 102-5°C; 1709 (C=O ester); δ _H (CDCl ₃ ) 0.22 (6 H, s, SiMe ₂ ), 0.98 (9 H, s, SiCMe ₃ ), 1.93 (1 H, d. J 12.5, 15e-H), 2.21 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.47 (2 H, m, 10α and 16-H), 2.56 (3 H, s, NMe), 2.83 (1 H, dd, J 12, 4, 16-H),

2.99 (1 H, t, J 2.5, 14-H), 3.08 (1 H, d, J 18.5, lOp-H), 3.60 (1 H, q, J 3, 9-H), 3.73 (3 H, s, OMe), 5.20 (1 H, d, J 6, 5-H), 5.41 (1 H, m, 6-H), 5.48 (1 H, d, J 10, 8-H), 5.78 (1 H, d, J 10, 7-H), 6.57 and 6.68 (2 H, ABq, 1 and 2-H), 6.86 (2 H, d, J 8.5, 21 and 23-H), 7.98 (2 H, d, J 8.5, 20 and 24-H); m z 533 (M ⁺ , 77%) 396(25), 282(57), 235(100), 229(25), 195(52), 149( 14), 121 (44), 91(14), 73(59), 59( 18), 42(34).

(Found M\ 533.2579. C ₃₁ H39NO ₅ Si requires 533.2597).

Preparation of 7,8-Didehydro-4,5a-epoxy-6a-(4-hydroxybenzoyloxy)-3-methoxy- 17-methyl-morphinan (11) To a solution of the codeine ester 10 (100 mg, 0.19 mmol) in THF, under nitrogen, at 0°C was added TBAF-1 M solution in THF (1 cm ³ ). After stirring for 5 minutes the reaction was allowed to warm up to room temperature and stirred for a further 2 hours. EtOAc was added and the solution washed several times with water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 10% MeOH in CHCI3) to give the ester (11) (48 mg, 61 %). Recrystallisation from DCM-petroleum ether gave crystals m.p. 132-5°C;

-maxtø iycm ^"1 3563 (OH). 1712 (C=O ester); δ _H (CDCl ₃ ) 1.91 (1 H, d, J 12.5, 15e-H), 2.15 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.41 (2 H, 10a and 16-H), 2.51 (3 H, s, NMe), 2.68 (1 H, m, 16-H), 2.89 (1 H, t, J 2.5, 14-H), 3.06 (1 H, d, J 18.5, 10p-H), 3.47 (1 H, q, J 3, 9-H), 3.73 (3 H, s, Ome), 5.19 (1 H, d, J 6, 5-H), 5.39 (1 H, m, 6-H), 5.47 (1 H, d, J 10, 8-H), 5.78 (1 H, d, J 10, 7-H), 6.56 and 6.67 (2 H, ABq, 1 and 2-H), 6.83 (2 H, d, J 9, 21 and 23-H), 7.95 (2 H, d, J 9, 20 and 24-H); m z 419 (M\ 20%) 282(19), 229(7), 162(40), 138(32), 121(80), 94(36), 73(32), 65(30), 44(100). (Found M\ 419.1749. C25H25NO5 requires 419.1733).

EXAMPLE 2: SYNTHESIS OF MORPHINE ANALOGUES OF M6G

The synthesis of the compounds described in this Example is shown schematically in Figure 2

Preparation of 3-t-Buty ldimethylsilyloxy-7,8-didehydro-4,5a-epoxy-l 7-methyl- morphinan-6-ol ( 1 )

To a solution of moφhine (2 g, 7 mmol), in THF, under nitrogen, was added NaH-60% dispersion in mineral oil (310 mg, 7.75 mmol) and the reaction stirred for 1 hour. tert-Butyldimethylsilyl chloride (1.27 g, 8.45 mmol) was added and the reaction stirred overnight. The mixture was filtered and THF removed under reduced pressure. The residue was purified by column chromatography (elution with 15% MeOH in CHCI3). A cream powder was obtained (1.445 g, 52%) m.p. 121-22°C (lit. 122-123°C); vmax nujoi cm- ¹ 3552 (OH). 1629; δ _H (CDCI3) 0.16 (3 H, s, SiMe), 0.20 (3 H, s, SiMe), 0.98 (9 H, s, SiCMe ₃ ), 1.89 (1 H, d, J 12, 15e-H), 2.21 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.43 (2 H, m, lOo and 16-H), 2.55 (3 H, s, NMe), 2.75 (1 H, dd, J 12.5, 4, 16-H), 2.89 (1 H, t, J 2.5, 14-H), 3.04 (1 H, d, J 18.5, 10p-H), 3.50 (1 H, q, J 3.5, 9-H), 4.19 (1 H, m, 6-H), 4.87 (1 H, d, J 6.5, 5-H), 5.26 (1 H, d, J 10, 8-H), 5.70 (1 H, d, J 10, 7-H), 6.50 and 6.60 (2 H, ABq, 1 and 2-H); m/z 503 (M\ 15%) 446(10), 324(6), 266(9), 122(8), 105(100), 77(27), 57(16), 41(35). (Found M ⁺ , 503.2446. C3 ₀ H3 ₇ NO ₄ Si requires 503.2492).

Preparation of 6a-Benzoyloxy-3-t-butyldimethylsilyloxy-7,8-didehydro-4,5a- epoxy-17-methyl-morphinan (2 X=H in the relevant part of Figure 2)

To a solution of 3-t-BDMS-moφhine (1) (300 mg, 0.75 mmol) in pyridine (3 cm ³ ) with a little DMAP, under nitrogen, was added benzoyl chloride (0.5 cm ³ , 317 mg, 2.25 mmol) and the reaction stirred at room temperature for 10 minutes. CHCI3 was added and the solution washed successively with 5% CUSO4 solution/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 3% MeOH) in CH2CI2) to give the ester (2 X=H in Figure 2) (336 mg, 89%) m.p. 133-5°C; 1717 (CO); δ _H (CDCl ₃ ) 0.13 (6 H, s, SiMe ₂ ), 0.84 (9 H, s, SiCMe ), 1.93 (1 H, d, J 11, 15e-H), 2.33 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.56 (2 H, m, lOo and 16-H), 2.64 (3 H, s, NMe), 2.95 (1 H, dd, J 12.5, 4, 16-H), 3.09 (2 H, m, lOp and 14-H), 3.71 (1 H, q, J 3.5, 9-H), 5.24 (1 H, d, J 6, 5-H), 5.44 (2 H, m, 6 and 8-H), 5.79 (1 H, d, J 10, 7-H), 6.51 and 6.62 (2 H, ABq, 1 and 2-H), 7.42 (2 H, t, J 7.5 21 and 23-H), 7.56 (1 H, t, J 7.5, 22-H), 8.09 ( 2H, d, J 7, 20 and 24-H).

Preparation of 3-t-Butyldimethylsilyloxy-7,8-didehydro-4,5a-epoxy-6a-(4-flu oro- benzoyloxy)-17-methyl-morphinan (3 X=F in the relevant part of Figure 2 )

To a solution of 3-t-BDMS-moφhine (1) (300 mg, 0.75 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-fluorobenzoyl chloride (0.3 cm ³ , 360 mg, 2.25 mmol) and the reaction stirred at room temperature for 20 minutes. CHCI3 was added and the solution washed successively with 5% CUSO4 solution water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 3% MeOH in CH ₂ C1 ₂ ) to give the ester (3 X=F) (342 mg, 87%) m.p. 134-6°C; ^v maχ( ^CHC1 3) ^{cm" 1 1717} ( ^{C=0 ester} )' ^δ H (CDCI3) 0.04 (6 H, s, SiMe ₂ ), 0.84 (9 H, s, SiCMe ₃ ), 1.90 (1 H, d, J 11, 15e-H), 2.24 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.52 (2 H, m, lOo and 16-H), 2.58 (3 H, s, NMe), 2.85 (1 H, dd, J 12.5, 4, 16-H), 3.01 (1 H, t, J 2.5, 14-H), 3.08 (1 H, d, J 18.5 lOp-H), 3.66 (1 H, q, J 3, 9-H), 5.19 (1 H, d, J 6.5, 5-H), 5.39 (1 H, m, 6-H), 5.48 (1 H, d, J 10, 8-H), 5.76 (1 H, d, J 10, 7-H), 6.50 and 6.61 (2 H, ABq, 1 and 2-H), 7.07 and 7.11 (2 x 1 H, d, J 8.5, 21 and 23-H), 8.08 and 8.12 (2 x 1 H, d, J 8.5, 20 and 24-H); δ _c -4.85, 18.06, 21.1 1, 25.51, 34.56, 39.55, 42.16 (NMe), 42.71, 46.39, 58.90,

69.16, 87.79, 115.24, 115.59, 119.31, 121.71, 126.11, 128.80, 129.04, 130.11, 131.96,

132.52, 132.52, 132.67, 137.76, 149.03, 163.86. 168.86, 168.12; m z 521 (M\ 14%) 464(9), 382(5), 324(4), 284(5), 140(20), 123(100), 95(28), 73(21), 59(9), 42(11). (Found M\ 521.2413. C3 ₀ H ₃₆ NFO ₄ Si requires 521.2398).

Preparation of 3-t-Butyldimethylsilyloxy-6a-(4-chlorobenzoyloxy)-7,8-didehy dro-

4,5a-epoxy-17-methyl-morphinan (4 X=C1 in the relevant part of Figure 2)

To a solution of 3-t-BDMS-moφhine (1) (300 mg, 0.75 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-chlorobenzoyl chloride (0.3 cm ³ , 396 mg, 2.25 mmol) and the reaction stirred at room temperature for 5 minutes. CHCI3 was added and the solution washed successively with 5% CUSO4 solution water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 3% MeOH in CH ₂ C1 ₂ ) to give the ester (4 X=-CI) (381 mg, 94%) m.p. 119-21°C; 1719 (C=O ester); δ _H (CDCl ₃ ) 0.05 (6 H, s, SiMe ₂ ), 0.85 (9 H, s, SiCMe ₃ ), 1.84 (1 H, d, J 1 1, 15e-H), 2.05 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.34 (2 H, m, lOo and 16-H), 2.45 (3 H, s, NMe), 2.57 (1 H, dd, J 12.5, 4, 16-H), 2.77 (1 H, t, J 2.5, 14-H),

3.04 (1 H, d, J 18.5, lOp-H), 3.38 (1 H, q, J 3.5, 9-H), 5.16 (1 H, d, J 6.5 5-H), 5.39 (1 H, m, 6-H), 5.48 (1 H, d, J 10, 8-H), 5.72 (1 H, d, J 10, 7-H), 6.47 and 6.58 (2 H, ABq, 1 and 2-H), 7.41 (2 H, d, J 8.5, 21 and 23-H), 8.01 (2 H, d, J 8.5, 20 and 24-H), δ _c -4.78, 18.31. 21.46, 25.03, 32.76, 37.64, 40.86 (NMe), 41.56, 46.50, 59.50, 68.39, 86.77, 119.47, 122.11, 127.01, 128.08, 128.38, 129.29, 130.89, 131.11, 137.76, 139.45, 148.03, 164.76; m/z 539 and 537 (M\ 23 and 55%) 482(13), 480(34), 456(15), 413(13), 382(25), 324(18), 300(14), 266(14), 141(35), 139(91), 123(7), 94(10), 73(100), 59(36), 42(48). (Found M\ 539.2070 and 537.2123. C ₃ oH3 ₆ NClO ₄ Si requires 539.2072 and 537.2102).

Preparation of 6a-(4-Bromobenzoyloxy)-3-t-butyldimethylsilyoxy-7,8-didehydr o-

4,5a-epoxy-17-methyl-morphinan (5 X=Br in the relevant part of Figure 2)

To a solution of 3-t-BDMS-moφhine (1) (300 mg, 0.75 mmol) in pyridine (3 cm ³ ) with a little DMAP, under nitrogen, was added p-bromobenzoyl chloride (825 mg,

3.75 mmol) and the reaction stirred at room temperature for 20 minutes. CHCI3 was added and the solution washed successively with 5% CUSO4 solution/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column

chromatography (elution with 3% MeOH in CH2CI2) to give the ester (5 X=Br) (315 mg, 72%) m.p. 137-8°C; v _max (CKCl3)lcm- ¹ 1719 (C=O ester); δ _H (CDCI3) 0.01 (3 H, s, SiMe), 0.04 (3 H, s, SiMe), 0.84 (9 H, s, SiCMe ₃ ), 1.87 (1 H, d, J 11, 15e-H), 2.15 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.40 (2 H, m, lOo and 16-H), 2.47 (3 H, s, NMe), 2.72 (1 H, dd, J 12, 4, 16-H), 2.88 (1 H, t, J 2.5, 14-H), 3.06 (1 H, d, J 18.5, lOp-H), 3.50 (1 H, q, J 3, 9-H),

5.17 (1 H, d, J 6.5, 5-H), 5.38 (1 H, m, 6-H), 5.48 (1 H, d, J 10, 8-H), 5.73 (1 H, d, J 10, 7-H), 6.49 and 6.59 (2 H, ABq, 1 and 2-H), 7.56 (2 H, d, J 8.5, 21 and 23-H), 7.95 (2 H, d, J 8.5, 20 and 24-H); m z 583 and 581 (M\ 22 and 22%) 527(15), 525(14), 382(19), 266(15), 202(29), 200(30), 185(96), 183(100), 155(31), 123(41), 105(33), 75(50), 73(62), 51(56), 41(58).

(Found M\ 583.1641 and 581.1603. C ₃₀ H3 ₆ NBrO ₄ Si requires 583.1578 and 581.1597).

Preparation of 3-t-Butyldimethylsilyloxy-7,8-didehydro-4,5a-epoxy-17-methyl -6a- (4-nitrobenzoyloxy)-morphinan (6 X=NO2 in the relevant part of Figure 2) To a solution of 3-t-BDMS-moφhine (1) (150 mg, 0.37 mmol) in pyridine (5 cm ³ ) with a little DMAP, under nitrogen, was added p-nitrobenzoyl chloride (210 mg, 1.13 mmol) and the reaction stirred overnight. EtOAc was added and the solution washed with 5% CUSO4 solution/water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 10% MeOH in CHCI3) to give the ester (6 1718 (C=O ester); δ _H (CDCI3) 0.03 (3 H, s, SiMe), 0.06 (3 H, s, SiMe), 0.85 (9 H, s, SiCMe3), 1.89 (1 H, d, J 11, 15e-H), 2.13 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.40 (2 H, m, 10a and 16-H), 2.50 (3 H, s, NMe), 2.65 (1 H, dd, J 12.5, 4, 16-H), 2.85 (1 H, t, J 2.5, 14-H), 3.10 (1 H, d, J 18.5, lOp-H), 3.44 (1 H, q, J 3, 9-H), 5.20 (1 H, d, J 6.5, 5-H), 5.43 (1 H, m, 6-H), 5.54 (1 H, d, J 10, 8-H), 5.75 (1 H, d, J 10, 7-H), 6.49 and 6.59 (2 H, ABq, 1 and 2-H), 8.29 (4 H, s, 20, 21, 23 and 24-H); δ _C -4.92, 17.96, 20.36, 25.35, 35.43, 40.71, 42.87, 42.95 (NMe), 46.51, 58.91, 69.85, 87.37, 119.19, 121.23, 123.29, 127.27, 127.49, 130.27, 130.43, 131.01, 135.29, 137.06, 148.42, 150.48, 163.98; m z 548 (M\ 52%) 491(38), 382(25), 266(21), 137(18), 122(14), 104(40), 92(20), 77(45), 50(79), 41(100). (Found M\ 548.2331. C ₃₀ H3 ₆ N ₂ O ₆ Si requires 548.2342).

Preparation of 3-t-Butyldimethylsilyloxy-7,8-didehydro-4,5a-epoxy-6a-(4-met hoxy- benzoyloxy)-17-methyl-morphinan (7 X-ome in the relevant part of Figure 2)

To a solution of 3-t-BDMS-moφhine (1) (100 mg, 0.25 mmol) in pyridine (3 cm ³ ), under nitrogen, was added p-anisoyl chloride (0.1 cm ³ , 128 mg, 0.75 mmol) and the reaction stirred at room temperature for 30 minutes. EtOAc was added and the solution washed successively with dilute HCl/water/bicarbonate/water, dried (MgSO4), and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in CHCI3) to give the ester (7 X=ome) (82 mg, 61%) m.p. 173-5°C; v-na _j JCHC /cπr ¹ 1710 (C=O ester); δ _H (CDCl ₃ ) 0.04 (3 H, s, SiMe), 0.06 (3 H, s, SiMe), 0.87 (9 H, s, SiCMe ₃ ), 1.88 (1 H, d, J 1 1, 15e-H), 2.10 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.38 (2 H, m, lOo and 16-H), 2.46 (3 H, s, NMe), 2.61 (1 H, dd, J 12.5, 4, 16-H), 2.80 (1 H, t, J 2.5, 14-H), 3.05 (1 H. d, J 18.5, lOp-H), 3.40 (1 H, q, J 3, 9-H), 3.87 (1H, s, O-Me), 5.17 (1 H, d, J 6.5, 5-H), 5.38 (1 H, m, 6-H), 5.45 (1 H, d, J 10, 8-H), 5.73 (1 H, d, J 10, 7-H), 6.47 and 6.59 (2 H, ABq, 1 and 2-H), 6.90 (2 H, d, J 9, 21 and 23-H), 8.06 (2 H, d, J 9, 20 and 24-H); m/z 533 (M\ 8%) 476(4), 382(3), 324(4),

296(4), 152(5), 135(100), 92(4), 73(11), 51(9), 41(10). (Found M ⁺ , 533.2602. C ₃₁ H39NO ₅ Si requires 533.2598).

Preparation of 3-t-Butyldimethylsilyloxy-6a-(4-t-butyldimethylsilyloxybenzo yloxy)- 7,8-didehydro-4,5a-epoxy-17-methyl-morphinan (8 V=OTBDMS in the relevant part of Figure 2)

Freshly prepared p-t-BDMS-oxy benzoic acid (500 mg, 1.98 mmol) in DCM (5 cm ³ ), under nitrogen, was treated with oxalyl chloride (630 mg, 0.43 cm ³ , 5 mmol). Effervescence implied formation of the acid chloride. On completion of the reaction, after 20 minutes, benzene (5 cm ³ ) was added and all solvents removed under reduced pressure. To the acid chloride residue, under nitrogen, was added a solution of 3-t-BDMS-moφhine (1) (250 mg, 0.63 mmol) in pyridine (3 cm ³ ) and the reaction stirred at room temperature overnight. EtOAc was added and the solution washed with dilute HCl/water/bicarbonate/water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by column chromatography (elution with 5% MeOH in DCM) to give the ester (8 X=OTBDMS) (276 mg, 70%) m.p. 122-4°C; δ _H (CDCI3) 0.02 (3 H,

s, SiMe), 0.04 (3 H, s, SiMe), 0.17 (6 H, s, SiMe ₂ ) 0.82 (9 H, s, SiCMe ₃ ), 0.94 (9 H, s, SiCMe ₃ ), 1.83 (1 H, d, J 11, 15e-H), 2.07 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.34 (2 H, m, lOo and 16-H), 2.42 (3 H, s, NMe), 2.58 (1 H, dd, J 12, 4, 16-H), 2.78 (1 H, t, J 2.5, 14-H), 3.00 (1 H, d, J 18.5, lOp-H), 3.39 (1 H, q, J 3, 9-H), 5.13 (1 H, d, J 6.5, 5-H), 5.31 (1 H, m, 6-H), 5.40 (1 H, d, J 10, 8-H), 5.68 (1 H, d, J 10, 7-H), 6.42 and 6.53 (2 H, ABq, 1 and 2-H), 6.80 (2 H, d, J 9, 21 and 23-H), 7.94 (2 H, d, J 9, 20 and 24-H).

Preparation of 3-t-Butyldimethylsilyloxy-7,8-didehydro-4,5a-epoxy-17-methyl - 6a-succinyloxy-morphinan (9) A mixture of 3-t-BDMS-moφhine (1) (300 mg, 0.75 mmol) and succinic anhydride

(375 mg, 3.75 mmol) in pyridine (5 cm ³ ), under nitrogen, was refluxed for 1 hour. The hot reaction mixture was poured onto ice and the resulting white precipitate collected on a filter. The precipitate was washed with cold water. Crystallisation from DCM-petroleum ether gave the ester (9) (225 mg, 60%) m.p. 144-7°C; 1735 (C=O ester), 1604 (C=O acid); δ _H (CDC1 ₃ ) 0.15 (3 H, s, SiMe), 0.20 (3 H, s, SiMe),

0.98 (9 H, s, SiCMe ₃ ), 1.86 (1 H, d, J 12, 15e-H), 2.41-2.82 (10 H, m, N-Me, 2xCH ₂ , 10a, 15o and 16-H), 3.00 (1 H, d, J 18.5, lOp-H), 3.10 (2 H, m, 14 and 16-H), 3.79 (1 H, q, J 3.5, 9-H), 5.09 (1 H, d, J 6, 5-H), 5.28 (2 H, m, 6 and 8-H), 5.56 (1 H, d, J 10, 7-H), 6.47 and 6.61 (2 H, ABq, 1 and 2-H); δ _c -4.78, -4.55, 18.15, 21.19, 25.66, 30.18, 30.95, 33.20, 37.63, 40.92 (NMe), 42.01, 46.16, 58.66, 68.08, 88.18, 119.19, 122.01, 124.45, 127.71, 129.60, 129.94, 137.80, 148.62, 172.70, 172.85; m z 499 (M ⁺ , 3%) 456(5), 382(9), 324(1 1), 267(12), 215(29), 105(24), 73(100), 41(94). (Found M\ 499.2388. C ₂ 7H ₃₇ NO ₆ Si requires 499.2390).

Preparation of 3-t-Butyldimethylsilyloxy-6a-(2-carboxybenzoyloxy)- 7,8-didehydro-4,5a-epoxy-l 7-methyl-morphinan (10)

A mixture of 3-t-BDMS-moφhine (1) (250 mg, 0.63 mmol) and phthalic anhydride

(500 mg, 3.38 mmol) in pyridine (2 cm ³ ), under nitrogen, was refluxed for 1 hour. The hot reaction mixture was poured onto ice and the resulting white precipitate collected on a filter. The precipitate was washed with cold water. Crystallisation from DCM-petroleum ether gave the ester (10) (237 mg, 69%) m.p. 193-5°C (decomp); v _maχ (CHCl ₃ )/cm- ¹

1714 (C=O ester), 1602 (C=O acid); δ _H (CDC1 ) 0.04 (3H, s, SiMe), 0.06 (3 H, s, SiMe), 0.88 (9 H, s, SiCMe ₃ ), 1.97 (1 H, d, J 11, 15e-H), 2.78-2.88 (3 H, m, 10a, 15o and 16-H), 2.91 (3 H, s, NMe), 3.08 (1 H, d, J 18.5, lOp-H), 3.45 (1 H, dd, J 12, 4, 16-H), 3.59 (1 H, t, J 2.5, 14-H), 4.03 (1 H, q, J 3.5, 9-H), 5.32 (1 H, d, J 6.5, 5-H), 5.40 (1 H, d, J 10, 8-H), 5.55 (1 H, m, 6-H), 5.80 (1 H, d, J 10, 7-H), 6.54 and 6.66 (2 H, ABq, 1 and 2-H), 7.38 (1 H, t, J 7.5, 22-H), 7.52 (1 H, t, J 7.5, 23-H), 7.66 (1 H, d, J 7.5, 21-H), 7.92 (1 H, d, J 7.5, 24-H).

Preparation of 6a-Benzoy loxy-7,8-didehydro-4,5a-epoxy-l 7-methy 1-morphinan- 3-ol (11 X=H in the relevant parts of Figure 2)

To a solution of the ester (2) (150 mg, 0.27 mmol) in dry THF (3 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was dissolved in EtOAc and washed with water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by TLC to give the ester (11 X-=H), a white powder, (102 mg, 88%). Crystallisation was from CHCl ₃ /MeOH. m.p. 264-8°C (decomp); (found C, 73.25; H, 5.85; N, 3.65. C24H23NO4 requires C, 73.2; H, 5.95; N, 3.55%); ^v ma _χ ( ^nu J° ¹ )/cm- ¹ 1713 (C=O ester); δ _H (CD ₃ OD/CDCl ₃ ) 1.88 (1 H, d, J 12.5, 15e-H), 2.08 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.37 (2 H, m, lOo and 16-H), 2.44 (3 H, s, NMe), 2.61 (1 H, dd, J 12.5, 4, 16-H), 2.80 (1 H, t, J 2.5, 14-H), 3.04 (1 H, d, J 18.5, 10p-H), 3.38 (1 H, q, J 3, 9-H), 5.21 (1 H, d, J 6.5, 5-H), 5.41 (1 H, m, 6-H), 5.49 (1 H, d, J 10, 8-H), 5.76 (1 H, d, J 10, 7-H), 6.52 and 6.63 (2 H, ABq, 1 and 2-H), 7.45 (2 H, t, J 8, 21 and 23-H), 7.59 (1 H, t, J 7.5, 22-H), 8.10 (2 H, d, J 7, 20 and 24-H); δ _c 20.30, 34.92, 40.23, 42.71 (NMe), 46.58, 58.98, 68.74, 88.07, 116.69, 119.63, 125.34, 128.16, 128.35, 129.46, 129.58, 129.71, 129.71, 129.92, 133.20, 138.27, 144.94, 166.24; m/z 389 (M ⁺ , 38%) 268(33), 215(13), 146(12), 122(11), 105(100), 94(6), 77(34). (Found M ⁺ , 389.1623. C24H23NO4 ^rec l ^{uires 3} 89.1627).

Preparation of 7,8-Didehy dro-4,5a-epoxy-6a-(4-fluorobenzoy loxy)-l 7-methy I- morphinan-3-ol (12 X=F in the relevant parts of Figure 2)

To a solution of the ester (3) (150 mg, 0.29 mmol) in dry THF (3 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was dissolved in EtOAc and washed with water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by TLC to give the ester (12 X=F), a white powder, (96 mg, 82%). Crystallisation was from CHCl ₃ /MeOH. m.p. 279-83°C (decomp); (Found: C, 70.45; H, 5.4; N, 3.3. C24H22NFO4 requires C, 70.75; H, 5.45; N, 3.45%); 1713 (C=O ester); δ _H (CD ₃ OD/CDCl3) 1.88 (1 H, d, J 11, 15e-H), 2.06 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.37 (2 H, m, lOo and 16-H), 2.45 (3 H, s, NMe), 2.62 (1 H, dd, J 12.5, 4, 16-H), 2.80 (1 H, t, J 2.5, 14-H), 3.04 (1 H, d, J 18.5, lOp-H), 3.38 (1 H, q, J 3.5, 9-H), 5.18 (1 H, d, J 6.5, 5-H), 5.40 (1 H, m, 6-H), 5.50 (1 H, d, J 10,7-H), 6.51 and 6.62 (2 H, ABq, 1 and 2-H), 7.1 1 and 7.15 (2 x 1 H, d, J 8.5, 21 and 23-H), 8.09 and 8.11 (2 x 1 H, d, J 8.5, 20 and 24-H); δ _c 21.28, 34.77, 40.06, 42.59 (NMe), 46.56, 58.95, 68.66, 87.84, 115.21, 115.56, 116.64, 119.53, 125.15, 128.10, 129.39, 129.86, 132.26, 132.41, 138.36, 145.03, 163.80, 165.32, 167.84; m z 407 (M\ 30%) 284(17), 268(33), 215(14), 146(13), 123(100), 95(31), 84(21). (Found M\ 407.1593. C24H22NFO4 requires 407.1533).

Preparation of 6a-(4-Chlorobenzoyloxy)-7,8-didehydro-4,5a-epoxy-l 7-methy I- morphinan-3-ol (13 X— CI in the relevant parts of Figure 2)

To a solution of the ester (4) (150 mg, 0.28 mmol) in dry THF (3 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was dissolved in EtOAc and washed with water, dried (Na SO4) and evaporated under reduced pressure. The crude product was purified by TLC to give the ester (13 X-Cl) 105 mg, 89%). Crystallisation was from CHC^/MeOH. m.p. 269-72°C (decomp); (Found: C, 67.7; H, 5.2; N, 3.25. C24H22NCIO4 requires C, 68.0; H, 5.25; N, 3.3%); 1719 (C=O ester); δ _H (CD ₃ OD/CDCl ₃ ) 1.95 (1 H, d, J 12, 15e-H), 2.29 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.57 (2 H, m, lOo and 16-H),

2.66 (3 H, s, NMe), 3.04 (3 H, m, 10p, 14 and 16-H), 3.75 (1 H, q, J 3, 9-H), 5.22 (1 H, d, J 6.5, 5-H), 5.41 (1 H, m, 6-H), 5.51 (1 H, d, J 10, 8-H), 5.79 (1 H, d, J 10, 7-H), 6.55 and 6.65 (2 H, ABq, 1 and 2-H), 7.39 and 7.42 (2 x 1 H, d, J 8.5, 21 and 23-H), 7.98 and 8.01 (2 x 1 H, d, J 8.5, 20 and 24-H); m/z 423 and 425 (M\ 36 and 12%) 300(8), 268(54), 215(21), 141(34), 139(100), 111(32), 94(10), 81(17).

(Found M ⁺ , 425.1207 and 423.1237. C24H22NCIO4 requires 425.1227 and 423.1268).

Preparation of 6a-(4-Bromobenzoyloxy)-7,8-didehydro-4,5a-epoxy-l 7-methyl- morphinan-3-ol (14 X-Br in the relevant parts of Figure 2) To a solution of the ester (5) (150 mg, 0.26 mmol) in dry THF (3 cm ³ ), under nitrogen, at 0°C, was added TBAF (1M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was dissolved in EtOAc and washed with water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by TLC to give the ester (14 X=Br), a white powder, (97 mg, 80%).

Crystallisation was from CHCl ₃ /MeOH. m.p. 279-84°C (decomp); (Found: C, 61.25; H, 4.7; N, 3.05. C ₂ 4H ₂ 2NBrO ₄ requires C, 61.5; H, 4.7; N, 3.0%); 1718 (C=O ester); δ _H (CD ₃ OD/CDCl ₃ ) 1.88 (1 H, d, J 12.5, 15e-H), 2.08 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.37 (2 H, m, lOo and 16-H), 2.46 (3 H, s, NMe), 2.62 (1 H, dd, J 12.5, 4, 16-H), 2.81 (1 H, t, J 2.5, 14-H), 3.04 (1 H, d, J 18.5, 10p,-H), 3.40 (1 H, q, J 3, 9-H),

5.18 (1 H, d, J 6.5, 5-H), 5.40 (1 H, m, 6-H), 5.51 (1 H, d, J 10, 8-H), 5.74 (1 H, d, J 10, 7-H), 6.51 and 6.63 (2 H, ABq, 1 and 2-H), 7.60 (2 H, d, J 8.5, 21 and 23-H), 7.95 (2 H, d, J 8.5, 20 and 24-H); m/z 469 and 467 (M\ 39 and 42%) 268(95), 215(36), 185(92), 183(100), 155(42), 141(23), 94(17), 81(32). (Found M\ 469.0544 and 467.0583. C24H22NB1 4 requires 469.0713 and 467.0733).

Preparation of 7,8-Didehydro-4,5a-epoxy-l 7-methy l-6a-(4-nitrobenzoyloxy )- morphinan-3-ol (15 in the relevant parts of Figure 2)

To a solution of the ester (6) (300 mg, 0.18 mmol) in dry THF (5 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring

continuing overnight. The reaction mixture was evaporated under reduced pressure. The crude product was purified by TLC to give the ester (15 X=NO2), a yellow powder, (206 mg, 87%). Crystallisation was from DMSO/H ₂ O. m.p. 260-9°C (decomp); (Found: C, 64.0; H, 5.4; N, 5.95. C ₂ 4H ₂ 2N2O ₆ requires C, 63.7; H, 5.35; N, 6.2%); v _j naxtnujoiycm ^"1 1719 (C=O ester); δ _H (DMSO-d ₆ ) 1.62 (1 H, d, J 11, 15e-H),

2.06 (1 H, dt, J 12.5, 5, 5, 15a-H), 2.21 (2 H, m, 10a and 16-H), 2.31 (3 H, s, NMe), 2.48 (1 H, m, 16-H), 2.76 (1 H, t, J 2.5, 14-H), 2.89 (1 H, d, J 18.5, lOp-H), 3.31 (1 H, q, J 3, 9-H), 5.12 (1 H, d, J 6.5,5-H), 5.43 (1 H, m, 6-H), 5.55 (1 H, d, J 10, 8-H), 5.72 (1 H, d, J 10, 7-H), 6.41 and 6.47 (2 H, ABq, 1 and 2-H), 8.22 (2 H, d, J 9, 20 and 24-H), 8.36 (2 H, d, J 9, 21 and 23-H); δ _c 19.90, 34.85, 39.94, 42.12, 42.78 (NMe), 46.32, 58.27, 69.38, 86.84, 1 16.48, 119.16, 123.87, 125.18, 127.64, 130.46, 130.53, 130.98, 135.32, 138.88, 145.14, 150.36, 163.90; m/z 434 (M ⁺ , 14%) 268(15), 248(16), 136(11), 104(17), 91(21), 88(19), 44(100). (Found M ⁺ , 434.1479. C ₂ 4H ₂ 2N ₂ O ₆ requires 434.1478).

Preparation of 7,8-Didehydro-4,5a-epoxy-6a-(4-hydroxybenzoyloxy)-17-methyl- morphinan-3-ol (16 X=OH in the relevant parts of Figure 2)

To a solution of the ester (8) (500 mg, 0.79 mmol) in dry THF (5 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (2 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was dissolved in EtOAc and washed with water, dried (Na2SO4) and evaporated under reduced pressure. The crude product was purified by TLC to give the ester (16 X=OH) (268 mg, 84%). Crystallisation was from CHCl ₃ /MeOH. m.p. 178-82°C (decomp); (Found: C, 68.1 ; H, 5.65; N, 3.2. C24H23NO5 requires C, 68.1; H, 5.9; N, 3.3%); 1715 (C=O ester); δ _H (CD ₃ OD/CDCl ) 1.81 (1 H, d, J 11.5, 15e-H), 2.05 (1 H, dt, J 12.5, 5, 5, 15a-H),

2.34 (2 H, m, lOo and 16-H), 2.43 (3 H, s, NMe), 2.61 (1 H, dd, J 12.5, 4, 16-H), 2.79 (1 H, t, J 2.5, 14-H), 3.02 (1 H, d, J 18.5, 10p,-H), 3.38 (1 H, q, J 3, 9-H), 5.15 (1 H, d, J 6, 5-H), 5.34 (1 H, m, 6-H), 5.46 (1 H, d, J 10, 8-H), 5.73 (1 H, d, J 10, 7-H), 6.50 and 6.63 (2 H, ABq, 1 and 2-H), 6.85 (2 H, d, J 9, 21 and 23-H), 7.95 (2 H, d, J 9, 20 and 24-H); δ _c 20.38, 34.68, 39.94, 42.48 (NMe), 42.62. 46.56, 58.94, 68.27, 88.15, 115.30, 1 16.78, 119.58, 120.47, 125.27, 128.48, 129.19, 129.97, 132.04, 138.28. 145.02, 162.06, 166.27;

m/z 405 (M ⁺ , 11%) 285(14), 210(14), 155(15), 138(23), 121(84). 94(100), 65(42), 51(28), 44(49). (Found M\ 405.1569. C24H23NO5 requires 405.1576).

Preparation of 7,8-didehydro-4,5a-epoxy-l 7-meth l-6a-succinyloxy- morphinan-3-ol (17)

To a solution of the ester (9) (150 mg, 0.3 mmol) in THF (2 cm ³ ), under nitrogen, at 0°C, was added TBAF (1 M solution in THF) (1 cm ³ ). The reaction was stirred at 0°C for 5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was quenched with water. The resulting precipitate was collected on a filter giving the acid/ester (17) (62 mg, 54%). Crystallisation was from CHCl ₃ /MeOH. m.p. 275-9°C (decomp); 3382 (OH), 1736 (C=O ester), 1605 (C=O acid); δ _H (CD ₃ OD/CDCl ₃ ) 1.96 (1 H, d, J 12, 15e-H), 2.43-2.86 (10 H, m, N-Me, 2xCH ₂ , lOo, 15a, and 16-H), 3.04 (1 H, d, J 18.5, lOp-H), 3.15 (2 H, m, 14 and 16-H), 3.83 (1 H, q, J 3.5, 9-H), 5.11 (1 H, d, J 6, 5-H), 5.30 (2 H, m, 6 and 8-H), 5.58 (1 H, d, J 10, 7-H), 6.57 and 6.61 (2 H, ABq, 1 and 2-H).

Preparation of 6a-(2-Carboxybenzoyloxy)-7,8-didehydro-4,5a-epoxy- 17-methy l-morphinan-3-ol (18)

To a solution of the ester (10) (300 mg, 0.18 mmol) in pyridine (5 cm ³ ), under nitrogen, at 0°C, was added HF-pyridine (1 cm ³ ). The reaction was stirred at 0°C for

5 minutes and then allowed to warm up to room temperature, with stirring continuing overnight. The reaction mixture was quenched with water. The resulting precipitate was collected on a filter giving the acid/ester (18) (135 mg, 57%). Crystallisation was from

CHCl ₃ /MeOH. m.p. 225-8°C (decomp); (Found: C, 65.5; H, 5.35; N, 2.85. C ₂ 5H ₂ 3NO ₆ requires C, 65.2; H, 5.65; N, 3.05%); 3398 (OH), 1716 (C=O ester),

1601 (C=O acid); δ _H (CD ₃ OD/CDCl ) 2.03 (1 H, d, J 10, 15e-H), 2.90 (3 H, m, lOo, 15a and 16-H), 3.01 (3 H, s, NMe), 3.21 (1 H, d, J 18.5, lOp-H), 3.48 (1 H, d, J 8, 16-H),

3.86 (1 H, t, J 2.5, 14-H), 4.12 (1 H, q, J 3, 9-H), 5.53 (2 H, m, 6 and 8-H), 5.66 (1 H, d,

J 6.5, 5-H), 5.91 (1 H, d, J 10, 7-H), 6.59 and 6.63 (2 H, ABq, 1 and 2-H), 7.40 (1 H, m, 22-H), 7.56 (2 H, m, 21 and 23-H), 7.92 (1 H, d, J 7.5, 23-H); m/z (M\ 433) 285(100),

268(1 1), 215(21), 162(29), 124(17), 104(96), 76(79), 42(31).

IN VIVO EXPERIMENTS

EXAMPLE 3: OPIOID RECEPTOR PROFILE

Solutions

Tris buffer was prepared as 50mM in distilled water and the pH adjusted to 7.4 with HC1(4N). Tris-NaCl buffer contained 1 OOmM NaCl.

Krebs buffer solution for the myenteric plexus longitudinal muscle (MPLM) comprised the following :-

NaCl (6.92g/l), KC1 (0.35g/l), KH ₂ PO ₄ (0.16g/l), CaCl ₂ .2H ₂ O (0.375g/l for MPLM and 0.188g/l for RVD), NaHCO ₃ (2.1g/l), MgSO ₄ .7H ₂ O (0.29g/l) and glucose (2g/l). The buffer was gassed with 95% O ₂ , 5% CO ₂ .

Krebs solution for the mouse vas deferens (MVD) preparation was as above, but with the omission of MgSO4.7H ₂ O (Ward et al, 1986, J. Pharmacol. Exp. Ther., ___., 625- 634). Krebs/HEPES buffer was made up as Krebs buffer (above) with HEPES at a concentration of 25mM adjusted to pH 7.4 with 0.88M ammonia solution. ________

Ligand binding assays Brain homogenates

Brains were removed from male CSI mice (discarding the cerebellum) and homogenised in Tris buffer (50mM, pH 7.4) at 10% tissue w/v. The homogenate was centrifuged at 25,500g for 20 mins. The supernatant was discarded and the pellet resuspended in buffer. The suspension was incubated at 37 ^β C for 30 mins, then recentrifuged. The pellet obtained was resuspended in buffer to obtain a 1 :60 tissue w/v ratio. This dilution corresponds to a protein concentration of approximately lmg/ml as determined by Lowry's method (Lowry et /., 1951, J. Biol. Chem., 19_2, 265-275). For saturation binding assays tubes were set up containing 20μl of tritiated ligand and 960μl of brain homogenate in a total volume of 1ml. 20μl of naloxone (lOμM) was added to each tube to determine the non-specific binding. For competition assays tubes contained labelled ligand (usually l.OnM final concentration) plus increasing concentrations of competing cold ligand, or 20μl of water or 20μl of naloxone (lOμM), which represented the total bound ligand and non-specifically bound ligand values respectively. Assay tubes were incubated at 25 °C for 40 mins, unless stated otherwise. At

the end of the incubation period the tube contents were filtered through glass filter papers (Whatman GFB) which were presoaked in either Tris buffer pH 7.4 or Tris-buffer pH 7.4 containing polyethyleneimine (0.1%) to reduce non-specific binding to filters. The tubes were washed three times with 3ml of ice cold Tris buffer and the washings were also filtered. The filters were placed in scintillation vials, ecoscint scintillant fluid added, and the filters soaked for 8 hours. The radioactivity remaining on the filters was counted in a Minaxi Tricarb 4000 Series Liquid Scintillation Counter at an efficiency of 58%.

Binding parameters Kp and B^^ were obtained using the LIGAND programme, following Scatchard analysis using the EBDA programme (McPherson, 1985, J. Pharmacol. Meth., 14, 213-228). IC50 values for competing ligands were determined using a logistic curve fitting programme developed by Barlow (1991, Ash Lea Cottage, Ravenstonedale, Kirkby Stephen, Cumbria. Foundations of pharmacology-computer curve fitting programme, publisher, Barton 1991). Isolated tissue studies Tissue preparation a) Guinea-pi? mventeric plexus-longitudinal muscle (MPLMϊ bioassav

Male Dunkin-Hartley guinea-pigs (400-500g) were killed by cervical dislocation. The ileum was removed and immediately placed inaerated Krebs solution at room temperature (Ward et al., 1986, J. Pharmacol. Exp. Ther., ___,, 625-634). After flushing out the contents, strips of myenteric plexus longitudinal muscle (MPLM) were removed and mounted, under a tension of lg, in 3 ml organ baths previously coated with silicon to reduce adsoφtion of peptides onto the glass surface. Tissues were bathed in Krebs solution at 37°C, aerated with 5% CO2 in 95% O2. After allowing a recovery period of 1 h, each tissue was stimulated through platinum ring electrodes using square wave pulses at supramaximal voltage at a frequency of 0.16Hz and a pulse width of 400μs. b) Mouse vas deferens (MVDϊ preparation

Male CSI mice (930-50g), were killed by cervical dislocation. The vasa deferentia were removed immediately, and mounted under a tension of 0.5g in 1.8ml organ baths, previously coated with silicon to reduce adsoφtion losses of peptides. Tissues were bathed in Krebs without MgSO4 at 37°C, aerated with 5% CO2 in 95% O . After allowing a recovery period of 1 h, each vas deferens was stimulated through platinum ring electrodes

using a train of 3 square wave pulses of 1ms duration and 250ms delay at supramaximal voltage at a frequency of 0.1 Hz. Experimental

For all in vitro preparations the same procedure was performed as follows:- a) Agonist potencies

Agonists were added to the organ baths in a cumulative way such that when the response to any one dose reached a maximum the next dose was administered, until approximately 80% inhibition of twitch height was attained after about four cumulative doses. The tissues were washed by overflow with Krebs solution until the original twitch height was restored. The potency of agonists was assessed by measurement of IC5Q'S, the concentration of agonist causing 50% inhibition of the electrically evoked twitch. b) Antagonist affinities

Antagonists were preincubated with the appropriate tissue for 15 mins, prior to the addition of an agonist. Dose-response curves for agonists were obtained before the addition of an antagonist and then repeated in the presence of varying concentrations of the antagonist (normally 10, 30, 100nM)> Dose-ratios were calculated at 50% inhibition and Schild plots constructed. Antagonists were removed from the tissue by continuous washing until the response to the added agonist was fully recovered. In some experiments antagonist Ke values were calculated using a single-dose method. The antagonist equilibrium dissociation constant (Ke) is a measure of affinity and was determined for a partial agonist in the rat vas deferens by pre-incubating the test compound for 15 mins and observing the effect on the dose-response curve for the full μ agonist DAMGO. Antagonist equilibrium dissociation constants (Ke) were obtained by analysing the results according to Kosterlitz and Watt (1968, Br. J. Pharmacol. Chemother., 21, 266-276). Results

Opioid Receptor Profile - Morphine and mornhine-6-glucuronide

The puφose of this experiment was to test analogues of moφhine-6-glucuronide for their selectivity for different opioid binding sites. Ligands which have relative selectivity for different opioid binding sites are well known. The affinities of some illustrative compounds, DAMGO ([D-Ala ² , MePhe ⁴ ,Gly-ol ⁵ ]encephalin, DPDPE

([D- Pen ² ,D-Pen^]encephalin) and U69593 which have high affinities and are selective for

the opioid μ-, δ-, and K- binding sites respectively are shown in Table 1 below:

Table 1: Affinities of opiates and specific ligands at mu, delta and kappa binding sites in mouse brain homogenates.

Ki (nM)

Compound μ δ K

moφhine 6.22 ± 0.86 218.0 ± 41.2 84.7 ± 4.01 moφhine-6-glucuronide 7.90 ± 1.48 75.1 ± 15.6 850 ± 118 moφhine-3-glucuronide > 10,000 > 10,000 > 10,000

DAMGO 2.45 ± 0.40 423.0 ± 7.9 1267 ± 265

DPDPE > 10,000 4.76 ± 1.44 600 ± 124

U69593 > 10,000 > 10,000 2.51 ± 1.22

At the 3 opioid binding sites, moφhine and M6G demonstrate the highest affinity for, and are approximately equipotent at, the μ-site (Table 1). The profile of moφhine and M6G affinities differ, however, at the δ- and K- sites, M6G being approximately 3 -fold more potent at -sites and 10-fold less potent at K- sites than moφhine.

The actions of moφhine and M6G on 2 isolated tissue preparations, namely the guinea-pig myenteric plexus-longitudinal muscle (MPLM) and the mouse vas deferens (MVD) are shown in Table 2. M6G is slightly more potent than moφhine (approximately 2-fold) in both preparations. Also on both isolated tissues, the concentration of naloxone required to antagonise moφhine and M6G to the same degree Ke) is equivalent and similar to that required to antagonise the selective μ-receptor ligand DAMGO (approximate Ke) naloxone = 3nM in each case). Thus the agonists actions of moφhine and M6G on the MPLM and MVD are due to actions at the μ-receptor in both isolated tissue preparations. Relatively higher concentrations of naloxone are required to antagonise δ-mediated effects (DPDPE on the MVD, Ke naloxone = 20.4nM) and κ-mediated effects (U69593 on the MPLM. Ke naloxone = 9.0nM).

Table 2: Against potencies and antagonism by naloxone in the mouse vas deferens (MVD) and guinea-pig myenteric plexus-longitudinal muscle (MPLM) preparations.

MPLM MVD

Compound K ₅₀ /nM Ke(Nx)/ _n M K ₅₀ /nM Ke(Nx)/ _n M

moφhine 130.0 ± 7.2 3.45 ± 0.59 173.4 ± 62.8 3.60 ± 0.80

M-6-G 58.0 ± 4.3 3.00 ± 0.80 104.2 ± 17.1 2.61 ± 0.90

DAMGO 11.8 ± 1.2 1.60 ± 0.06 24.7 ± 3.0 1.90 ± 0.60

DPDPE NT NT 2.80 ± 0.63 20.4 ± 2.6

U69593 2.20 ± 0.41 9.00 ± 2.11 NT NT

NT = not tested

Morphine-6-glucuronide analogues

Opioid Binding Site Affinities

Analogues were tested and selected to at least retain and preferably exaggerate the relative binding profiles of M6G compared to moφhine, i.e. equivalent, high affinity at μ- sites. and decreased affinity at κ-sites. Initially, 6-substituted codeine derivatives (i.e. with a 3-OMe function) were investigated as target compounds. Such derivatives, e.g. 3-OMe, 6-phthalate (BTG 2379) were shown to have low affinity for μ-binding sites (Ki=4500nM, Table 3). 3-silylmoφhine (BTG 2381), however, itself retained a high affinity for μ-sites (Ki=2.5nM) and 3-silyl compounds were used as preparative intermediates for 6-substituted

analogues. The addition of an aromatic ring at the 6-position, particularly phthalate (BTG 2382) and to a lesser extent benzoate (BTG 2383), further beneficially modified the binding profile. Table 3 below shows that BTG 2382 and BTG 2383 retained affinity at μ-binding sites (Ki = 17.5 and 310nM respectively), whilst losing κ-binding activity (Ki = > 10,000nM) and retaining δ-activity, in the case of BTG 2382 the affinity at the δ- site being in fact enhanced markedly (Ki = 4. InM, Table 3). Analogues with 6-phthalate and 6-benzoate substitutions were investigated, therefore, returning to desilylated, moφhine based structures (i.e. 3-OH). As with the protected series and shown in Table 4, the 6-phthalate ester of moφhine (BTG 2403) retained good affinity at the μ-binding site (Ki = 27.8nM), slightly higher affinity at the δ-binding site (14.2nM) and low affinity at the κ-binding site (Ki = 2774nM). A series of para substituted 6-benzoate analogues (Table 4) demonstrated that the 6-(p-nitrobenzoate) ester (BTG 2404) showed a related profile with again good affinity at the μ-binding site (Ki = 30. InM), slightly lower affinity at the δ-binding site (Ki = 68.5nM), but no demonstrable affinity at the κ-binding site, at least up to 10,000nM. The 6-(p-hydroxybenzoate) ester (BTG 2408) also displayed a related profile with high affinity at the μ-site (Kiμ = 1.7nM, Kiδ = 22.2nM, Kiic = 157nM; Table 4). Moφhine-6-phthalate (BTG 2403), moφhine-6-(p-nitrobenzoate) (BTG 2404) and moφhine-6-(p-hydroxybenzoate) (BTG 2408), therefore, all extend the differences in binding profile seen in M6G compared to moφhine; all 5 compounds having μ-affinity in the l-30nM range, with δ-affinities, ranging from moφhine of 218nM to BTG 2403 of 14.2nM, and -affmity, ranging from moφhine of 84.7nM to BTG 2404 of >10,000nM.

Table 3: Affinity of 3,6-substituted morphine derivatives at mu, delta and kappa binding sites in mouse brain homogenates.

Ki (nM)

Compound Ri *2 μ δ K BTG moφhine H H 6.22 ± 0.86 218.0 ±41 84.7 ± 4.0 codeine M _e H 2700± 3.02 NT NT

2379 M _e phthalate 4500±513 NT NT

2381 silyl H 2.50 ±0.41 175 ±6 135 ±14

2382 silyl phthalate 17.5 ±2.8 4.1 ±0.3 > 10,000

2383 silyl benzoate 310±22 485 ± 25 > 10,000

Table 4: Affinity of 6-substituted morphine derivatives at mu, delta and kappa binding sites in mouse brain homogenates.

Ki (nM)

Compound *3 R ₄ μ δ K BTG moφhine 6.22 ± 0.86 218.0 ± 41.2 84.7 ± 4.0

M-6-G 7.90 ± 1.48 75.1 ± 15.6 850 ± 118

2403 COOH H 27.8 ± 3.8 14.2 ± 2.9 2774 ± 205

2404 H NO ₂ 30.1 ± 1.4 68 ± 4.6 > 10,000

2405 H F 16.6 ± 3.2 83.3 ± 6.8 193.2 ±14.1

2406 H Cl 17.7± 2.8 84.9 ± 8.4 149.9 ±12.2

2407 H Br 28.4± 5.2 205.0 ±10.2 832.9 ±24.1

2408 H OH 1.73± 0.26 22.2 ± 3.4 157.0 ±12.6

Opioid activity on isolated tissues

The above series of 6-substituted moφhine derivatives was tested for activity on the isolated tissue preparations described previously. The results are shown in Table 5.

Table 5: Potencies of 6-substituted morphine derivatives in the guinea-pig MPLM and mouse vas deferens (MVD) preparations.

ιc ₅₀ nM

Compound 6- MPLM MVD BTG substitution moφhine H 130.0 ± 7.2 173.4 ± 62.8

M-6-G glucuronide 58.0 ± 4.3 104.2 ± 17.1

2403 phthalate 350 ± 25 24.3 ± 3.5

2404 p-NO ₂ -bz 132 ± 12 1166 ± 467

2405 p-F-bz 1010 ± 102 1325 ± 262

2406 p-Cl-bz 1506 ± 161 1162 ± 151

2407 p-Br-bz 1800 ± 183 1281 ± 186

2408 p-OH-bz 9004 ± 106 230 ± 18

As discussed previously, although M6G has a slightly higher affinity in brain homogenate preparations for δ-binding sites compared to moφhine (approximately 3-fold increase), on a relevant isolated tissue preparation, the mouse vas deferens (MVD), the potency difference is small (approximately 1.7-fold). Studies with the opioid antagonist naloxone on the MVD show that M6G, like moφhine, is still acting yja. μ- and not δ- receptors in this tissue. It was of interest, therefore, to investigate whether representative examples of the

6-substituted analogues with high δ-binding affinity in mouse brain homogenates were exerting their agonist effects on the MVD through μ- or δ-receptors in this isolated tissue.

3 compounds were studied, 3-silylmoφhine-6-phthalate (BTG 2382, Ki δ binding = 4. InM), moφhine-6-(p-nitrobenzoate) (BTG 2404, Ki δ binding = 68.5nM) and moφhine-6-(p-hydroxybenzoate (BTG 2408, Ki δ binding 22.2nM). The respective

IC50S of these compounds on the MVD were 41nM, 1166nM and 230nM. As shown in

Table 6, the Ke's for antagonism by naloxone of BTG 2382, BTG 2404 and BTG 2408 were similar and in the range 14.9 - 20.2 nM. The concentrations of naloxone required for

antagonism of the analogues are considerably higher (approximately 6-7 times) and in marked contrast to that required for equivalent antagonism by naloxone of moφhine and M6G (Ke naloxone = 3.6nM and 2.6nM respectively).

Thus, whereas in the MVD isolated tissue preparation moφhine and M6G act via μ-receptors, the 6-substituted moφhine analogues tested acted on this tissue v__ δ- receptors.

As may be expected, on the guinea-pig ileum myenteric plexus-longitudinal muscle (MPLM) preparation which lacks functional δ-receptors, naloxone antagonism of all 5 compounds showed similar Ke's (range 3.0 - 4.1 nM) indicating their action on this tissue is via μ-receptors.

Table 6: Antagonism by naloxone of morphine and derivatives on the MPLM and MVD isolated tissue preparations.

Compound Substitution Ke naloxone nM

BTG 3- 6- MPLM MVD

moφhine OH H 3.5 ± 0.6 μ 3.6 ± 0.8 μ

M-6-G OH glucuronide 3.0 ± 0.8 μ 2.6 ± 0.9 μ

2382 silyl phthalate 4.1 ± 1.4 μ20.2 ± 3.0 δ

2404 OH p-NO -bz 3.5 ± 0.3 μl4.9 ± 1.5 δ

2408 OH p-OH-bz 3.2 ± 0.4 μl7.8 ± 1.9 δ

IN VIVO EXPERIMENTS :

EXAMPLE 4: GENERAL METHOD FOR ASSESSING THE ANTTN CICEPTTVF

ACTIVITY OF COMPOUNDS OF THE INVENTION

The antinociceptive effects of moφhine and moφhine-6-glucuronide in animals (and analgesia in man) are well known. In the present studies, therefore, only one confirmatory study was carried out in the mouse tail-flick test which showed, by subcutaneous administration, moφhine and moφhine-6-glucuronide to be equipotent,

ED50 = 2.2 gl/kg and 1.9 mg/kg respectively, see Table 5 below.

Male CSI mice (25.30 g) (University of Nottingham Medical School) were used in these experiments. Animals were housed in groups of twelve in a room with a temperature controlled at 20°C on a 12 hour light-dark cycle and with free access to food and water.

Compounds of the current invention moφhine sulphate and related compounds or vehicle controls (saline with 0.25% carboxy- methylcellulose) were injected subcutaneously. Six control mice (injected with vehicle) and six test mice were used for each study. Where antagonists were used these were injected subcutaneously 15 minutes prior to the agonists. Antinociceptive activity was determined by the mouse tail-immersion test as follows:

Prior to injection and at the stated times past injection the tail was immersed in warm water at 50°C. The time for withdrawal of the tail was recorded. Antinociception was determined by an increase in the time-latency to withdrawal. The cut-off time for non-responding animals was 10 seconds. The time to reach maximal analgesie was deduced and ED50 values obtained for each drug as a measure of potency. The same points were subtracted from the test points and the dose required to give 50% of the maximal tail-flick latency (ED50) was deduced. The results are shown in the following Tables.

Table 7: Antinociceptive activity of morphine-6-p-nitrobenzoate and morphine-6- phthalate in the mouse warm-water tail flick test

Compound Tail-flick latency(s)

Morphine-6-p-nitrobenzoate vehicle control drug

1 mg/kg 2.2 ± 0.4 2.6 ± 0.4

3 mg/kg 1.9 ± 0.2 2.7 ± 0.1

10 mg/kg 1.3 ± 0.2 2.1 ± 0.1

30 mg/kg 1.7 ± 0.1 5.0 ± 0.1*

Morphine-6-phthalate

1 mg/kg 1.3 ± 0.1 2.3 ± 0.3

3 mg/kg 2.7 ± 0.2 5.5 ± 0.3*

10 mg/kg 1.7 ± 0.2 6.7 ± 0.3*

30 mg/kg 1.4 ± 0.2 8.2 ± 0.9*

Drugs were administered s.c. in saline containing 0.25% carboxylmethylcellulose and tail-flick latencies were measured at 50°C, 60 minutes later. There were six animals in each group *P<0.05 (Wilcoxon signed rank test).

Table 8: Time course of the antinociceptive activity of morphine-6-j}-nitrobenzoate (10 mg kg s.c.) and morphine-6-phthalate (10 mg/kg s.c.) in the mouse warm-water tail-flick test

Tail-flick latency (s)

Time (mins) vehicle control morphine-6- -nitrobenzoate morphine-6-phthalate

-15 2.5 ± 0.2 1.9 ± 0.2 2.3 ± 0.2

15 2.8 ± 0.3 2.8 ± 0.5 3.0 ± 0.4

30 3.2 ± 0.4 5.3 ± 0.5* 4.6 ± 0.3*

60 2.9 ± 0.3 7.3 ± 1.0* 5.9 ± 0.5*

90 3.0 ± 0.3 8.9 ± 0.9* 6.2 ± 0.6*

120 2.8 ± 0.2 8.4 ± 0.8* 7.0 ± 0.5*

240 2.6 ± 0.2 4.1 ± 0.9* 3.4 ± 0.3*

360 2.3 ± 0.2 2.2 ± 0.3 2.1 ± 0.2

Drugs were administered s.c. in saline containing 0.25% carboxymethylcellulose and tail-flick latencies determined at 50°C at the stated times. There were 6 mice in each group. *P<0.05 (Wilcoxon signed rank test).

Discussion

Tables 7 and 8 show dose-related antinociceptive activities of the moφhine-6- phthalate (BTG 2403) and moφhine-6-D-nitrobenzoate (BTG 2404) on subcutaneous administration in the mouse tail-flick assay. BTG 2403 was slightly more potent than BTG 2404, IC50S being 2.6 mg/kg and 16.2 mg/kg respectively.

Data from similar experiments with moφhine (5 mg/kg and moφhine-6- glucuronide were compared. The results are shown in Tables 9 and 10 below.

Table 9: Time Course Experiment of the antinociceptive activity of morphine, 5mg/kg s.c. and morphine-6-glucuronide (M6G) 5mg/kg s.c. in the mouse warm water flick tail test

Time (mins) Vehicle Morphine- Vehicle M6G

Control treated Control treated

-15 2.2 ± 0.3 2.1 ±0.2 2.6 ± 0.3 1.8 ±0.3

15 2.6 ± 0.4 8.5 ± 0.6 * 3.6 ±0.5 7.6 ±1.2*

30 3.8 ±0.3 9.8 ±0.2* 2.9 ± 0.4 10*

60 2.9 ± 0.2 10* 3.4 ±0.3 10*

90 2.7 ± 0.2 9.8 ±0.2* 2.8 ± 0.3 10*

120 3.0 ±0.2 7.9 ±0.5* 3.0 ±0.2 10*

240 2.7 ± 0.2 4.9 ±0.6* 3.0 ±0.2 10*

360 2.8 ± 0.2 2.7 ±0.2 2.5 ± 0.2 10*

540 NT NT 2.5 ± 0.2 7.1 ±0.9*

720 NT NT 1.8 ±0.2 3.2 ±0.5*

1440 NT NT 1.8 ±0.1 2.0 ± 0.4

NT = not tested

Drug was administered s.c. (sub-cutaneously) in saline and tail flick latencies (50° water) determined at the stated times. A cut-off time of 10 seconds was used. There were six mice in each group * P < 0.05 (Wilcoxon signed rank test).

Table 10 : Dose effect responses for the antinociceptive effect of morphine and morphine-6-glucuronide (M6G) in the mouse warm water tail-flick test

Tail flick latency (seconds)

Compound Morphine M6G mg/kg

0 2.4 ± 0.3 2.3 ± 0.1 0.3 3.5 ± 0.4 * 3.4 ± 0.3 * 1.0 3.9 ± 0.4 * 3.8 ± 0.5 * 3.0 7.0 ± 1.0 * 9.2 ± 0.6 * 5.0 10 * 10 * 10.0 10 * 10 *

Drug was administered in saline, subcutaneously, using 6 mice for each concentration. Tail flick latencies were determined 60 minutes after injection using 50 ^β C water. A cut-off time of 10 seconds was used. * Represents P < 0.05 (Wilcoxon signed rank test)

Peak antinociceptive activity with BTG 2403 and BTG 2404 (120 minutes and

90 minutes) was delayed compared to that of moφhine (60 minutes) and activity by all 3 compounds had returned to control levels 360 minutes after subcutaneous administration.

With an extension of the profile of the 6-substituted analogues in binding and in vitro studies demonstrating increased affinity and actions mediated by the δ-receptor, one compound, the 6-phthalate ester of moφhine (BTG 2403), was tested for δ-mediated effects in an antinociceptive test, the mouse tail-flick. Results are shown in Table 11. Moφhine (5mg/kg) and BTG 2403 (30mg/kg), administered subcutaneously, demonstrated approximately equivalent antinociceptive effects. The selective δ-receptor antagonist naltrindole (1 mg/kg sc) completely antagonised the effects of BTG 2403, but had no effect on those induced by moφhine. BTG 2403 would appear to exert antinociceptive effects via δ-opioid receptors.

Table 11: Effect of naltrindole (1 mg/kg) on the antinociceptive activity of morphine (5 mg/kg) and morphine-6-phthalate (30 mg/kg) in the mouse warm-water tail-flick test

Treatment Tail-flick latency(s) pre-test 2.0 ± 0.3 vehicle 2.3 ± 0.2 naltrindole 2.2 ± 0.2 moφhine 10.0 (cut-off)* moφhine + naltrindole 10.0 (cut-off)* moφhine-6-phthalate 9.8 ± 0.2* moφhine-6-phthalate + naltrindole 2.5 ± 0.3

Drugs were administered subcutaneously in saline containing 0.25% carboxymethylcellulose and tail-flick latencies were determined at 50°C 90 minutes (moφhine) or 120 minutes (moφhine-6-phthalate) later. Naltrindole was administered 15 minutes prior to the agonists. *P<0.05 (Wilcoxon signed rank test).

EXAMPLE 5: ANTINOCICEPTIVE EFFECTS OF MORPHINE AND DERIVATIVES ORAL ANALGESIC STUDY:- PAW LICKING TEST IN MICE Male, LACA mice (Tucks), weighing between 30-40g, were dosed orally with the vehicle or compound, 1 h prior to the sub-plantar injection of 10 μl of 5% formalin. The duration of paw licking was measured 0-5 min and 15-30 min after formalin administration. The vehicle was 0.25% carboxymethylcellulose in 0.9% saline and solutions were sonicated and shaken prior to administration; this was especially necessary for the high concentrations of the two test compounds (moφhine-6-phthalate and moφhine-6-p.- nitrobenzoate).

All experiments were performed between 1400-1700h and in any one experiment at least one control animal and three of the compounds were studied.

Animals were removed from the animal house at 1300h and the temperature of the behavioural room was noted (it did not exceed 25 °C although several of the experiments were performed when the outside temperature was 30-35 ^β C).

The duration of licking in the treated groups was compared with that of the controls using one-way ANOVA followed by the Dunnett Multiple Comparison Test. A non- parametric test (Kruskal-Wallis, followed by Dunn's Multiple Comparison Test) was also used as there was some concern about the normal distribution of the values. Calculations were performed through the INSTAT programme. The results are shown in Table 12 below

Table 12: Antinociceptive effects of morphine and derivatives

Antinociceptive effect

Compound 6- tail-flick paw-lick BTG substitution ED 50 mg/kg lowest dose * sc po moφhine OH 2.2 ± 0.3 10.0

M6G glucuronide 1.9 ± 0.3 No effect at 80

2403 phthalate 2.6 ± 0.4 40.0

2404 p-NO ₂ -bz 16.2± 2.6 40.0

* lowest dose producing a statistically significant (p < 0.05) antinociceptive effect.

Moφhine induced, dose related antinociceptive effects were observed at doses of 10 mg/kg and higher. In comparison, moφhine-6-glucuronide failed to induce statistically significant antinociceptive effects at any dose tested (10-80 mg/kg po). BTG 2403 and BTG 2404 (both at 40 mg/kg) induced antinociceptive effects on oral administration although dose related effects with a highest dose were demonstrated only with the latter compound.

Both the 6-substituted aromatic analogues, therefore showed statistically significant oral antinociceptive effects, the compound being slightly less potent than moφhine, but more potent than moφhine-6-glucuronide, which failed to demonstrate antinociceptive effects, even at the highest dose tested.